CYBERCOMP.CO.CC

Linksys Media Hub NMH305

2009-02-09T02:09:00.000-08:00

Storage is a crucial part of the digital lifestyle: We all need a place to put our stuff, and we need a way to access those files easily. Linksys has tried a few storage products in the past, but the Media Hub is its most ambitious effort. While it's not exactly a small business server that lets you set up user accounts – like the HP MediaSmart EX487 – and can't compete with the robust RAID and back-up options on Netgear ReadyNAS devices or those by Buffalo Technology, it has one glowing attribute: it's easy to use. Like most Apple products including the still viable Time Capsule, the Media Hub assumes you are not a certified Microsoft engineer or someone who carries USB key drives in your pocket 24x7. It's a smart product that eases you into the deeper features, with only a few caveats.

Setting up the Media Hub takes all of about three minutes. Connect one Ethernet cord to your router, turn it on, and you're done. Because the drive supports UPnP and works well with Windows, Apple iTunes, the Mac (thanks to Bonjour), and even Linux, you can expect to see the drive on your network without installing a driver or fussing with an IP address. Only when you do want to dive into the advanced features will you need the included setup CD or to access the drive's IP.

This NAS matches the styling of the new Linksys Multi-Room Home Audio gear – which is to say, it's gray and black and nothing too special compared to more elegantly designed network-attached storage devices. The difference between a media player you'd stick next to an HDTV, and this product, is that it will likely sit in a back closet somewhere. The Media Hub has two USB ports, one on the front and one on the back. There are very few buttons and lights. The NMH305 base model ships with one 500GB SATA drive and has one open bay. There's a power light and drive activity light – Linksys plans to release two additional models with higher capacities and an LCD screen that reports on drive status.

Performance on the Linksys Media Hub is just ho-hum – it's not going to set any speed records. About 6GB of MPEG-4 movie files took six minutes to transfer to the Media Hub, whereas the same transfer took 3 minutes to send to a home-built Windows Home Server and only 1 min 40 seconds to copy to the HP MediaSmart EX487 server. A 700MB collection of photos and documents took 50 seconds to write to the drive and 50 seconds to read, about 15 seconds longer than it took on the HP MediaSmart. The drive really showed some pokey behavior when we performed a full back-up of a desktop, which took about ten hours for about 200GB of data. The Media Hub has a gigabit Ethernet port, so it should be no slouch, but a real server adds some extra features to speed up disk copies.

source : reviews.digitaltrends.com

Networking Topology

2009-01-29T08:54:00.000-08:00

Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.

Network topologies are categorized into the following basic types:

bus
ring
star
tree
mesh

More complex networks can be built as hybrids of two or more of the above basic topologies.

Bus Topology

Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI,SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

Star Topology

Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch, and router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Tree Topology

Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Mesh Topology

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

Summary

Topologies remain an important part of network design theory. You can probably build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies gives you a better understanding of important networking concepts like hubs, broadcasts, and routes.

source : compnetworking.about.com

Simple Steps To Basic Wireless Hacking

2009-01-28T12:25:00.000-08:00

The intent of this article is to show you information on basic wireless hacking along with just how important it is to secure your wireless Network. Please use this information wisely. I am not responsible for what you and your friends do with this information.

Today it is very easy to set up a wireless network. Basically plug in the router a few clicks on your computer and away you go. The average person can go to his or her local electronic store and pick up a wireless router for as cheap as 40 bucks. The Problem comes in when securing the network. A large amount of people don't take the time to learn how to, or care to set up security.. How much damage can some one do if they connect to a wireless network?

Well in this article I will show you just how easy it is to connect to one of these unsecured networks and what kind trouble can be caused. I am going to use just some built in tools of Windows.

How Simple is it to find a Unsecured Network?

In this example I am just using the windows wireless management tool. This will work fine if you are not on the move. If you are scanning for networks in a car or on your bike I would strongly recommend NetStumbler .

As you can see here just by looking at what networks are available close to my home, There is at least one unsecured network. I would be willing to bet you could go around your block and find at least one open network. I am going to use this Linksys network in my example.

So just how simple is it to connect to an Unsecurred network?
I just double clicked on the open linksys network.
It will warn you that you are connecting to a unsecure network.

Click Connect Anyways

Now I can start Browsing the Internet

What can some one do if they connect to unsecured network?

In this example this wireless network is still set at the default settings including the Administrator password. A simple search on http://www.routerpasswords.com you can find just about any wireless router Default password. SInce this is a linksys router the default password would be admin. Since most wireless routers are the default gateway, I will do a quick command in dos to find out what the default gateway is.

Click on start > Run

Type CMD and click ok

In the Dos window type ipconfig then hit enter

I look for the information under my wireless network card. The default gateway is 192.168.1.1 Type this in your Browser to connect to the router.

You will be prompted for a username and password.

Leave the username blank or type root

Since this is a linksys router I will use the password admin

To find out the default password for just about any router check out

http://www.routerpasswords.com/

If they did not change there router password you should be able to get in to the configuration pages of the router.

I am now connected to the router. This gives me complete access to see who is on the network. I can also do things such as set up security, open ports, and so much more.

How do you see who is connected to the network?

- Click on Status

- Click on Local Network

- Click on DHCP Client Table button

You should now see all computers that have been assigned an IP address by the router. Not all the computers on the network may not be connected at that time but a simple ping will let you know.

You could run a port scanner on each of these computer's IP address to find open ports such as ssh, telnet, termainal service and so on.

SInce we are able to configure the router we could open up ports and let any one on the internet have access to this network. We could also have a little fun by setting up wireless security on the network and locking out the owner of his or her's own network.

Lets say you could not get in to configure the router there still is a lot of trouble that can be caused just by being connected on the network. You could set up a Network packet capturing program such as Ethereal. Then use it to Scan for information such as username and passwords from websites they may login to.

You could also go out and cause some trouble on the web and it would trace back to there IP address.

At the Least you could enjoy the free internet. You get lost some where, get connected real quick and take advantage of google maps. Could come in handy in a pinch.

I hope this article got you thinking a little bit and if your wireless network is not secure, I hope this has convinced you to take the time to set it up.

source : www.mixeduperic.com

Router Commands

2009-01-27T11:47:00.000-08:00

In this section you will learn about the router commands, configurations, privileged mode commands, routing protocols, cisco labs and network configurations.

There are hundreds of basic and advance level commands of a router. It is not easy to remember all the commands. But some commands are frequently used and can be remembered with some practice. I have provided a list of the most commonly used commands based on their features and usage. You will find here some basic terminology of a router.

Routing: Routing is a process of moving the data (packets) through an inter network. Routing performs the two basic tasks. Define the paths for a packet and then forward the packets on the basis of defined paths. Routing can also be defined as the communication between two or more logically and physical networks and this communication (packet transfer) is brought by a router.

First of all you should remember the keyboard shortcuts of a router.

Keyboard Shortcuts
CTRL-N - show next command
CTRL-P - show previous command
SHIFT-CTRL-6 – Break

Configuring the Router

You will be able to learn the basic commands for configuring a router.
sh running-config - details the running configuration file (RAM)
sh startup-config - displays the configuration stored in NVRAM
setup - Will start the the automatic setup; the same as when you first boot the router
config t - use to execute configuration commands from the terminal
config mem - executes configuration commands stored in NVRAM; copies startup-config to running-config

config net - used to retrieve configuration info from a TFTP server
copy running-config startup-config - copies saved config in running config (RAM) to NVRAM or "write memory" for IOS under ver.11
copy startup-config running-config - copies from non-volatile (NVRAM) to current running config (RAM)
boot system flash - tells router which IOS file in flash to boot from
boot system tftp - tells router which IOS file on the tftp server to boot from
boot system rom - tell router to boot from ROM at next boot
copy flash tftp - Copies flash to tftp server
copy tftp flash - Restores flash from tftp server
copy run tftp - Copies the current running-config to tftp server
copy tftp run - Restores the running-config from tftp server

General Commands

Here is a list of the general commands. These are the basic level commands and most commonly used
no shutdown - (enables the interface)
reload - restarts the router
sh ver - Cisco IOS version, uptime of router, how the router started, where system was loaded from, the interfaces the POST found, and the configuration register
sh clock - shows date and time on router
sh history - shows the history of your commands
sh debug - shows all debugging that is currently enabled
no debug all - turns off all debugging
sh users - shows users connected to router
sh protocols - shows which protocols are configured
banner motd # Your customized message here # - Set/change banner
hostname - use to configure the hostname of the router
clear counters - clear interface counters

Privileged Mode commands of a router

Learn how to work in the privileged mode of a router.
enable - get to privileged mode
disable - get to user mode
enable password - sets privileged mode password
enable secret - sets encrypted privileged mode password
Setting Passwords on router
Here you will be able to learn how to set the password on a router.
enable secret - set encrypted password for privileged access
enable password - set password for privileged access (used when there is no enable secret and when using older software)
Setting the password for console access:
(config)#line console 0
(config-line)#login
(config-line)#password
Set password for virtual terminal (telnet) access (password must be set to access router through telnet):
(config)#line vty 0 4
(config-line)#login
(config-line)#password
Set password for auxiliary (modem) access:
(config)#line aux 0
(config-line)#login
(config-line)#password

Router Processes & Statistics

By these command you can see the statistics and different processes of the router.
sh processes - shows active processes running on router
sh process cpu - shows cpu statistics
sh mem - shows memory statistics
sh flash - describes the flash memory and displays the size of files and the amount of free flash memory
sh buffers - displays statistics for router buffer pools; shows the size of the Small, Middle, Big, Very Big, Large and Huge Buffers
sh stacks - shows reason for last reboot, monitors the stack use of processes and interrupts routines

IP Commands

Here is a list of the IP Commands
Configure IP on an interface:
int serial 0
ip address 157.89.1.3 255.255.0.0
int eth 0
ip address 2008.1.1.4 255.255.255.0

Other IP Commands:

sh ip route - view ip routing table
ip route [administrative_distance] - configure a static IP route
ip route 0.0.0.0 0.0.0.0 - sets default gateway
ip classless - use with static routing to allow packets destined for unrecognized subnets to use the best possible route
sh arp - view arp cache; shows MAC address of connected routers
ip address 2.2.2.2 255.255.255.0 secondary - configure a 2nd ip address on an interface
sh ip protocol

CDP Commands (Cisco Discovery Protocol uses layer 2 multicast over a SNAP-capable link to send data):

sh cdp neighbor - shows directly connected neighbors
sh cdp int - shows which interfaces are running CDP
sh cdp int eth 0/0 - show CDP info for specific interface
sh cdp entry - shows CDP neighbor detail
cdp timer 120 - change how often CDP info is sent (default cdp timer is 60)
cp holdtime 240 - how long to wait before removing a CDP neighbor (default CDP holdtime is 180)
sh cdp run - shows if CDP turned on
no cdp run - turns off CDP for entire router (global config)
no cdp enable - turns off CDP on specific interface

IPX Commands

Enable IPX on router:
ipx routing
Configure IPX + IPX-RIP on an int:
int ser 0
ipx network 4A

Other Commands:

sh ipx route - shows IPX routing table
sh ipx int e0 - shows ipx address on int
sh ipx servers - shows SAP table
sh ipx traffic - view traffic statistics
debug ipx routing activity - debugs IPS RIP packets
debug ipx sap - debugs SAP packets

Routing Protocols

RIP, IGPR and OSPF are the routing protocols and here is a list of the commands for the working on the routing protocols.
Configure RIP:
router rip
network 157.89.0.0
network 208.1.1.0
Other RIP Commands:
debug ip rip - view RIP debugging info
Configure IGRP:
router IGRP 200
network 157.89.0.0
network 208.1.1.0
Other IGRP Commands:
debug ip igrp events - view IGRP debugging info
debug ip igrp transactions - view IGRP debugging info
Access Lists
Here is a list of the Access list command of a router.
sh ip int ser 0 - use to view which IP access lists are applies to which int
sh ipx int ser 0 - use to view which IPX access lists are applies to which int
sh appletalk int ser 0 - use to view which AppleTalk access lists are applies to which int
View access lists:
sh access-lists
sh ip access-lists
sh ipx access-lists
sh appletalk access-lists
Apply standard IP access list to int eth 0:
access-list 1 deny 200.1.1.0 0.0.0.255
access-list 1 permit any
int eth 0
ip access-group 1 in
Apply Extended IP access list to int eth 0:
access-list 100 deny tcp host 1.1.1.1 host 2.2.2.2 eq 23
access-list 100 deny tcp 3.3.3.0 0.0.0.255 any eq 80
int eth 0
ip access-group 100 out
Apply Standard IPX access list to int eth 0:
access-list 800 deny 7a 8000
access-list 800 permit -1
int eth 0
ipx access-group 800 out
Apply Standard IPX access list to int eth 0:
access-list 900 deny sap any 3378 -1
access-list 900 permit sap any all -1
int eth 0
ipx access-group 900 out

WAN Configurations Commands

Networking over WAN is the main functionality of a router. The most common use of a router is for the WAN connectivity. Here is a list of the commands for the different methods of the WAN connectivity.

PPP Configuration

Point to point protocol is a method for the WAN connectivity and you will find here some commands of PPP.
encapsulation pppppp authentication
ppp chap hostname
ppp pap sent-username
sh int ser 0 - use to view encapsulation on the interface

Frame-Relay Configuration

One of the methods for the WAN connectivity is the Frame Relay. Find here some basic commands for the WAN connectivity through Frame Relay.
encapsulation frame-relay ietf - use IETF when setting up a frame-relay network between a Ciscorouter and a non-Cisco router
frame-relay lmi-type ansi - LMI types are Cisco, ANSI, Q933A; Cisco is the default; LMI type is auto-sensed in IOS v11.2 and up
frame-relay map ip 3.3.3.3 100 broadcast - if inverse ARP won't work, map Other IP to Your DLCI # (local)
keep alive 10 - use to set keep alive
sh int ser 0 - use to show DLCI, LMI, and encapsulation info
sh frame-relay pvc - shows the configured DLCI's; shows PVC traffic stats
sh frame-relay map - shows route mapssh frame-relay lmi - shows LMI info

Miscellaneous Commands

In the last but not least here is a list of the some miscellaneous and useful commands
sh controller t1 - shows status of T1 lines
sh controller serial 1 - use to determine if DCE or DTE device
(config-if)#clock rate 6400 - set clock on DCE (bits per second)
(config-if)#bandwidth 64 - set bandwidth (kilobits)

source : www.networktutorials.info

Windows 7 Security

2009-01-26T07:14:00.000-08:00

By : Sonny Discini
Right now, Windows 7 looks very much like Windows Vista because enhancements to the appearance and feel aspects of the operating system typically come late in the development process. Lucky for us, much of the awaited security functionality has already made its way into the beta build and we're going to look at some of the new changes for Windows 7.

Old friends, new twists

Returning from Windows Vista are Kernel Patch Protection, Service Hardening, Data Execution Prevention, Address Space Layout Randomization, and Mandatory Integrity Levels

Windows XP SP2 gave us the Security Center. Windows 7 discards this and in its place is an Action Center that incorporates alerts from 10 existing Windows features: Security Center; Problem, Reports, and Solutions, Windows Defender; Windows Update; Diagnostics; Network Access Protection; Backup and Restore; Recovery; and User Account Control.

In Windows 7, users can adjust consent prompt behavior using a slider control, if they have administrative privileges. Microsoft says they'll still be protected against malicious software, even if they never see another alert. While this may or may not be true, users have been conditioned to see alerts whenever something is happening. Without them, perhaps a false sense of security will develop on the part of the end user.

Windows Filtering Platform

Windows 7 introduces something called the Windows Filtering Platform (WFP). The idea is that third parties can take advantage of aspects of the Microsoft Windows Firewall in their own products. Microsoft says "third-party products also can selectively turn parts of the Windows Firewall on or off, enabling you to choose which software firewall you want to use and have it coexist with Windows Firewall."

While this sounds nice on paper, I can't see a vendor teaming their product with the Windows firewall. Smart money says they'll just use their own and ignore the Microsoft solution.

One nice thing to note about Windows 7 is that it makes it easier to configure that all-important home network. When users hit network problems, they curse the firewall and they're often right to. Windows 7 addresses the problem by taking over home network setup and making sure the firewall doesn't interfere.

We also see that scrollbars were removed in the configuration settings screen, as has the Software Explorer feature, and real-time protection in Windows 7 has been improved to reduce the impact on overall system performance. A welcome change from the bloat of Vista.

An inclusive BitLocker

Vista sailed in along with a fleet of new security features, among them BitLocker, a whole-disk encryption tool designed to protect your data even after an attacker makes off with your laptop. BitLocker utilizes a chip called a Trusted Protection Module (TPM). The Vista TPM transparently decrypts the drive once you've authenticated yourself with a password or smart card. A laptop thief can't break into the locked drive, even after booting to a different OS or moving the drive to another computer.

BitLocker drive encryption also supports removable storage devices, such as flash memory drives and portable hard drives has been added in Windows 7. This means that users can keep sensitive data on all of their USB storage devices as well as the physical drives on the host mentioned above.

As a side note to Bitlocker, using groups, you can ban writing to any removable drive that isn't BitLocker-protected. It's a very useful tool against the very real problem known as podslurping. With this policy in place, employees can still bring in the virus-of-the-month on an unprotected drive, but they can't take away an unprotected copy of the personnel database. It's also helpful to know that BitLocker to Go also allows users to securely share data with other users who have not yet deployed Windows 7.

That said, the testing I performed proved otherwise. I could not get this to work so I went to Microsoft and they confirmed that this is an issue in the beta build but will be fixed before final GA release.

Biometrics, System Restore and AppLocker

Biometrics enhancements include easier reader configurations, allowing users to manage the fingerprint data stored on the computer and control how they log on to Windows 7. And System Restore includes a list of programs that will be removed or added, providing users with more useful information before they choose which restore point to use. Restore points are also available in backups, providing a larger list to choose from, over a longer period of time.

I've seen more problems caused by System Restore than solved by it; I'm not a big fan. Still, users often resort to it when trying to clean up a real or imagined malware problem. In Windows 7, you'll at least have a clear idea of what collateral damage may result, as it lists all programs and drivers that would be removed or brought back by invoking a particular System Restore point. It's way better than guessing at the right restore point and hoping for the best, which is what you have to do now.

Another enhancement is AppLocker, accessed through Local Security Policy. It's a way to control which programs users can and can't use, and it's a lot more flexible than Vista's Software Restriction Policies. Still, it's not for the average user. Most IT shops should be pleased with this enhancement. I can see it being tailored to just about any corporate need.

Virtually all the changes in the security area are simply tweaking and improving on existing Vista features. But then, that's what Windows 7 is all about, right? While the enhancements seen thus far in the beta are nice, they aren't stunning.

I hope to see even more improvements before Windows 7 hits the streets.

source : www.enterpriseitplanet.com

Save your computers from Spyware

2009-01-21T12:06:00.000-08:00

The best defense against spyware and other unwanted technologies is to prevent them from getting on your computer in the first place. Awareness is the best approach to protect yourself online, so staying up-to-date on current threats and safe surfing practices is essential. Here are some steps you can take to stay safe while still getting the most from the Internet and software programs.

Keep security on your computer up to date.

Update security patches:

Many malicious spyware developers exploit known security holes in essential software, such as operating systems and browsers. Update essential software frequently. Automate the process if your vendor offers the option.

Security and privacy settings in Internet browsers:

Many Internet browsers have security and privacy settings that you can adjust to determine how much—or how little—information you are willing to accept from a Web site. Check the documentation or help file on your Internet browser to determine how to adjust these settings to appropriate levels. See GetNetWise.org for detailed instructions.

Download programs only from Web sites you trust.

If you are not sure whether to trust a program you are considering downloading, ask a knowledgeable friend or enter the name of the program into your favorite search engine to see if anyone else has reported that it contains spyware or other potentially unwanted technologies.
Look carefully at the address of the site you are visiting to make sure it is not an obvious spoof.
Be particularly suspicious of programs you see advertised on unrelated Web sites. If a maker of a screensaver, “smiley” inserter, or other program heavily promotes its purportedly-free product, the product may include extra software you do not want.

Beware the fine print: Read all security warnings, license agreements, privacy statements, and “opt-in” notices with any software you download.

Whenever you install something on your computer, make sure you carefully read all disclosures, including the license agreement and privacy statement. Sometimes important information such as aggressive installs or the inclusion of unwanted software in a given software installation is documented, but it may be found only in the EULA. The fine print may be the only place consumers can find notice of potentially unwanted technologies. Unfortunately, careful consumers must read all the fine print.
When given the choice of opting into something, make sure you understand fully to what you are agreeing.
If you have doubts about the legitimacy of the software, do not install it, or go to a trusted source to find more information about the software. To be safe, you should never install software if you are uncertain about it.

Don’t be tricked into clicking: You don’t have to click “OK,” “Agree,” or “Cancel” to close a window.

If you want to close a window or dialog box, consider the options provided by your operating system or Web browser, such as closing the window with the ‘x’ mark in the upper corner or typing Alt+F4 in Microsoft Windows.
Pay attention when closing windows; some dialog boxes may have a prominent statement that says, “Click here to close window,” then in less prominent text adds, “and install software.”

Be especially careful with certain types of “free” programs.

Many file sharing applications are bundled with other, potentially unwanted software.
Similarly, screen savers, cursor enhancements, wallpaper bundles, “smiley” inserters and any other software promoted aggressively often include extra software you did not request and aren’t expecting. Be sure you clearly understand all of the software packaged with those programs.

Use available tools to detect and delete spyware.

There are a number of security tools available from a variety of vendors that can help you identify spyware, stop the installation of it on your PC, and/or remove it.
Anti-spyware and Anti-virus software:

There are a number of programs (available both free and for a fee) from reputable vendors that can help detect spyware, prevent spyware from being installed on your PC, and/or remove spyware if it is installed. (Some programs can be removed through “Add/Remove programs” or other standard operating system features.) Note that some software that claims to be an anti-spyware tool is actually adware or other potentially unwanted software in disguise. For this reason, you should read reviews to be sure any anti-spyware software you download is from a reputable publisher.

Personal firewall:

Installing and using a firewall provides a helpful defense against remote installation of spyware by hackers.

We encourage you to learn more about how to protect yourself from spyware by visiting the US federal government OnGuard OnLine Web site at http://www.onguardonline.gov.
source :www.antispywarecoalition.org

MAKE OMNI ANTENNA

2009-01-17T23:17:00.000-08:00

Introduction

Most of the designs on the web for 2.4 GHz omni antenna seem to involve brass tubing and lmr-400 cable, none of which are readily available to me. I then found a coax only design for 444Mhz that was based on the same idea. The only reasonable cable I could get my hands on was RG-213 from Maplin. By scaling the 444Mhz design up to 2.4 Ghz and using RG-213 I thought I'd have a go. In order to get about 6db gain from the antenna, it would need 8 sectors, with a 1/4 wave section at the top and a fly-lead with N-connector at the bottom. It should take about 2-3 hours to build an antenna using this design, but don't worry if it takes longer, you will get quicker, especially as you only need to make the jig once.

Most of the designs either had toroid magnets or a decoupler on the fly-lead of the antenna. However the location of the decoupler seems different in each design, and some designs quoted a decoupler length of 1/4 wavelength, others were !/4 wavelength times the velocity factor of the decoupler tube (brass tube quoted at 0.95). I've tried most locations and can report that without proper testing kit I can see no difference in the Signal to Noise ratio between having a decoupler and not. I decided to not bother as it simplified the design. If anyone knows a good reason why you must have a decoupler then I would love to know (especially if you know where it should be exactly). If you want to add a decoupler, please do, I found using 15mm or 22mm copper tube and a 15mm or 22mm end stop made a good design, just needing to be soldered together to get the right length, and a hole drilled in the end of the end stop to fit the cable.

Each sector of the antenna needs to be a 1/2 wavelength long multiplied by the velocity factor of the cable. The velocity factor of RG-213 is 0.66 . If you decide to use different cable (such as LMR-400) then you need to get the velocity factor of that cable (which will be different), and recalculate all the dimensions.

V * C 0.66 * 299792458
1/2 wavelength = ------ = ---------------- = 0.0405m = 40.5mm
2 * F 2 * 2441000000

V = Velocity Factor of RG213 = 0.66
C = speed of light = 299792458
F = Frequency of Signal = 2441000000 (middle of 2.4ghz range)

The 1/4 wave element is not adjusted by the Velocity factor, as it is in the open, so works out at just 31mm long giving a total antenna length of 355mm + fly-lead. (Thanks to Oscar for correcting me of this.)
Getting the parts

All of the parts are available cheaply from either Maplin and any diy shop.

* 1m RG-213U cable (available by the meter from Maplin). This is enough for 2 antenna. Buy more for whatever flylead length you want.
* N connectors, Depending on what you want to connect to , use either male or female connectors, and inline or bulkhead. Remember inline connectors need to fit 10mm diameter RG-213 cable
* 20mm pvc conduit (available from any diy store) Has a 20mm inside diameter, and 22mm outside.
* 22mm pipe clips (depending on how you want to mount the antenna), pipe clips make it easy to mount and unmount, or use the proper conduit brackets (but they seem a little expensive).

You don't need any special tools

* mm rule for measuring !
* junior hacksaw
* stanley knife
* pliers
* standard soldering iron (don't need a heavy duty one) and solder
* off cuts of wood to make a jig to aid soldering
* bench or vice to hold cable while you cut it

Cut the pieces

After much trial and error, I found that the neatest way to cut the cable is actually with a junior hacksaw. It gives a much cleaner finish than wirecutters. Each sector consists of a short length of RG-213 cable, with the central core sticking out each end.

When building the antenna, the exact length of each piece of RG-213 is not that important, it is the overall length of each sector that counts. I found that cutting the cable to 37mm with 6mm of core sticking out each end, gets enough overlap to easily solder the segments together. If you allow 1mm for the width of the hacksaw when cutting the sectors apart, it means you need 37 +6 +6 +1 = 50mm of cable for each sector making 8sectors + 1/4wave section come to 420 mm of cable for the antenna + cable for the fly lead.

The best way to cut each sector is to make the cuts where each end of the sheathed section of the sector will be, before making the cut between each sector. The picture below shows the top 3 sections of the antenna, and the 1/4 wave section, showing the order that the cuts should be made.

The best way to make the cuts is to mark them out on the cable first. When sawing the cable it has a tendancy to deform and bend, so lightly sawing round the outside sheath first, but not cutting through, helps give a guide to the cutting for real. I use the junior hacksaw to gently saw round the cable sheath to make the mark for each section.

The first mark will be at 31mm from the end, which is for the 1/4 wave section at the top. Once you have made the mark, it is time to cut round the cable. You want to cut through the sheath, shielding, and just into the central insulation, but not into the central copper wires. You may need to practice a bit first, but you should be able to feel as you cut through the shielding into the central insulation. By leaving plenty of sheathed section either side of the cuts, the shielding stays in place when being cut.

Now with pliers, gently twist off the end 31mm of sheath & shielding

This should leave the cenral insulator exposed. Using the stanley knife score round through the central insulator, but not too hard, or you will cut the central cable. Now twist off the insulation. You should be able to see the twist in the central cable through the insulation, which will show you which way to twist off the insulation, resulting in the central core twisting more tightly.

The next mark is 37mm down (68mm from end of the cable) and is the cut for other end of the sheathed section of the top sector. The next mark is 13mm down (consists of 6mm core from each sector and 1mm for cut between sectors) (81mm from end) and is the top of the sheathed section of the second sector. The next mark is 37mm down, then 13mm, then 37mm, and so on and so forth until you have each of the sheathed sections marked out.

You can now start making the cuts, remembering to only cut through the sheath, shielding and just into the central insulation. First make the cut at 37mm down, then the next cut a further 13mm down. You may find that some of the shielding pulls out when you make this cut, as the 13mm length of sheath cannot hold the shielding tight enough. Don't worry, it doesn't matter.

Now you are ready to cut off the top sector from the cable. You want to cut through the whole cable at the mid point of the two cuts you have just made, that is about 43.5 mm from the end of the sheath, or 74.5 mm from the end of the cable. See position 4 in the diagram above. Just saw carefully the whole way through the cable.

Now you can pull off the sheath and shielding from the each end.

Now score round the insulation as you did before, being careful not to cut the central cable

Now carry on making cuts 37mm down from the end of the sheath, and then 13mm further down (50mm from the end of the sheath), and then cut through the cable in the middle of the two cuts. Another sector made. You will need eight sectors in total. Make the same cuts as usual for the eighth sector as it will make top of the flylead as well. Now you have all eight sectors you need to check round the end of each sector to make sure that none of the shielding is touching the central cable, as odd strands can get left.

Now you need to make a gentle V shaped cut with the stanley knife, at each end of the sectors, to expose the shielding, which is where the central core of the next sector will be soldered.

Make sure that the V cuts at each end of the sector line up, othwise, when you come to solder the antenna together, the whole thing will be twisted all around. Once you have all eight sectors finished, its time to put them together.
Build a Jig
If you do not have a handy helper to hold the sectors together, then you will find it easier to make a small jig from offcuts of wood, to hold the sectors together as you solder them. The clamps on the right hand side of the picture need to be no more than 30mm long. The base board of the jig, needs to extend out to the right long enough to take the whole length of the completed antenna, as it will need to support it during the soldering, as the antenna is not rigid enough to support itself.

Don't make the clamps too tight, as you need to be able to easily lift the cable out after it has been soldered.

When you are readly to solder the sectors together, you need to take care , that each sector is correctly spaced. The overall length of each sector needs to be 40.5mm , measure from one end of the shielding of the sector you are adding, to the same end on the next sector, and slide the sectors together/apart until the distance is 40.5 mm. Try to get it as accurate as you can, as it affects the direction the antenna transmits in if you get it wrong. There should be a small 3mm gap between the sheaths of each sector.

Once you have soldered each sector together, lift it up, turn it over, and move it down the clamp ready for the next sector. This results in a nice straight antenna. When soldering, remember to heat both the shielding and core so that the solder runs smoothly and fixes them together.

Once complete, test the cable with either a bulb and battery or a multimeter. The center of the fly lead should form a circuit to the 1/4 wave section, and the shield of the flylead to the shield of the top section. Now test that there are no crossed connections, by ensuring there is no circuit between the center of the flylead and the shielding of the top sector, and no circuit between the 1/4 wave section and the shielding of the flylead.

Now fix the N connector of your choice onto the end of the fly lead. The type of connector you use depends on what you want to connect to. I use inline connectors, but you could use any connector you like. Slide the antenna into a length of conduiting. It should be a snug fit, you may need to gently ease it in. Now find an old soft drink bottle top, and pop it on the top end of the antenna. Voila one complete antenna ! Securing the antenna in the conduit is best left until you are ready to mount it somewhere. You can cut 5cm slots in the bottom if the conduit, and use a jubilee clamp to grip the flylead, or drill a hole through the conduit and use a cable tie to hold the fly lead, or use a bulkhead mount connector on a botle cap, and glue it to the bottom of the conduit, or glue the flylead in place. It's up to you.
Testing

I will assume you are connecting the antenna to a wireless card in a laptop, and connecting to an accesspoint somewhere. You will need to a signal to noise meter to examine the signal strength. Most wifi cards come with software that does this. Now its time to test that the antenna actually works. This can be harder than it sounds, as unless you can remove the existing aerial from the card or ap, you can't tell it is using your new homebrew antenna. Well wrapping the existing antenna completely in 6-8 layers of tinfoil, has a dramatic reduction on signal strength, now connect the antenna, and the signal should go back up. Remember that omni antenna send out the signal horizontally, so don't test it from the room below your access point. Hopefully you should see that your new antenna actually works. There are three ways to test the gain of the new antenna

* Use spectrum analyser in a professional radio lab
* compare the gain of your new antenna, to the gain of a known antenna (Not the pcmcia card)
* Carry out an empirical range test with your new antenna

If you have access to a spectrum analyser I'd love to know your findings. If you have an existing omni or yagi antenna, then you can compare the snr readings between the two antenna. Remember to do the test outside, as bouncing the signal off walls can really give odd results. Try to stand as far away from the antenna as possible when doing the test, as even moving near it can change the results a lot. Position the two antenna in the same place for the test. Don't try and compare the snr of your new antenna to that of the wireless card in your laptop, as just by turning the laptop round, or lifting it up, or holding it, can dramatically change the snr. Try it and see what I mean. If you don't have another antenna, then wander down your street until you are out of range. Now wander back towards your AP, and wait for the laptop to chime that it has made a connection. Note how far from home you are. Try it again, with the laptop connected to the new antenna. Remember to keep the antenna vertical. I found carrying them in a bag with the antenna poking out the top works well. Try not to hold the antenna, as this will change the snr. You should now be able to pick up your AP about twice as far away, assuming there are no new massive obstacles.

If you have a go at making this antenna, and get it working, drop me an email (address at bottom of page) and let me know how you found building it, whether you've found a simpler way, and ... be honest ... how long it took.

source : wireless.gumph.org

Top review of HSDPA Modem

2009-01-15T15:55:00.000-08:00

Here discuss about review HSDPA modem that may be tested that technology. This review I got from the people who already used. From here we can see what the feature, or the bad of HSDPA modem. I hope this review can be helping you to use HSDPA modem.

The Sierra Wireless AirCard 881U

At first glimpse, the AirCard 881U from Sierra Wireless is a beast of a gadget. Big, ugly, and surprisingly heavy, the USB modem isn't nearly as stylish as the other modems.
Similarly annoying is the install process. If you're a Windows user, it's easy -- simply pop the disc into your machine and follow the screen prompts. But if you're a Mac user, it's much more difficult. To install it on my Mac OS X 10.4 MacBook, I had to go to the Sierra Wireless Web page's support section and download the correct software for my operating system. Once that download was complete, I was finally able to install the software, restart my computer, and connect to AT&T's 3G network.

The AirCard 881U's software was delightfully easy to use and far more bearable than the ridiculous install. To connect to the 3G network, you need only to open the program and click the Connect button. In a matter of seconds, the modem is up and running and you're free to surf.
I was pleasantly surprised with the speed I experienced while browsing the Web. Simple pages like Google (NSDQ: GOOG).com opened in just a few seconds with 3G connectivity and more complex Web sites like ESPN.com opened about twice as fast as my EDGE-connected cell phone, but about 10 seconds slower than my Wi-Fi connection. All in all, I was getting about 1.0 Mbps on the downlink and roughly 375 kbps up.
Although 3G connectivity with the AirCard 881U was a great experience, it suffers from the same limitations that all USB modems do: it's governed by the data coverage that wireless carriers provide. And unless you live in a big city or around a densely populated area, don't expect 3G wherever you go. In fact, I quickly found myself surfing at EDGE speeds when I ventured away from the metro area.
The Sierra Wireless AirCard 881U is a generally lackluster USB modem that's bloated, too heavy, and more of an eyesore than anything else. And although connecting to 3G was delightfully easy and the price tag -- free after mail-in rebate -- is attractive, AT&T's $60 per month data plan and the AirCard 881U's aforementioned issues should make you think twice before picking it up.
source: www.informationweek.com

Sierra Wireless 875U HSDPA USB Modem

by:Sascha Segan
Blaze across the virtual globe with the Sierra AirCard 875U, the fastest, most flexible way to connect your laptop PC to AT&T's high-speed network and to dozens of other computer systems in foreign lands. High-speed wireless connection solutions are available from three major carriers, in four different forms. You can get them from Sprint, Verizon, or AT&T, and they come either as chips embedded in laptops, as PC Cards, ExpressCards, or USB dongles.
USB dongles such as the AirCard 875U are less compact than the other options, but they're a lot more flexible. Since pretty much every PC has a USB port, it's easy to move them between computers. The 875U's SIM card slot is also relatively easy to access under its front cover. This lets you move your SIM between the dongle and your phone more readily than you could with a card.
About the size of an old-school pager, the 875U has a USB jack that pops out of the modem's body on an easy-to-release latch. Plugged into your laptop, it sits upright like a periscope, with unobtrusive green power and signal lights. There's an easy-to-access external antenna port covered by a little rubber plug on the side.
The 875U operates with AT&T's standard LaptopConnect plans. One option costs $69.99 per month for unlimited use in the U.S., and the other will set you back $139.99 per month for unlimited U.S. data plus 100MB of data overseas, with additional overseas MB $5 each. Those prices are on a par with what's offered by Sprint and Verizon.
AT&T's network, meanwhile, has come a long way since I first looked at it last year. AT&T uses HSDPA technology, which also works in dozens of countries overseas, including most of Western Europe. Over the past year, AT&T has extended its network to most major U.S. cities and metro areas. The current HSDPA spec allows for 3.6-Mbps downloads and 384-Kbps uploads, in theory.
In reality, we got average speeds of just over a megabit for downloads on the 875U, with download speeds peaking at 1.63 Mbps. Uploads averaged 275 Kbps, but with a strong signal frequently hovered around 350 Kbps. That's broadband speed, although if you're used to wired or Wi-Fi broadband, you'll still feel that Web pages load slowly because of the average 240-millisecond latency on network requests. The 875U supports the 850, 1800, 1900, and 2100-MHz bands, so you'll be able to get access in Buffalo or Berlin, provided you're on the right service plan.
When the 875U isn't in 3G range, it drops down to AT&T's EDGE network, which offers speeds of around 80 to 120 Kbps down. I generally don't recommend EDGE cards for laptop users for a different reason—EDGE transmissions tend to make some laptop speakers buzz annoyingly. If you're traveling primarily through EDGE country, I'd recommend tethering a phone to your laptop via Bluetooth instead.
The 875U proved faster than the competing AirCard 875 PC Card and Option GT MAX 3.6 Express in head-to-head download tests. It's also faster than older models such as the AirCard 860. The competition was tight. Of 35 downloads, the 875U was the fastest on 15 of them; the ExpressCard was faster on 14 tries. Differences in signal strength between the 875U and the Option ExpressCard were negligible.
Rather, it's the AirCard's flexibility I like. As a USB device, it's easy to plug and unplug at will, and the SIM card slot is easier to extract cards from than on the ExpressCard. Better still, the 875U is compatible with Microsoft Windows XP, Vista, and Mac OS 10.4.9, though its driver isn't integrated into the Mac OS. You have to download a "Sierra AirCard Watcher" application from Sierra's Web site.
source: www.pcmag.com

Huawei E272

he E272 enables uplink speeds of up to 2Mbps and download rates of 7.2 Mbps. Within HSPA network, the device will facilitate fast internet browsing, instant access and the uninterrupted ability both to upload and download data. Combining cutting edge technologies with sleek design, customers can look forward to enjoying high-speed wireless access, both at home and on the go. The plug-and-play featured devices are compatible with Windows (Vista and XP) and Mac OSX, whether run on a PC, laptop or handheld device.

Benefits:
Boost your efficiency with 14 times faster download speeds than standard 3G.
Work more effectively with 22 times faster upload speeds than standard 3G.
Plug and go with any laptop or desktop, including Macs.
Enjoy seamless coverage at home and roaming abroad.
Connect with speeds of up to 7.2Mbps.

Specification:

* The USB Modem works with all laptops including Macs. It can also be used with any PC.

Microsoft Windows requirements:
* Standard USB interface
* Microsoft Windows 2000, XP or Vista
* Microsoft Internet Explorer 5.5 or higher
* At least 50MB free disk space and 128MB RAM

Apple Mac requirements:
* Standard USB interface
* Optimised for Power PC based Macs and Intel based Macs
* Mac OS X Panther 10.3.9 or higher

Technical Specification:
* 3G (UMTS/HSDPA/HSUPA) Frequency supported 2100Mhz
* EDGE/GPRS Frequency supported 900,1800 and 1900Mhz
* Support for USA/Canada :Yes For GPRS/EDGE at 1900MHz

Auto switch frequency: YES
WLAN network supported: NO
Apple Mac compatible: Yes , with special VMC software for Mac OS

source : hkoffer.com

Huawei E220 USB Modem

Been using Huawei E220 for around 1 month, I could say that this modem does its function well. No issue related to hardware. The installation process completed with auto-run in Windows Operating System, no need any installation CD, just plug the modem to any USB port and it will prompt you to start the software installation.
The connection is stable, however it depends on your network provider as well. in my home area, around Pangkalan Jati, Kalimalang. It could run very well for nights and days, without any need of reconnection.
This modem was launched back in 2006. Maximum speed is 3.6 Mbps, you could set this modem to use 3G only signal, or 3G prefered if you are not sure you will get a good reception of 3G signal.
Bought it for Rp.1.450.000 in a store at ITC Kuningan Jakarta, I am surprise to see this modem sold for Rp.1.250.000 at a small computer store in Palembang .
I use this modem along with Telkomsel Flash Unlimited Package which has virtually unlimited capacity but with limited maximum speed of 256Kbps (up to 3Gb per-month, before the speed is reduced to 64Kbps).
Connection of max 256Kbps is quite decent for me, allows me to check web mail, update anti virus, connect to my company VPN - Virtual Private Network, and do some downloads (never yet try to download big files though). However because the speed limitation of Telkom Flash unlimited package, I have never test the maximum speed of this modem.
I have tested this modem along with Telkomsel Flash in area of Kalimalang Jakarta (HSDPA connection - Very Good), Kuningan Jakarta (HSDPA connection - Very Good), Plaju - Palembang (HSDPA connection - not to good, some re-connection needed, sometime could not connect), Tuban - East Java (EDGE connection, but stable).
The whole body of this modem is plastics. There is no lock on the SIM card port, so you need to be careful not to drop this modem to the floor. It might spit out your SIM Card. Also don’t step on it, I believe it will break a part.
If you are a mobile person who need a notebook computer to work and be online, or you need a HSDPA modem which you could use on your home PC and notebook computer; and you just can’t rely on with your HSDPA smartphone for some reasons, I recommends Huawei E220.
source :myweathertop.wordpress.com

NOVATEL OVATION MC930D/MC950D

Nowadays, Internet connectivity ranks high in our hectic everyday schedules, regardless of the fact that we have places to visit, people to meet, and things to get done. It’s not surprising that we’re practically as dependent on the Internet as we are on electricity. Thus, we need absolute on-the-road mobility with universal connectivity. Today we’re going to review Novatel’s Ovation MC950D HSPA mobile broadband USB modem.
The Ovation MC950D is a 3G modem based on the latest HSUPA, HSDPA, and UMTS technologies. HSUPA stands for High-Speed Uplink Packet Access, HSDPA stands for High-Speed Downlink Packet Access, and UMTS represents Universal Mobile Telecommunications System technology. These are key technologies of 3G, which offers the most cutting-edge high performance data access speeds.

resumably, the Ovation MC950D and its younger sister, the MC930D, are the world’s smallest modems. This is possible thanks to their latest innovative design, which is similar to the USB stick form factor standards. It fits comfortably in a pocket. And most importantly, backwards compatibility isn’t neglected because the modem can switch back to quad-band GPRS/EDGE 2G technologies when tri-band UMTS 3G signals aren’t reachable.
The modem supports up to 7.2mbps downlink data access speeds and 2.1mbps uplink. The aforementioned are architectural limitations by design because these speeds are 100% dependent on carriers and network operators. This gadget doesn’t bring you the Internet “for free;” you need to sign up with a carrier for a plan or account in your area, and then you receive an UMTS HSUPA/HSDPA compatible SIM card.
Novatel Wireless optimized this modem for North America, Europe, and Japan, but technically worldwide support is possible as long as there is the necessary network coverage on the supported bands. It is platform independent so it works fine on Microsoft Windows, MAC OSX, UNIX, and Linux operating systems.
There are lots of network partners that are selling the Ovation MC950D modem. More often than not, these partners are network operators and, therefore, you can also sign up with them right away. For this review, the modem was acquired through Vodafone so it sports the “Vodafone” logo instead of Novatel Wireless. The red SIM card is also from Vodafone.
Nevertheless, we can’t continue before examining its price. The Ovation MC950D is available for around £159.80, €210, and US$320 at the time of writing. Sure, it’s not a bargain, but you need to pay the price for innovation and universal connectivity. Additionally, the plans can go up to €30 per month, but mostly this depends on features - whether it’s unlimited or not, your area, how the network looks there, etc.
source : www.devhardware.com

Sierra Wireless' Compass 597

Unlike its older brother, the AirCard 881U, the Sierra Wireless Compass 597 is an attractive addition to any computer. Better yet, the company's smallest USB modem offers a fully equipped device that easily outshines other Sierra Wireless products and competes admirably with the Novatel USB727. And with a beautiful black finish and an attractive light on the end to tell you it's in use, you won't be put off by this modem's looks.
The Compass 597's installation on my MacBook was quick and easy. In a matter of seconds, I popped the modem into my computer, installed the software, restarted my computer, and connected toSprint (NYSE: S)'s Mobile Broadband Network without a hiccup. Much like the Novatel USB727, the installation process was seamless. But no disc was required to install the software. Instead, the Compass 597 has all drivers and software already installed on it, which speeds and simplifies installation.
While connected to Sprint's Mobile Broadband Network, Google loaded quickly and detailed sites like ESPN popped up at an adequate, but noticeably slower speed than the load times I witnessed on Verizon's BroadbandAccess and AT&T's 3G network. According to Speedtest.net, I achieved speeds of about 875 kbps down and 300 kbps up.
The Compass 597 uses Sprint's SmartView software, which is easily the best package on the market and much better than the tools I used on the other modems. Aside from GPS tracking and the ability to search points of interest in your area, the tool also allows you to test upload and download times, get an updated view of Sprint's Broadband coverage map, manage your Sprint account, and access the company's Digital Lounge service.
Sprint's Digital Lounge allows you to buy anything from screensavers for your phone, to music, TV, and games. Even though most of the content is too expensive to justify a purchase, it's nice to have the option.
The Sierra Wireless Compass 597 is a fine USB modem that won't take up too much room in your pocket, nor look too foolish hanging off the side of your computer. And with a fantastic software package, it's not a bad idea to pick this one up -- if you don't mind spending $100 (after rebate) for the modem plus $60 per month for 5 GB of data.
source : www.informationweek.com

VODAFONE HUAWEI E172

Vodafone has partnered with Chinese telecoms equipment maker Huawei to create a USB 3G modem the size of a flash drive, but still capable of accessing HSUPA mobile data networks.

The mobile broadband USB modem stick, the Huawei E172, is Vodafone's smallest ever plug-and-play device and significantly smaller than any previous data card or 3G modem it has offered. It is compatible with Windows (Vista and XP) as well as Mac OS X.

Vodafone will offer the stick alongside its existing, E220 USB modem which was released last year. "They are exactly the same inside," said Vodafone spokeswoman Bryony Clow. "It's just that the E172 has a smaller form factor. We are looking to sell both as the different forms will appeal to different people. We'll be pushing the stick, but the modem will be available as well."

The E172 supports uplink speeds of up to 1.44Mb/sec and download rates of 7.2 Mb/sec, which they claim is theoretically 14 times the speed of standard 3G. However, the 7.2Mb service is currently only supported within Central London and at certain UK airports. This will increase as Vodafone continues the rollout of HSUPA to the rest of its 3G network.

"Vodafone was the first to improve download speeds with HSPDA, the first to increase upload speeds with HSPUA. And now we're pushing the boundaries of usability even further with a compact modem design," said Kyle Whitehill, enterprise director at Vodafone.

The mobile broadband market is getting more competitive, with network operators cutting prices and adding value to service plans to entice both consumer and business customers. Last week IT PRO reported that Carphone Warehouse and mobile network 3 had joined forces to offer a £35-a-month bundle comprising a mobile broadband service, bundled text messages and a Dell laptop.
source :www.itpro.co.uk

Guide to GSM, GPRS, 3G, EDGE, HSDPA

2009-01-14T21:02:00.001-08:00

It can be confusing trying to understand the differences between the various mobile connectivity options listed in the specifications of smartphones and touted by the mobile networks as the best way to connect to the internet. In this guide we will try to summarise these technologies and point out the advantages and disadvantages of each technology.

GSM

GSM (Global system for mobile communications) is the standard by which the vast majority of mobile handsets work in Europe and is becoming dominant in other parts of the world with over 2 billion people currently using the system. When you purchase a mobile or smartphone it is important to understand what frequencies are used by each technology because manufacturers and networks have a tendency to quote these figures with little explanation as to what they mean.

The majority of GSM networks use 900MHz and 1800MHz but in the US the 850MHz and 1900Mhz are prominent. If these are quoted the phone will be classed as a tri-band phone and can be used in Europe, the US and many other territories (provided your SIM is enabled). If you require mobile access in the Far East and areas such as Scandanavia you will need to check with your mobile provider because at the minimum a quad-band phone will be required and in some areas only a phone purchased in the country will work.

Most GSM phones are primarily used for voice but can be used for mobile internet access via the GPRS Core Network.

GPRS

GPRS is a system used to transmit data at speeds of up to 60 kbits per second and is a battery friendly way to send and receive emails and to browse the internet but in these days of broadband connectivity it will be seen as slow by some. To set up GPRS connections on your smartphone you will need to obtain specific information from your mobile provider to input into your phone. Most are happy to provide this information and some manufacturers such as Nokia offer pre-configured files that you can install onto your phone for your network.

GPRS is a tried and tested system and is therefore very reliable for standard mobile data use and will suit people with moderate data needs. Once you have the required settings in place you can use the network whenever you like and it requires no further adjustment as it works in the background of your internet enabled applications.

EDGE

EDGE (Exchanged Data rates for GSM Evolution) is a recent development based on the GPRS system and has been classified as a '3G' standard due to the fact that it can run at up to 473.6 kbits per second. If a smartphone is EDGE compliant it can be used for heavy mobile data transmission such as receiving large email attachments and browsing complex web pages at great speed. To use EDGE cell sites must be modified to accept transmissions of this type so coverage can be patchy in certain areas- it is a technology well worth having built in to any smartphone though.

3G was initially marketed as a way to make video calls on the mobile network but is also a highly efficient way of browsing the internet and communicating on your smartphone using voice over IP and by email and instant messaging. Most UK and some European networks now have 3G networks and with speeds similar to EDGE it is fast becoming a common way to connect while on the road.

In areas where 3G coverage is poor the handset will constantly try to find a 3G signal and this can have a dramatic affect on battery life. Some phones handle constant 3G enablement well but some can have their battery life reduced by up to 50% so it is worth checking that your potential purchase is able to cope with this. At this time though 3G has good coverage and enables high speed internet access from your phone and is fast becoming a standard for mobile connectivity.

HSDPA

HSDPA (High speed Downlink Packet Access) is a technology based on the 3G network which can support speeds of up to 7.2 mbits per second. In reality you will most likely get a top speed of around 3 mbits but this is useful for mobile TV streaming and other high end data transmissions. To use HSDPA your phone must be able to support the technology and of course you will need to be located within range of a cell site that has been upgraded to offer the service.

The key to all of these technologies is to understand what your typical usage will be and which of the above suit your needs. It could also be worth future proofing your needs because well connected devices often cost little more than phones with basic connectivity.

source : www.clove.co.uk

2.5G, 3G, 3.5G and 4G technology

2009-01-14T20:22:00.000-08:00

What is 4G?

4G takes on a number of equally true definitions, depending on who you are talking to. In simplest terms, 4G is the next generation of wireless networks that will replace 3G networks sometimes in future. In another context, 4G is simply an initiative by academic R&D labs to move beyond the limitations and problems of 3G which is having trouble getting deployed and meeting its promised performance and throughput. In reality, as of first half of 2002, 4G is a conceptual framework for or a discussion point to address future needs of a universal high speed wireless network that will interface with wireline backbone network seamlessly. 4G is also represents the hope and ideas of a group of researchers in Motorola, Qualcomm, Nokia, Ericsson, Sun, HP, NTT DoCoMo and other infrastructure vendors who must respond to the needs of MMS, multimedia and video applications if 3G never materializes in its full glory.

Motivation for 4G Research Before 3G Has Not Been Deployed?

3G performance may not be sufficient to meet needs of future high-performance applications like multi-media, full-motion video, wireless teleconferencing. We need a network technology that extends 3G capacity by an order of magnitude.

There are multiple standards for 3G making it difficult to roam and interoperate across networks. we need global mobility and service portability

3G is based on primarily a wide-area concept. We need hybrid networks that utilize both wireless LAN (hot spot) concept and cell or base-station wide area network design.

We need wider bandwidth

Researchers have come up with spectrally more efficient modulation schemes that can not be retrofitted into 3G infrastructure

We need all digital packet network that utilizes IP in its fullest form with converged voice and data capability.

Comparing Key Parameters of 4G with 3G

	3G (including 2.5G, sub3G)	4G
Major Requirement Driving Architecture	Predominantly voice driven - data was always add on	Converged data and voice over IP
Network Architecture	Wide area cell-based	Hybrid - Integration of Wireless LAN (WiFi, Bluetooth) and wide area
Speeds	384 Kbps to 2 Mbps	20 to 100 Mbps in mobile mode
Frequency Band	Dependent on country or continent (1800-2400 MHz)	Higher frequency bands (2-8 GHz)
Bandwidth	5-20 MHz	100 MHz (or more)
Switching Design Basis	Circuit and Packet	All digital with packetized voice
Access Technologies	W-CDMA, 1xRTT, Edge	OFDM and MC-CDMA (Multi Carrier CDMA)
Forward Error Correction	Convolutional rate 1/2, 1/3	Concatenated coding scheme
Component Design	Optimized antenna design, multi-band adapters	Smarter Antennas, software multiband and wideband radios
IP	A number of air link protocols, including IP 5.0	All IP (IP6.0)

What is needed to Build 4G Networks of Future?

A number of spectrum allocation decisions, spectrum standardization decisions, spectrum availability decisions, technology innovations, component development, signal processing and switching enhancements and inter-vendor cooperation have to take place before the vision of 4G will materialize. We think that 3G experiences - good or bad, technological or business - will be useful in guiding the industry in this effort. We are bringing to the attention of professionals in telecommunications industry following issues and problems that must be analyzed and resolved:

Lower Price Points Only Slightly Higher than Alternatives - The business visionaries should do some economic modeling before they start 4G hype on the same lines as 3G hype. They should understand that 4G data applications like streaming video must compete with very low cost wireline applications. The users would pay only a delta premium (not a multiple) for most wireless applications.

More Coordination Among Spectrum Regulators Around the World - Spectrum regulation bodies must get involved in guiding the researchers by indicating which frequency band might be used for 4G. FCC in USA must cooperate more actively with International bodies like ITU and perhaps modify its hands-off policy in guiding the industry. When public interest, national security interest and economic interest (inter-industry a la TV versus Telecommunications) are at stake, leadership must come from regulators. At appropriate time, industry builds its own self-regulation mechanisms.

More Academic Research: Universities must spend more effort in solving fundamental problems in radio communications (especially multiband and wideband radios, intelligent antennas and signal processing.

Standardization of wireless networks in terms of modulation techniques, switching schemes and roaming is an absolute necessity for 4G.

A Voice-independent Business Justification Thinking: Business development and technology executives should not bias their business models by using voice channels as economic determinant for data applications. Voice has a built-in demand limit - data applications do not.

Integration Across Different Network Topologies: Network architects must base their architecture on hybrid network concepts that integrates wireless wide area networks, wireless LANS (IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.15 and IEEE 802.16, Bluetooth with fiber-based Internet backbone. Broadband wireless networks must be a part of this integrated network architecture.

Non-disruptive Implementation: 4G must allow us to move from 3G to 4G.

source : www.mobileinfo.com

Router Review

2009-01-14T16:00:00.000-08:00

This posting discuss about router. Many router product on the world. We never know what the peformance of it. So I compare routers review. The compare product is Linksys WRT56GS, Netgear WGT624, D-Link DI624, Dell Wireless 2300, Microsoft MN-700, and Buffalo AirStation WLA-G54. I hope you can choose the best router after read it.

Linksys WRT54GS

review by: Xiao Ming Wu

Editors' note: The rating and/or Editors' Choice designation for this product has been altered since the review's original publication. The reason for this is simply the general improvement of technology over time. In order to keep our ratings fair and accurate, it's sometimes necessary to downgrade the ratings of older products relative to those of newer products. (12/9/04) The Linksys WRT54GS Wireless-G Broadband Router with SpeedBooster makes it easy to set up a typical home or office network, and it comes with all the documentation you need to get it up and running. It touts a wealth of advanced networking and security features, and it's fast, especially in networks with both 802.11g and 802.11b connections.The illustrated Fast Start guide for the Linksys WRT54GS Wireless-G Broadband Router with SpeedBooster walks you through the basic setup, which includes connecting the router to your computer and broadband modem, configuring all the computers on the network to work with the router, and configuring the router. The Fast Start guide is more thorough than others we've seen, with plenty of images and screenshots illustrating the setup process. We were glad to see brief explanations of basic networking terms, such as the difference between static and dynamic IP addressing and what to do if your DSL provider uses PPPoE. The guide also describes how to connect to the WRT54GS's browser-based configuration tool if you need to tweak the router's configuration--for example, to supply the router with a static IP address. No quick-setup guide can cover all possible networking scenarios, but Linksys's step-by-step guide does an excellent job rounding up the usual suspects and making it easy for most homes and small offices to set up a network in a few minutes. In most cases, you need only to plug in the router and connect the cables. For more complicated setups, Linksys includes a thorough user guide detailing the WRT54GS's diverse features.Although the Linksys WRT54GS Wireless-G Broadband Router with SpeedBooster is easy to set up, you'll find a number of advanced features and configuration options under the hood. The Linksys WRT54GS's browser-based configuration tool gives you access to the router's networking and security settings, such as DHCP server and client settings, firewall settings, and wireless encryption settings. The router also comes with two types of firewalls. One is a Stateful Packet Inspection (SPI) firewall that makes sure packets are part of a legitimate connection; the other is a NAT firewall that effectively hides computers behind the router. You can lock your network down even tighter by configuring the router to block services such as FTP and Telnet. A DMZ function located on the configuration tool's Applications and Gaming tab lets you place one computer outside the firewall, which can be useful for Internet gaming and videoconferencing. The Linksys WRT54GS also lets you set up access-control policies that grant Internet access to specific computers on your network at predetermined times of day and days of the week. If you telecommute, the router's VPN pass-through support will help get you to work. The Linksys WRT54GS router also has good wireless security. You can configure it to use WEP or WPA. WPA is stronger than WEP, but it's important to have both options, because you may want to connect to older 802.11b devices that lack WPA support. We also like that you can turn off the beacon on the WRT54GS's integrated 802.11g access point. This helps protect you from uninvited guests by stopping the access point from advertising its presence to the world. The Linksys WRT54GS router comes with removable antennas, giving you the option of attaching high-gain antennas to the unit to increase its range. Our only gripe was that the router lacks a mounting bracket.The Linksys WRT54GS Wireless-G Broadband Router with SpeedBooster is one of a growing number of wireless routers touting proprietary speed enhancements. Like the D-Link DI-624 and the Netgear WGT624, the WRT54GS SpeedBooster router includes a technology (in this case, Broadcom's Afterburner) that substantially increases wireless network performance. The enhancements kick in only if all the devices on the network are playing by the same proprietary rules; otherwise, the device scales down to standard 802.11g speeds. We think that this limitation makes the SpeedBooster enhancement (and similar Turbo or Super-G offerings from vendors such as D-Link and Netgear) more of a marketing gimmick than a significant feature. Proprietary solutions depend on networks molded out of homogenous gear, limiting your purchase choices and tying you to a single vendor. On the other hand, the Linksys WRT54GS Wireless-G Broadband Router with SpeedBooster does a fine job supporting standards-based equipment from other vendors, even older 802.11b gear. In CNET Labs' mixed-mode tests, which measure throughput when both 802.11g and 802.11b transmissions occur simultaneously, the WRT54GS delivered the fastest speeds we've seen, clocking in at 25.8Mbps. The Linksys also went the distance, stretching as far as 200 feet in our range tests.

Netgear WGT624
review by: Allen Fear

The Netgear WGT624 108Mbps wireless firewall router is a good example of the advantages and disadvantages of bleeding-edge technology. It offers nearly double the throughput of standard 802.11g devices and increased range to boot. Plus, the WGT624's fast throughput over distance combined with its support for portions of the 802.11e draft standard make it well suited for streaming media over your wireless connection. Other advanced features, such as an SPI firewall and support for Dynamic DNS, make the WGT624 a good choice for techies who are looking for a high-performance wireless router and are willing to perform an occasional firmware upgrade. (Netgear has already released one firmware upgrade for the router that fixes some bugs and enhances performance.) If the idea of router maintenance doesn't appeal to you, consider the Dell Wireless 2300, which lacks the speed of the WGT624 but is easier to set up, or the Microsoft MN-700, which automatically checks for firmware upgrades. The Netgear WGT624 108Mbps wireless firewall router comes with all the hardware and software you'll need to set up your network. In addition to the router, the product package contains an AC power adapter, a rubber stand, an Ethernet cable, a printed installation guide, and a CD containing a comprehensive reference manual. We like the compact design of the WGT624. The router's rubber stand and built-in mounting bracket on the bottom panel help you position the device for optimum range. The LEDs on the front of the unit let you monitor data passing across the WGT624's Ethernet and wireless interfaces. Plug the router in, connect it via the Ethernet cable to your broadband modem, and you've installed the WGT624 hardware. The network installation is a little less straightforward, and the printed guide may leave some in the lurch. The guide asks you to manually reconfigure the network settings of each computer if necessary, then it refers you to an online resource to learn how to do this. In contrast, the Dell Wireless 2300 and the Microsoft MN-700 include software that automatically configures the network settings for the router and any connected computers, making these instruments better suited for those new to networking. After you connect the WGT624 to your local network, the router's browser-based Smart Wizard automatically detects the type of Internet service you have and directs you through the rest of the installation. The Netgear WGT624 108Mbps wireless firewall router has a good feature set that meets the needs of both advanced users and those with little or no networking experience. The WGT624's browser-based configuration tool is easy to navigate and offers features tailored for family networking. The tool is password-protected and includes a content-filtering section that gives you control over the types of sites your computers can access, letting you restrict access based on keywords, service types, IP addresses, and times of day. The WGT624 also displays detailed logs of the Web sites that your computers have accessed or attempted to access, which lets you police the types of traffic passing through your network. The router includes two different types of firewalls: network address translation (NAT), which hides your computers' IP addresses behind the router's IP address, and stateful packet inspection (SPI), which checks individual data packets to make sure they are part of a legitimate connection. Together, these firewalls provide strong security against most attacks originating from the Internet. The WGT624 also supports WEP and the stronger WPA encryption scheme. We wish that the WGT624 supported wireless distribution system (WDS). Limited range is a problem for many home networking environments, and WDS makes it easy to expand your coverage area by simply adding a repeater, such as the Buffalo WLA-G54C, to rooms where your signal is weak. The WGT624 has other performance enhancers under the hood that make it especially well suited for streaming media. Portions of the 802.11e draft specification are built into the router's firmware. These new features ensure that streaming media applications, such as the voice and video links in a teleconference, aren't interrupted by a simple file transfer. This means that you can participate in the teleconference over your wireless connection and download data from the Internet without suffering degradation in the audio or video quality of the links. The most noteworthy feature of the Netgear WGT624 108Mbps wireless firewall router is its inclusion of Super G Technology (link is a PDF file), which boosts the router's speed to nearly twice the tempo of standard 802.11g devices'. A recent firmware upgrade allows the router to switch dynamically to support standard 802.11g and 802.11b devices when they enter the network. CNET Labs tested the router's throughput with various adapters concurrently, and the results are impressive. The WGT624 ran circles around the U.S. Robotics USR8054. Better yet, the Netgear router delivered fantastic range in our indoor tests, providing stable connections as far as 225 feet away.

D-Link DI624
Review By: Allen Fear

Editor's note: The rating and/or Editors' Choice designation for this product has been altered since the review's original publication. The reason for this is simply the general improvement of technology over time. In order to keep our ratings fair and accurate, it's sometimes necessary to downgrade the ratings of older products relative to those of newer products. (12/14/04) When we first reviewed the D-Link DI-624 AirPlus Xtreme G router a year ago, we were unimpressed, but that was then, and this is now. The new DI-624 is about half the size of the original and twice as fast. It also comes with an improved quick-installation guide, a more comprehensive manual, stronger security features, and an excellent support package that includes a long, three-year warranty. Few routers are as easy to set up as the DI-624, but if the thought of typing an IP address into your browser's address bar makes you sweat, then consider the less powerful but easier to use, Microsoft MN-700. On the other hand, if you're looking for a fast router with excellent range and a bushel of features, such as a configurable firewall, parental controls, top-notch wireless security, and VPN pass-through support, then look no further. With a current street price of about $70, the DI-624 is a great buy for both home and small office networks. For a router with such an advanced feature set, the D-Link DI-624 AirPlus Xtreme G router is easy to set up. The package includes everything you'll need: the router; a CD-ROM containing a manual and warranty info; an Ethernet cable; and a 5V DC power adapter. The new DI-624 is compact, about the size of a medium-size paperback, and its bottom panel doubles as a mounting bracket, making it easy to attach to a wall or the ceiling. Unfortunately, the DI-624 doesn't come with a stand for vertical positioning, which is a feature we like in the Netgear WGT624. The hardware setup is a snap, literally. Connect the DI-624 to your broadband modem with the cable that came with your modem, use the Ethernet cable in the package to connect the router to your computer, and you're done. Although D-Link doesn't offer an automated configuration routine like the one you'll find with the Dell Wireless 2300 and the Microsoft MN-700, the DI-624's network setup is about as easy as it gets; it's one of the smoothest setup routines we've seen. The printed quick-installation guide walks you through every step of the installation process, with screen shots and instructions for both Mac OS X and Windows XP that show you how to connect to the DI-624's browser-based configuration tool. The browser-based tool itself includes a five-step setup wizard that automatically detects your Internet connection and configures security for your wireless network. The explanations and instructions in the printed quick-installation guide seamlessly complement the wizard, addressing each step in the process. The D-Link DI-624 AirPlus Xtreme G router is chock-full of features for both homes and small offices. Auto MDI/MDIX ports in the router's Ethernet switch eliminate the need for costly crossover cables and make the DI-624 easy to connect to other hubs and switches. The router also comes with a removable antenna, so you can expand your coverage area by adding an antenna. The router also features parental controls that include URL filtering, domain blocking, and access scheduling by day of the week and time of day. If you play games over the Internet, you can use the DI-624's special gaming mode, which adjusts the firewall to allow for network entertainment. For connections that demand even less restrictive access, such as videoconferencing, you can use the router's DMZ feature, which lets you place a single computer outside the router's firewall. If you telecommute, the DI-624 also supports VPN pass-through for both PPTP and IPSec. With a firewall that is more configurable than most we've seen, the DI-624's security is top-notch for a consumer router. You can turn the firewall on and off, a feature missing from the Microsoft MN-700 and one that can be important for troubleshooting and allowing certain types of connections. You can also create a list of rules that let you allow or deny specific types of traffic between your internal network and the Internet. For example, you can block UDP traffic from the Internet targeted for a specific port on one of your computers. The DI-624 heaps on wireless security features. The router supports not only 64- and 128-bit WEP encryption, but also WPA and ironclad 802.1x authentication via a RADIUS server. The D-Link DI-624 AirPlus Xtreme G router is one of the best-performing routers we've seen. Like the Netgear GT624, the D-Link DI-624 comes equipped with an Atheros AR5002 chipset, the secret to its blazing throughput and great range. If you already have a DI-624, you can upgrade the router's firmware to the latest version to take advantage of the new performance enhancements. The so-called 108Mbps firmware is currently available only for DI-624s with a label on the bottom that reads "H/W Ver.:C1." At close range, the DI-624 clocked in at 44.4Mbps. That's about twice as fast as a typical 802.11g router and just under the Netgear WGT624's speed of 47.1Mbps. The DI-624 also matched the WGT624 in range, surpassing other 802.11g performers with a record-setting 225 feet. We were less impressed with the DI-624's performance in a mixed environment with 802.11b devices. Here, the router was able to eke out only 11.6Mbps at close range, noticeably less than the 18.2Mbps demonstrated by the Dell Wireless 2300.

Dell Wireless 2300
Rreview By: Patrick Unnold

Editors' note: The rating and/or Editors' Choice designation for this product has been altered since the review's original publication. The reason for this is simply the general improvement of technology over time. In order to keep our ratings fair and accurate, it's sometimes necessary to downgrade the ratings of older products relative to those of newer products. Dell's Wireless 2300 broadband router offers superior performance and a well-rounded feature set suited for the home user. Windows 2000 and XP users, as well as novices, will like the streamlined installation, which nearly runs itself (other operating systems are supported, but not as seamlessly). The Wireless 2300 supports both 802.11b and 802.11g and touts an excellent array of security options, including WPA, WEP, SSID blocking, stateful packet inspection (SPI) firewall, and parental controls. You can also link the router to two additional Wireless 2300 routers to increase your 802.11g coverage area. This is the most polished 802.11g router we have seen to date. The initial setup of the Wireless 2300 is simple and quick, especially for those with Windows 2000 or XP systems. Inserting the accompanying CD starts the Setup Wizard. After a quick scan of your network, the Setup Wizard automatically configures the settings for both your computer and the Wireless 2300. With the Setup Wizard making all of the networking changes for us, we connected quickly and were surfing within just a few minutes. The process takes a bit longer with other OSs, but the included user guide walks you through the process. Changing the router's configuration requires the Web-based configuration tool; unfortunately, it's a little convoluted. For example, the Setup Wizard warns you to lock down the wireless network by changing the SSID, enabling WEP or WPA, and turning off SSID broadcasts. The first two items are easily found in the Basic section of the configuration tool, but users must make their way to the wireless settings of the Advanced section to turn off SSID broadcasts. The Wireless 2300 is packed with features and security, and it supports 802.11g and boasts an eye-pleasing exterior design. The sleek, silver-and-black chassis has wall-mounts built into its base. The clearly labeled indicator lights show activity for the Internet connection, each of the four ports on the built-in 10/100 switch, and the wireless LAN. The Wireless 2300 offers the latest in security options for wireless networking. It supports the new WPA encryption scheme as well as the older 64/128-bit WEP standard. There's no support for 802.1x authentication, but the router does offer an expansive MAC address feature that can be applied to all clients of the Wireless 2300, whether wired or wireless. Stateful Packet Inspection, NAT, packet filtering, and intruder-detection alerts offer a high level of Internet security. Additional security features include port forwarding, which allows for both a DMZ computer and the forwarding of specific packets to specific computers. The well-rounded parental-control feature lets you block Internet access for specific computers by time of day. You can also limit Internet access completely or restrict it to a list of Web sites. Another great feature is the router's ability to create a wireless bridge with up to two additional Wireless 2300s. This lets it function as a bridge and a repeater, similar to the Buffalo WLA-G54. The Dell Wireless 2300 offers some of the best 802.11g throughput rates we've seen to date, second only to the U.S. Robotics USR8054. In our tests, the throughput rates for 802.11g peaked at 23.5Mbps for 802.11g, and those for mixed-mode (with both 802.11g and 802.11b clients transmitting simultaneously) reached 18.2Mbps. The throughput degradation over distance is also very good. Most notably, both the Wireless 2300 and the USR8054 outperform their competitors in mixed-mode performance by more than a factor of two. The Wireless 2300 has a few limitations. The user guide indicates that the Wireless 2300 can support only 16 wireless clients or 64 NAT clients; in addition, having more than 20 simultaneous users of any type degrades the device's overall performance. Most home users will never stress the Wireless 2300 to this extent, but small offices could begin to hit the performance ceiling if their network grows large enough.

Microsoft MN-700
review by: Patrick Unnold

Microsoft's new 802.11g MN-700 wireless broadband router is designed so that even a novice user can expand a home network easily, but it has a few shortcomings compared to the Editors' Choice-winning Dell TrueMobile 2300. The setup process and the configuration utility are very user-friendly, and Microsoft's support options will help with most problems you might encounter. It offers most features that home users need, and the Setup Wizard automatically turns on wireless security--a unique and much-needed detail. Its range is excellent. Experienced users will be frustrated by the lack of advanced configuration options and wireless bridge support, however. Like the Dell TrueMobile 2300's streamlined installation routine, the MN-700's Setup Wizard gathers the necessary network information automatically before configuring both your wireless network adapter and the MN-700. The Setup Wizard supports all Windows platforms; a nonautomated, browser-based interface is available for other OSs. We uncovered a bug in the Setup Wizard software that prevented the application from completing normally when we attempted to use a workgroup name that contained a period. Microsoft tech support worked quickly to determine the cause and promised a fix in a future release. The MN-700's documentation is excellent. In addition to the printed installation guide, you get a thorough, printed user guide with a lengthy troubleshooting section, as well as detailed instructions for nonstandard installations, such as using the MN-700 as an access point instead of as a router. You use the Broadband Network Utility, which you install on one of your networked machines during setup, to check network status and adjust the MN-700's configuration. Like the Setup Wizard, the Broadband Network Utility is novice-friendly; it's easy to navigate, with clear help information on each screen. The utility also checks automatically for updates, making it simple to keep the firmware current. The MN-700's impressive security setup includes one unique and much-needed touch: wireless security is enabled during setup--no other product we've seen does this--and other security features, such as Stateful Packet Inspection (SPI) firewall and NAT, are always on. Additional security features include parental controls, client filtering, 64/128-bit WEP, 256-bit WPA, DMZ, MAC address filtering, and detailed logging. While the MN-700 boasts 802.11b/g Wi-Fi certification and an impressive feature set for home users, it doesn't offer much advanced configurability. For instance, it lacks options such as support for RADIUS and wireless bridging, which are available on similarly priced products, such as the Buffalo AirStation router. Also, you cannot control the output wattage for the wireless network or adjust the security level of the firewall. The only option available for configuring the firewall is a check box for enabling ICMP blocking. The Dell TM2300 gives you more control of the firewall. The MN-700's hardware features mirror those of most other home routers. The device sports a rotating external antenna and a four-port 10/100 Ethernet switch that autosenses crossover cables as well as the line speed. The MN-700 is designed for the desktop and is not well suited for mounting on a wall or a ceiling. With a healthy throughput of 21Mbps in 802.11g mode and nearly 12Mbps in mixed 802.11b/g mode, the MN-700 outperforms many of the wireless broadband routers we've tested. However, the MN-700 still falls short of the throughput we've seen in the broadband routers released since the 802.11g specification was ratified, specifically the US Robotics 8054 and the Dell TrueMobile 2300. Thanks no doubt to its rotating external antenna, the MN-700 showed solid performance over distance, outperforming even the US Robotics 8054 and the Dell TrueMobile 2300. In our tests, the MN-700 achieved a throughput of nearly 6Mbps at a whopping 175-foot distance in 802.11g mode, and it didn't completely drop off until it approached 200 feet. That gives it about a 25-foot advantage over the Dell and US Robotics products. The extra distance could be important, because unlike the Dell TM2300, the MN-700 cannot be linked via a wireless bridge.

Buffalo AirStation WLA-G54
Reviewed by: Patrick Unnold

A single wireless router or access point can't always cover every room in a house. The Buffalo WLA-G54 wireless bridge gives you a plethora of features and options for expanding your home or office network without stringing cable. It includes a four-port switch for wired clients, and it supports both 802.11b and 802.11g standards. Because it's externally identical to the Buffalo AirStation 54Mbps wireless broadband router we've previously reviewed, it suffers from the same flaws, including limited mounting options and hard-to-see LEDs for the four-port switch. The Buffalo WLA-G54 installs easily to a wired network, but connecting it to another Buffalo AirStation to create a bridge is harder than it should be. When you start the initial configuration, you can designate either a wired or wireless connection; the quick-setup guide has decent instructions for both. In either case, you have the option of connecting to the WLA-G54 via the Client Manager software included on the CD-ROM or a browser such as Internet Explorer or Netscape. Once you've connected a computer to the WLA-G54, you're ready to integrate it into your network by assigning IP addresses and the ESS-ID and configuring security options. The browser-based configuration tool includes wizards for WEP settings and MAC address restrictions, plus an advanced-configuration page that gives you direct access to all of your options. If you use the WLA-G54 to create a wireless bridge to another Buffalo AirStation, you must register the MAC address of each Buffalo access point, router, or bridge on your network under the WDS section of the configuration screen. The terse documentation fails to cover this process thoroughly. The Buffalo WLA-G54 wireless bridge distinguishes itself from other bridges, such as the Linksys WET54G, with its Wireless Distribution System (WDS) support. This lets the WLA-G54 act as a wireless repeater with up to six Buffalo WDS-enabled AirStations, such as the Buffalo AirStation router on a single network, making it an ideal solution for large houses or apartment buildings. Because WDS is not a standard, however, it doesn't work with non-Buffalo products. A swivel cover on the top of the back panel conceals an MMX connector. For larger sites, the WLA-G54 also works as a point-to-point or point-to-multipoint bridge that's capable of communicating with up to six other Buffalo base stations--a quick, easy way to extend your wired network or improve your existing WLAN coverage. The WLA-G54 is packed with the latest security options to lock down your network. It offers both 64- and 128-bit WEP encryption, but the WLA-G54 also supports WPA and 802.1x. Remembering some of the WLA-G54's more complicated settings is easy because the bridge lets you save its configuration on a local PC. This feature, along with the recessed reset/initialization button on the back of the WLA-G54 that resets it to factory defaults, is very handy in case you find yourself locked out of the device. The only feature we didn't like were the unit's LEDs, which are positioned on the bridge's side and difficult to see. The performance of your Buffalo WLA-G54 will depend greatly on how you've configured it and what it is doing on your network. As an 802.11g access point, the WLA-G54 offers good range, with consistent and decent throughput up to around 100 feet before a swift decline. The Linksys WET54G performs better, but the WLA-G54 offers WDS, which the WET54G lacks. Assume a throughput hit when you configure the WLA-G54 (or most any wireless bridge) as both a bridge and an access point for wireless clients. That's because in a bridged network, configuration packets have to be transmitted over the WLAN once to get to the WLA-G54 bridge, then again from the bridge to the next Buffalo AirStation or client adapter connected to your wireless network.

source:www.review.cnet.com

Introduction Linux Networking

2009-01-13T12:26:00.000-08:00

Now that you have a firm grasp of many of the most commonly used networking concepts, it is time to apply them to the configuration of your server. Some of these activities are automatically covered during a Linux installation, but you will often find yourself having to know how to modify these initial settings whenever you need to move your server to another network, add a new network interface card or use an alternative means of connecting to the Internet.

In "Introduction to Networking", we started with an explanation of TCP/IP, so we'll start this Linux networking chapter with a discussion on how to configure the IP address of your server.

How to Configure Your NIC's IP Address

You need to know all the steps needed to configure IP addresses on a NIC card. Web site shopping cart applications frequently need an additional IP address dedicated to them. You also might need to add a secondary NIC interface to your server to handle data backups. Last but not least, you might just want to play around with the server to test your skills.

This section shows you how to do the most common server IP activities with the least amount of headaches.
Determining Your IP Address

Most modern PCs come with an Ethernet port. When Linux is installed, this device is called eth0. You can determine the IP address of this device with the ifconfig command.

[root@bigboy tmp]# ifconfig -a

eth0 Link encap:Ethernet HWaddr 00:08:C7:10:74:A8
BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:11 Base address:0x1820

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:787 errors:0 dropped:0 overruns:0 frame:0
TX packets:787 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:82644 (80.7 Kb) TX bytes:82644 (80.7 Kb)

wlan0 Link encap:Ethernet HWaddr 00:06:25:09:6A:B5
inet addr:192.168.1.100 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:47379 errors:0 dropped:0 overruns:0 frame:0
TX packets:107900 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:4676853 (4.4 Mb) TX bytes:43209032 (41.2 Mb)
Interrupt:11 Memory:c887a000-c887b000

wlan0:0 Link encap:Ethernet HWaddr 00:06:25:09:6A:B5
inet addr:192.168.1.99 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:11 Memory:c887a000-c887b000

[root@bigboy tmp]#

In this example, eth0 has no IP address because this box is using wireless interface wlan0 as its main NIC. Interface wlan0 has an IP address of 192.168.1.100 and a subnet mask of 255.255.255.0

You can see that this command gives good information on the interrupts, or PCI bus ID, used by each card. On very rare occasions you might find that your NIC card doesn't work because it shares both an interrupt and memory access address with some other device. You can look at the contents of the /proc/interrupts file to get a listing of all the interrupt IRQs used by your system. In the example below we can see that there are no conflicts with each IRQ from 0 to 15 having only a single entry. Devices eth0 and eth1 use interrupts 10 and 5, respectively:

[root@bigboy tmp]# cat /proc/interrupts
CPU0
0: 2707402473 XT-PIC timer
1: 67 XT-PIC i8042
2: 0 XT-PIC cascade
5: 411342 XT-PIC eth1
8: 1 XT-PIC rtc
10: 1898752 XT-PIC eth0
11: 0 XT-PIC uhci_hcd
12: 58 XT-PIC i8042
14: 5075806 XT-PIC ide0
15: 506 XT-PIC ide1
NMI: 0
ERR: 43
[root@bigboy tmp]#

If there are conflicts, you might need to refer to the manual for the offending device to try to determine ways to either use another interrupt or memory I/O location.
Changing Your IP Address

If you wanted, you could give this eth0 interface an IP address using the ifconfig command.

[root@bigboy tmp]# ifconfig eth0 10.0.0.1 netmask 255.255.255.0 up

The "up" at the end of the command activates the interface. To make this permanent each time you boot up you'll have to add this command in your /etc/rc.local file which is run at the end of every reboot.

Fedora Linux also makes life a little easier with interface configuration files located in the /etc/sysconfig/network-scripts directory. Interface eth0 has a file called ifcfg-eth0, eth1 uses ifcfg-eth1, and so on. You can place your IP address information in these files, which are then used to auto-configure your NICs when Linux boots. See Figure 3-1 for two samples of interface eth0. One assumes the interface has a fixed IP address, and the other assumes it requires an IP address assignment using DHCP.

Figure 3-1 - File formats for network-scripts
Fixed IP Address

[root@bigboy tmp]# cd /etc/sysconfig/network-scripts
[root@bigboy network-scripts]# cat ifcfg-eth0

#
# File: ifcfg-eth0
#
DEVICE=eth0
IPADDR=192.168.1.100
NETMASK=255.255.255.0
BOOTPROTO=static
ONBOOT=yes
#
# The following settings are optional
#
BROADCAST=192.168.1.255
NETWORK=192.168.1.0

[root@bigboy network-scripts]#

Getting the IP Address Using DHCP

[root@bigboy tmp]# cd /etc/sysconfig/network-scripts
[root@bigboy network-scripts]# cat ifcfg-eth0

#
# File: ifcfg-eth0
#
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes

[root@bigboy network-scripts]#

As you can see eth0 will be activated on booting, because the parameter ONBOOT has the value yes and not no. You can read more about netmasks and DHCP in "Introduction to Networking", that acts as an introduction to networking.

The default RedHat/Fedora installation will include the broadcast and network options in the network-scripts file. These are optional.

After you change the values in the configuration files for the NIC you have to deactivate and activate it for the modifications to take effect. The ifdown and ifup commands can be used to do this:

[root@bigboy network-scripts]# ifdown eth0
[root@bigboy network-scripts]# ifup eth0

Your server will have to have a default gateway for it to be able to communicate with the Internet. This will be covered later in the chapter.
How DHCP Affects the DNS Server You Use

Your DHCP server not only supplies the IP address your Linux box should use, but also the desired DNS servers. When using DHCP for an interface, make sure your /etc/resolv.conf file has the servers configuration lines commented out to prevent any conflicts.
Multiple IP Addresses on a Single NIC

In the previous section "Determining Your IP Address" you may have noticed that there were two wireless interfaces: wlan0 and wlan0:0. Interface wlan0:0 is actually a child interface wlan0, a virtual subinterface also known as an IP alias. IP aliasing is one of the most common ways of creating multiple IP addresses associated with a single NIC. Aliases have the name format parent-interface-name:X, where X is the sub-interface number of your choice.

The process for creating an IP alias is very similar to the steps outlined for the real interface in the previous section, "Changing Your IP Address":

* First ensure the parent real interface exists
* Verify that no other IP aliases with the same name exists with the name you plan to use. In this we want to create interface wlan0:0.
* Create the virtual interface with the ifconfig command

[root@bigboy tmp]# ifconfig wlan0:0 192.168.1.99 netmask 255.255.255.0 up

* You should also create a /etc/sysconfig/network-scripts/ifcfg-wlan0:0 file so that the aliases will all be managed automatically with the ifup and ifdown commands. Here is a sample configuration:

DEVICE=wlan0:0
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.1.99
NETMASK=255.255.255.0

The commands to activate and deactivate the alias interface would therefore be:

[root@bigboy tmp]# ifup wlan0:0
[root@bigboy tmp]# ifdown wlan0:0

Note: Shutting down the main interface also shuts down all its aliases too. Aliases can be shutdown independently of other interfaces.

After completing these four simple steps you should be able to ping the new IP alias from other servers on your network.
IP Address Assignment for a Direct DSL Connection

If you are using a DSL connection with fixed or static IP addresses, then the configuration steps are the same as those outlined earlier. You plug your Ethernet interface into the DSL modem, configure it with the IP address, subnet mask, broadcast address, and gateway information provided by your ISP and you should have connectivity when you restart your interface. Remember that you might also need to configure your DNS server correctly.

If you are using a DSL connection with a DHCP or dynamic IP address assignment, then the process is different. Your ISP will provide you with a PPP authentication over Ethernet (PPPoE) username and password which will allow your computer to login transparently to the Internet each time it boots up. Fedora Linux installs the rp-pppoe RPM software package required to support this.

Note: Unless you specifically request static IP addresses, your ISP will provide you with a DHCP based connection. The DHCP IP address assigned to your computer and/or Internet router will often not change for many days and you may be fooled into thinking it is static.

Downloading and installing RPMs isn't hard. If you need a refresher, "Installing Linux Software", on RPMs, covers how to do this in detail. When searching for the file, remember that the PPPoE RPM's filename usually starts with the word rp-pppoe followed by a version number like this: rp-pppoe-3.5-8.i386.rpm.

After installing the RPM, you need to go through a number of steps to complete the connection. The PPPOE configuration will create a software-based virtual interface named ppp0 that will use the physical Internet interface eth0 for connectivity. Here's what you need to do:

* Make a backup copy of your ifcfg-eth0 file.

[root@bigboy tmp]#
[root@bigboy tmp]# cd /etc/sysconfig/network-scripts/
[root@bigboy network-scripts]# ls ifcfg-eth0
ifcfg-eth0
[root@bigboy network-scripts]# cp ifcfg-eth0 DISABLED.ifcfg-eth0

* Edit your ifcfg-eth0 file to have no IP information and also to be deactivated on boot time.

DEVICE=eth0
ONBOOT=no

* Shutdown your eth0 interface.

[root@bigboy network-scripts]# ifdown eth0
[root@bigboy network-scripts]#

* Run the adsl-setup configuration script

[root@bigboy network-scripts]# adsl-setup

It will prompt you for your ISP username, the interface to be used (eth0) and whether you want to the connection to stay up indefinitely. We'll use defaults wherever possible.

Welcome to the ADSL client setup.� First, I will run some checks on

your system to make sure the PPPoE client is installed properly...

LOGIN NAME

Enter your Login Name (default root): bigboy-login@isp

INTERFACE

Enter the Ethernet interface connected to the ADSL modem
For Solaris, this is likely to be something like /dev/hme0.
For Linux, it will be ethX, where 'X' is a number.
(default eth0):

Do you want the link to come up on demand, or stay up continuously?
If you want it to come up on demand, enter the idle time in seconds
after which the link should be dropped.� If you want the link to
stay up permanently, enter 'no' (two letters, lower-case.)
NOTE: Demand-activated links do not interact well with dynamic IP
addresses. You might have some problems with demand-activated links.

Enter the demand value (default no):

It will then prompt you for your DNS server information. This step edits your /etc/resolv.conf file. If you're running BIND on your server in a caching DNS mode then you might want to leave this option blank. If you want your ISP to provide the IP address of its DNS server automatically then enter the word server.

Please refer to "Configuring DNS", for more information on BIND and DNS.

DNS

Please enter the IP address of your ISP's primary DNS server.
If your ISP claims that 'the server will provide dynamic DNS addresses', enter 'server' (all lower-case) here.
If you just press enter, I will assume you know what you are doing and not modify your DNS setup.
Enter the DNS information here:

The script will then prompt you for your ISP password

PASSWORD

Please enter your Password:
Please re-enter your Password:

Then it will ask whether you want regular users (not superuser root) to be able to activate/deactivate the new ppp0 interface. This may be required if non-root members of your family or home office need to get access to the Internet:

USERCTRL

Please enter 'yes' (two letters, lower-case.) if you want to allow normal user to start or stop DSL connection (default yes):

The rp-pppoe package has two sample iptables firewall scripts located in the /etc/ppp directory named firewall-standalone and firewall-masq. They are very basic and don't cover rules to make your Linux box a web server, DNS server, or mail server. I'd recommend selecting none and using a variant of the basic script samples in "Linux Firewalls Using iptables", or the more comprehensive one found in Appendix II, "Codes, Scripts, and Configurations".

FIREWALLING

Please choose the firewall rules to use. Note that these rules are very basic. You are strongly
encouraged to use a more sophisticated firewall setup; however, these will provide basic security.
If you are running any servers on your machine, you must choose 'NONE' and set up firewalling
yourself. Otherwise, the firewall rules will deny access to all standard servers like Web, e-mail,
ftp, etc. If you are using SSH, the rules will block outgoing SSH connections which allocate a
privileged source port.

The firewall choices are:

0 - NONE: This script will not set any firewall rules. You are responsible
for ensuring the security of your machine. You are STRONGLY
recommended to use some kind of firewall rules.
1 - STANDALONE: Appropriate for a basic stand-alone web-surfing workstation
2 - MASQUERADE: Appropriate for a machine acting as an Internet gateway
for a LAN

Choose a type of firewall (0-2): 0

You'll then be asked whether you want the connection to be activated upon booting. Most people would say yes.

Start this connection at boot time

Do you want to start this connection at boot time?
Please enter no or yes (default no):yes

Just before exiting, you'll get a summary of the parameters you entered and the relevant configuration files will be updated to reflect your choices when you accept them:

** Summary of what you entered **

Ethernet Interface: eth0

User name: bigboy-login@isp
Activate-on-demand: No
DNS: Do not adjust
Firewalling: NONE
User Control: yes
Accept these settings and adjust configuration files (y/n)? y

Adjusting /etc/sysconfig/network-scripts/ifcfg-ppp0
Adjusting /etc/ppp/chap-secrets and /etc/ppp/pap-secrets
(But first backing it up to /etc/ppp/chap-secrets.bak)
(But first backing it up to /etc/ppp/pap-secrets.bak)

At the very end it will tell you the commands to use to activate /deactivate your new ppp0 interface and to get a status of the interface's condition.

Congratulations, it should be all set up!

Type '/sbin/ifup ppp0' to bring up your xDSL link and '/sbin/ifdown ppp0'to bring it down.
Type '/sbin/adsl-status /etc/sysconfig/network-scripts/ifcfg-ppp0' to see the link status.

Note: This example recommends using the adsl-status command with the name of the PPPoE interface configuration file. This command defaults to show information for interface ppp0, and therefore listing the ifcfg-ppp0 filename won't be necessary in most home environments.

After you have completed installing rp-pppoe you should be able to access the Internet over your DHCP DSL connection as expected.

Some Important Files Created By adsl-setup

The adsl-setup script creates three files that will be of interest to you. The first is the ifcfg-ppp0 file with interface's link layer connection parameters

[root@bigboy network-scripts]# more ifcfg-ppp0
USERCTL=yes
BOOTPROTO=dialup
NAME=DSLppp0
DEVICE=ppp0
TYPE=xDSL
ONBOOT=yes
PIDFILE=/var/run/pppoe-adsl.pid
FIREWALL=NONE
PING=.
PPPOE_TIMEOUT=20
LCP_FAILURE=3
LCP_INTERVAL=80
CLAMPMSS=1412
CONNECT_POLL=6
CONNECT_TIMEOUT=60
DEFROUTE=yes
SYNCHRONOUS=no
ETH=eth0
PROVIDER=DSLppp0
USER= bigboy-login@isp
PEERDNS=no
[root@bigboy network-scripts]#

The others are the duplicate /etc/ppp/pap-secrets and /etc/ppp/chap-secrets files with the username and password needed to login to your ISP:

[root@bigboy network-scripts]# more /etc/ppp/pap-secrets
# Secrets for authentication using PAP
# client server secret IP addresses
"bigboy-login@isp" * "password"
[root@bigboy network-scripts]#

Simple Troubleshooting

You can run the adsl-status command to determine the condition of your connection. In this case the package has been installed but the interface hasn't been activated.

[root@bigboy tmp]# adsl-status
Note: You have enabled demand-connection; adsl-status may be inaccurate.
adsl-status: Link is attached to ppp0, but ppp0 is down
[root@bigboy tmp]#

After activation, the interface appears to work correctly.

[root@bigboy tmp]# ifup ppp0
[root@bigboy tmp]# adsl-status
adsl-status: Link is up and running on interface ppp0
ppp0: flags=8051 mtu 1462 inet
...
...
[root@bigboy tmp]#

For further troubleshooting information you can visit the Web site of rp-ppoe at Roaring Penguin (www.roaringpenguin.com). There are some good tips there on how to avoid problems with VPN clients.
IP Address Assignment for a Cable Modem Connection

Cable modems use DHCP to get their IP addresses so you can configure your server's Ethernet interface accordingly.
How to Activate/Shut Down Your NIC

The ifup and ifdown commands can be used respectively to activate and deactivate a NIC interface. You must have an ifcfg file in the /etc/sysconfig/network-scripts directory for these commands to work. Here is an example for interface eth0:

[root@bigboy tmp]# ifdown eth0
[root@bigboy tmp]# ifup eth0

How to View Your Current Routing Table

The netstat -nr command will provide the contents of the touting table. Networks with a gateway of 0.0.0.0 are usually directly connected to the interface. No gateway is needed to reach your own directly connected interface, so a gateway address of 0.0.0.0 seems appropriate. The route with a destination address of 0.0.0.0 is your default gateway.

* In this example there are two gateways, the default and one to 255.255.255.255 which is usually added on DHCP servers. Server bigboy is a DHCP server in this case.

[root@bigboy tmp]# netstat -nr

Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
255.255.255.255 0.0.0.0 255.255.255.255 UH 40 0 0 wlan0
192.168.1.0 0.0.0.0 255.255.255.0 U 40 0 0 wlan0
127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo
0.0.0.0 192.168.1.1 0.0.0.0 UG 40 0 0 wlan0
[root@bigboy tmp]#

* In this example, there are multiple gateways handling traffic destined for different networks on different interfaces.

[root@bigboy tmp]# netstat -nr

Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
172.16.68.64 172.16.69.193 255.255.255.224 UG 40 0 0 eth1
172.16.11.96 172.16.69.193 255.255.255.224 UG 40 0 0 eth1
172.16.68.32 172.16.69.193 255.255.255.224 UG 40 0 0 eth1
172.16.67.0 172.16.67.135 255.255.255.224 UG 40 0 0 eth0
172.16.69.192 0.0.0.0 255.255.255.192 U 40 0 0 eth1
172.16.67.128 0.0.0.0 255.255.255.128 U 40 0 0 eth0
172.160.0 172.16.67.135 255.255.0.0 UG 40 0 0 eth0
172.16.0.0 172.16.67.131 255.240.0.0 UG 40 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo
0.0.0.0 172.16.69.193 0.0.0.0 UG 40 0 0 eth1
[root@bigboy tmp]#

How to Change Your Default Gateway

Your server needs to have a single default gateway. DHCP servers will automatically assign a default gateway to DHCP configured NICs, but NICs with configured static IP addresses will need to have a manually configured default gateway. This can be done with a simple command. This example uses a newly installed wireless interface called wlan0, most PCs would be using the standard Ethernet interface eth0.

[root@bigboy tmp]# route add default gw 192.168.1.1 wlan0

In this case, make sure that the router/firewall with IP address 192.168.1.1 is connected to the same network as interface wlan0!

Once done, you'll need to update your /etc/sysconfig/network file to reflect the change. This file is used to configure your default gateway each time Linux boots.

NETWORKING=yes
HOSTNAME=bigboy
GATEWAY=192.168.1.1

Note: In Debian based systems the default gateway is permanently defined in the /etc/network/interfaces file. See the section "Debian / Ubuntu Network Configuration" later in this chapter for more details.

Some people don't bother modifying network specific files and just place the route add command in the script file /etc/rc.d/rc.local which is run at the end of each reboot.

It is possible to define default gateways in the NIC configuration file in the /etc/sysconfig/network-scripts directory, but you run the risk of inadvertently assigning more than one default gateway when you have more than one NIC. This could cause connectivity problems. If one of the default gateways has no route to the intended destination, every other packet will become lost. Firewalls that are designed to block packets with irregular sequence numbers and unexpected origins could also obstruct your data flow.
How to Configure Two Gateways

Some networks may have multiple router/firewalls providing connectivity. Here's a typical scenario:

* You have one router providing access to the Internet that you'd like to have as your default gateway (see the default gateway example earlier)

* You also have another router providing access to your corporate network using addresses in the range 10.0.0.0 to 10.255.255.255. Let's assume that this router has an IP address of 192.168.1.254

The Linux box used in this example uses interface wlan0 for its Internet connectivity. You might be most likely using interface eth0, please adjust your steps accordingly.

There are a number of ways to add this new route.

Adding Temporary Static Routes

The route add command can be used to add new routes to your server that will last till the next reboot. It has the advantage of being univeral to all versions of Linux and is well documented in the man pages. In our example the reference to the 10.0.0.0 network has to be preceded with a -net switch and the subnet mask and gateway values also have to be preceded by the netmask and gw switches respectively.

[root@bigboy tmp]# route add -net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 wlan0

If you wanted to add a route to an individual server, then the "-host" switch would be used with no netmask value. (The route command automatically knows the mask should be 255.255.255.255). Here is an example for a route to host 10.0.0.1.

[root@bigboy tmp]# route add -host 10.0.0.1 gw 192.168.1.254 wlan0

A universal way of making this change persistent after a reboot would be to place this route add command in the file /etc/rc.d/rc.local, which is always run at the end of the booting process.
Adding Permanent Static Routes

In Fedora Linux, permanent static routes are added on a per interface basis in files located in the /etc/sysconfig/network-scripts directory. The filename format is route-interface-name so the filename for interface wlan0 would be route-wlan0.

The format of the file is quite intuitive with the target network coming in the first column followed by the word via and then the gateway's IP address. In our routing example, to set up a route to network 10.0.0.0 with a subnet mask of 255.0.0.0 (a mask with the first 8 bits set to 1) via the 192.168.1.254 gateway, we would have to configure file /etc/sysconfig/network-scripts/route-wlan0 to look like this:

#
# File /etc/sysconfig/network-scripts/route-wlan0
#
10.0.0.0/8 via 192.168.1.254

Note: The /etc/sysconfig/network-scripts/route-* filename is very important. Adding the wrong interface extension at the end will result in the routes not being added after the next reboot. There will also be no reported errors on the screen or any of the log files in the /var/log/ directory.

You can test the new file by running the /etc/sysconfig/network-scripts/ifup-routes command with the interface name as the sole argument. In the next example we check the routing table to see no routes to the 10.0.0.0 network and execute the ifup-routes command, which then adds the route:

[root@bigboy tmp]# netstat -nr

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 wlan0
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 wlan0
[root@bigboy tmp]# ./ifup-routes wlan0
[root@bigboy tmp]# netstat -nr
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 wlan0
10.0.0.0 192.168.1.254 255.0.0.0 UG 0 0 0 wlan0
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 wlan0
[root@bigboy tmp]#

Note: In Debian based systems, permanent static routes are configured using the /etc/network/interfaces file. See the section "Debian / Ubuntu Network Configuration" later in this chapter for more details.
How to Delete a Route

Here's how to delete the routes added in the previous section.

[root@bigboy tmp]# route del -net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 wlan0

The file /etc/sysconfig/network-scripts/route-wlan0 will also have to be updated so that when you reboot the server will not reinsert the route. Delete the line that reads:

10.0.0.0/8 via 192.168.1.254

Changing NIC Speed and Duplex

There is no better Linux investment than the purchase of a fully Linux compatible NIC card. Most Linux vendors will have a list of compatible hardware on their Web sites: read this carefully before you start hooking up you machine to the network. If you can't find any of the desired models in your local computer store, then a model in the same family or series should be sufficient. Most cards will work, but only the fully compatible ones will provide you with error-free, consistent throughput.

Linux defaults to automatically negotiating the speed and duplex of it's NIC automatically with that of the switch to which it is attached. Configuring a switch port to auto-negotiate the speed and duplex often isn't sufficient because there are frequently differences in the implementation of the protocol standard.

Typically, NICs with failed negotiation will work, but this is usually accompanied by many collision type errors being seen on the NIC when using the ifconfig -a command and only marginal performance. Don't limit your troubleshooting of these types of errors to just failed negotiation; the problem could also be due to a bad NIC card, switch port, or cabling.

Using mii-tool

One of the original Linux tools for setting the speed and duplex of your NIC card was the mii-tool command. It is destined to be deprecated and replaced by the newer ethtool command, but many older NICs support only mii-tool so you'll need to be aware of it. Issuing the command without any arguments gives a brief status report, as seen in the next example, with unsupported NICs providing an Operation not supported message. NICs that are not compatible with mii-tool often will still work, but you have to refer to the manufacturer's guides to set the speed and duplex to anything but auto-negotiate.

[root@bigboy tmp]# mii-tool
SIOCGMIIPHY on 'eth0' failed: Operation not supported
eth1: 100 Mbit, half duplex, link ok
[root@bigboy tmp]#

By using the verbose mode -v switch you can get much more information. In this case, negotiation was OK, with the NIC selecting 100Mbps, full duplex mode (FD):

[root@bigboy tmp]# mii-tool -v
eth1: negotiated 100baseTx-FD, link ok
product info: vendor 00:10:18, model 33 rev 2
basic mode: autonegotiation enabled
basic status: autonegotiation complete, link ok
capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
advertising: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
[root@bigboy tmp]#

Setting Your NIC's Speed Parameters with mii-tool

You can set your NIC to force itself to a particular speed and duplex by using the -F switch with any of the following options: 100baseTx-FD, 100baseTx-HD, 10baseT-FD, or 10baseT-HD. Remember that you could lose all network connectivity to your server if you force your NIC to a particular speed/duplex that doesn't match that of your switch:

[root@bigboy tmp]# mii-tool -F 100baseTx-FD eth0

Unfortunately there is no way to set this on reboot permanently except by placing it the command in the /etc/rc.local file to let it be run at the very end of the booting process or by creating your own startup script if you need it set earlier. Creating your own startup scripts is covered in "The Linux Boot Process".
Using ethtool

The ethtool command is slated to be the replacement for mii-tool in the near future and tends to be supported by newer NIC cards.

The command provides the status of the interface you provide as its argument. Here we see interface eth0 not doing autonegotiation and set to a speed of 100 Mbps, full duplex. A list of supported modes is also provided at the top of the output.

[root@bigboy tmp]# ethtool eth0
Settings for eth0:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Advertised auto-negotiation: No
Speed: 100Mb/s
Duplex: Full
Port: MII
PHYAD: 1
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: g
Wake-on: g
Current message level: 0x00000007 (7)
Link detected: yes
[root@bigboy tmp]#

Setting Your NIC's Speed Parameters with ethtool

Unlike mii-tool, ethtool settings can be permanently set as part of the interface's configuration script with the ETHTOOL_OPTS variable. In our next example, the settings will be set to 100 Mbps, full duplex with no chance for auto-negotiation on the next reboot:

#
# File: /etc/sysconfig/network-scripts/ifcfg-eth0
#
DEVICE=eth0
IPADDR=192.168.1.100
NETMASK=255.255.255.0
BOOTPROTO=static
ONBOOT=yes
ETHTOOL_OPTS="speed 100 duplex full autoneg off"

You can test the application of these parameters by shutting down the interface and activating it again with the ifup and ifdown commands. These settings can also be changed from the command line using the -s switch followed by the interface name and its desired configuration parameters.

[root@bigboy tmp]# ethtool -s eth1 speed 100 duplex full autoneg off
[root@bigboy tmp]#

The Linux man pages give more details on other ethtool options, but you can get a quick guide by just entering the ethtool command alone, which provides a quicker summary.

[root@bigboy tmp]# ethtool
...
...
ethtool -s DEVNAME \
[ speed 10|100|1000 ] \
[ duplex half|full ] \
[ port tp|aui|bnc|mii|fibre ] \
...
...
[root@bigboy tmp]#

A Note About Duplex Settings

By default, Linux NICs negotiate their speed and duplex settings with the switch. This is done by exchanging electronic signals called Fast Link Pulses (FLP). When the speed and duplex are forced to a particular setting the FLPs are not sent. When a NIC is in auto-negotiation mode and detects a healthy, viable link but receives no FLPs, it errs on the side of caution and sets its duplex to half-duplex and sometimes it will also set its speed to the lowest configurable value. It is therefore possible to force a switch port to 100 Mbps full duplex, but have the auto-negotiating server NIC set itself to 100Mbps half-duplex which will result in errors. The same is true for the switch if the switch port is set to auto-negotiate and server NIC is set to 100 Mbps full duplex. It is best to either force both the switch port and server NIC to either auto-negotiate or the same forced speed and duplex values.
How to Convert Your Linux Server into a Simple Router

Router/firewall appliances that provide basic Internet connectivity for a small office or home network are becoming more affordable every day, but when budgets are tight you might seriously want to consider modifying an existing Linux server to do the job.

Details on how to configure Linux firewall security are covered in "Linux Firewalls Using iptables", but you need to understand how to activate routing through the firewall before it can become a functioning networking device.

Configuring IP Forwarding

For your Linux server to become a router, you have to enable packet forwarding. In simple terms packet forwarding enables packets to flow through the Linux box from one network to another. The Linux kernel configuration parameter to activate this is named net.ipv4.ip_forward and can be found in the file /etc/sysctl.conf. Remove the "#" from the line related to packet forwarding.

Before:

# Disables packet forwarding
net.ipv4.ip_forward=0

After:

# Enables packet forwarding
net.ipv4.ip_forward=1

This enables packet forwarding only when you reboot at which time Linux will create a file in one of the subdirectories of the special RAM memory-based /proc filesystem. To activate the feature immediately you have to force Linux to read the /etc/sysctl.conf file with the sysctl command using the -p switch. Here is how it's done:

[root@bigboy tmp] sysctl -p
sysctl -p
net.ipv4.ip_forward = 1
net.ipv4.conf.default.rp_filter = 1
kernel.sysrq = 0
kernel.core_uses_pid = 1
[root@bigboy tmp]#

Please refer to Appendix I for more information on adjusting kernel parameters.

Configuring Proxy ARP

If a server needs to send a packet to another device on the same network, it sends out an ARP request to the network asking for the MAC address of the other device.

If the same server needs to send a packet to another device on a remote network the process is different. The server first takes a look at its routing table to find out the IP address of the best router on its network that will be able to relay the packet to the destination. The server then sends an ARP request for the MAC address that matches the router's IP address. It then sends the packet to the router using the router's MAC address and a destination IP address of the remote server.

If there is no suitable router on its network, the server will then send out an ARP request for the MAC address of the remote server. Some routers can be configured to answer these types of ARP requests for remote networks. This feature is called proxy ARP. There are some disadvantages with this. One of the most common problems occurs if two routers are on the network configured for proxy ARP. In this scenario there is the possibility that either one will answer the local server's ARP request for the MAC address of the remote server. If one of the routers has an incorrect routing table entry for the remote network, then there is the risk that traffic to the remote server will occasionally get lost. In other words you can lose routing control.

Note: It is for this and other reasons that it is generally not a good idea to configure proxy ARP on a router. It is also good to always configure a default gateway on your server and use separate routing entries via other routers for all networks your default gateway may not know about.

Some types of bridging mode firewalls need to have proxy ARP enabled to operate properly. These devices are typically inserted as part of a daisy chain connecting multiple network switches together on the same LAN while protecting one section of a LAN from traffic originating on another section. The firewall typically isn't configured with an IP address on the LAN and appears to be an intelligent cable capable of selectively blocking packets.

If you need to enable proxy ARP on a Linux server the /proc filesystem comes into play again. Proxy ARP is handled by files in the /proc/sys/net/ipv4/conf/ directory. This directory then has subdirectories corresponding to each functioning NIC card on your server. Each subdirectory then has a file called proxy_arp. If the value within this file is 0, then proxy ARP on the interface is disabled; if the value is 1 then it is enabled.

You can use the /etc/sysctl.conf file mentioned in Appendix II to activate or disable proxy ARP. The next example activates proxy ARP, first for all interfaces and then for interfaces eth0 and wlan0.

#
# File: /etc/sysctl.conf
#

# Enables Proxy ARP on all interfaces
net/ipv4/conf/all/proxy_arp = 1

# Enables Proxy ARP on interfaces eth1 and wlan0
net/ipv4/conf/eth1/proxy_arp = 1
net/ipv4/conf/wlan0/proxy_arp = 1

You can then activate these settings with the sysctl command.

[root@bigboy tmp] sysctl -p

Configuring Your /etc/hosts File

The /etc/hosts file is just a list of IP addresses and their corresponding server names. Your server will typically check this file before referencing DNS. If the name is found with a corresponding IP address then DNS won't be queried at all. Unfortunately, if the IP address for that host changes, you also have to also update the file. This may not be much of a concern for a single server, but can become laborious if it has to be done companywide. For ease of management, it is often easiest to limit entries in this file to just the loopback interface and also the server's own hostname, and use a centralized DNS server to handle most of the rest. Sometimes you might not be the one managing the DNS server, and in such cases it may be easier to add a quick /etc/hosts file entry till the centralized change can be made.

192.168.1.101 smallfry

In the example above server smallfry has an IP address of 192.168.1.101. You can access 192.168.1.101 using the ping, telnet or any other network aware program by referring to it as smallfry. Here is an example using the ping command to see whether smallfry is alive and well on the network:

[root@bigboy tmp]# ping smallfry
PING zero (192.168.1.101) 56(84) bytes of data.
64 bytes from smallfry (192.168.1.101): icmp_seq=0 ttl=64 time=0.197 ms
64 bytes from smallfry (192.168.1.101): icmp_seq=1 ttl=64 time=0.047 ms

--- smallfry ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 2017ms
rtt min/avg/max/mdev = 0.034/0.092/0.197/0.074 ms, pipe 2
[root@bigboy tmp]#

You can also add aliases to the end of the line which enable you to refer to the server using other names. Here we have set it up so that smallfry can also be accessed using the names tiny and littleguy.

192.168.1.101 smallfry tiny littleguy

You should never have an IP address more than once in this file because Linux will use only the values in the first entry it finds.

192.168.1.101 smallfry # (Wrong)
192.168.1.101 tiny # (Wrong)
192.168.1.101 littleguy # (Wrong)

The loopback Interface's localhost Entry

Usually the first entry in /etc/hosts defines the IP address of the server's virtual loopback interface. This is usually mapped to the name localhost.localdomain (the universal name used when a server refers to itself) and localhost (the shortened alias name). By default, Fedora inserts the hostname of the server between the 127.0.0.1 and the localhost entries like this:

127.0.0.1 bigboy localhost.localdomain localhost

When the server is connected to the Internet this first entry after the 127.0.0.1 needs to be the fully qualified domain name (FQDN) of the server. For example, bigboy.mysite.com, like this:

127.0.0.1 bigboy.my-site.com localhost.localdomain localhost

Some programs such as Sendmail are very sensitive to this and if they detect what they feel is an incorrect FQDN they will default to using the name localhost.localdomain when communicating with another server on the network. This can cause confusion, as the other server also feels it is localhost.localdomain.

Note: You must always have a localhost and localhost.localdomain entry mapping to 127.0.0.1 for Linux to work properly and securely.
Debian / Ubuntu Network Configuration

Many of the core Fedora / Redhat commands and configuration files covered in this chapter can be used in Debian based operating systems, but there are some key differences.
The /etc/network/interfaces File

The main network configuration file is the /etc/network/interfaces file in which all the network interface parameters are defined. The file is divided into stanzas:
The auto Stanza

The auto stanza defines the interfaces that should be automatically initialized when the system boots up.
The mapping Stanza

This stanza maps configuration parameters for an interface depending on the output of a script. For example, on booting the script could prompt you as to whether your laptop Linux system is at home or work with the mapping statement using the answer to configure the appropriate IP address.

By default the much simpler hotplug system is used which assumes that the interfaces will have only one purpose. Typical hotplug configurations simply assign each physical interface with a matching logical interface name (nick name).

mapping hotplug
script grep
map eth0 eth0
map eth1

In this case interface eth0 is specifically given the logical name eth0, while the logical name for eth1 is implied to be the same.
The iface Stanza

The iface stanza defines the characteristics of a logical interface. Typically the first line of these stanzas starts with the word iface, followed by the logical name of the interface, the protocol used, and finally the type of addressing scheme to be used, such as DHCP or static. Protocol keywords include inet for regular TCP/IP, inet6 for IPv6, ipx for the older IPX protocol used by Novell, and loopback for loopback addresses.

Subsequent lines in the stanza define protocol characteristics such as addresses, subnet masks, and default gateways. In this example, interface eth1 is given the IP address 216.10.119.240/27 while interface eth0 gets its IP address using DHCP.

# The primary network interface
auto eth1
iface eth1 inet static
address 216.10.119.240
netmask 255.255.255.224
network 216.10.119.224
broadcast 216.10.119.255
gateway 216.10.119.241
dns-nameservers 216.10.119.241

# The secondary network interface
auto eth0
iface eth0 inet dhcp

Note: When static IP addresses are used, a default gateway usually needs to be defined. Remember to place the gateway statement in the correct stanza with the appropriate router IP address.
Creating Interface Aliases

IP aliases can be easily created in the /etc/network/interfaces file once the main interface has already been defined. A modified duplicate of the main interfaces' iface stanza is required. A colon followed by the sub interface number needs to be added to the first line, and only the subnet mask and the new IP address needs to follow as can be seen in this example for interface eth1:1 with the IP address 216.10.119.239.

auto eth1:1
iface eth1:1 inet static
address 216.10.119.239
netmask 255.255.255.224

Adding Permanent Static Routes

The up option in the appropriate iface stanza of the /etc/network/interfaces file allows you to selectively run commands once the specified interface becomes activated with the ifup command. This makes it useful when adding permanent static routes.

In this example, a route to the 10.0.0.0/8 network via router address 216.10.119.225 has been added. Remember, the up option and the command must reside on the same line of the stanza.

# The primary network interface
auto eth1
iface eth1 inet static
...
...
...
up route add -net 10.0.0.0 netmask 255.0.0.0 gw 216.10.119.225 eth1

A complete /etc/network/interfaces file

We can now construct a complete file based on the previous examples we discussed. Just like in Fedora, interfaces can be activated with the ifup and ifdown commands.

#
# Debian / Ubuntu
#

#
# File: /etc/network/interfaces
#

# The loopback network interface
auto lo
iface lo inet loopback

# This is a list of hotpluggable network interfaces.
# They will be activated automatically by the hotplug subsystem.
mapping hotplug
script grep
map eth0 eth0
map eth1 eth1

# The primary network interface
auto eth1
iface eth1 inet static
address 216.10.119.240
netmask 255.255.255.224
network 216.10.119.224
broadcast 216.10.119.255
gateway 216.10.119.241
# dns-* options are implemented by the resolvconf package, if installed
dns-nameservers 216.10.119.241
wireless-key 98d126d5ac
wireless-essid schaaffe

up route add -net 10.0.0.0 netmask 255.0.0.0 gw 216.10.119.225 eth1

auto eth1:1
iface eth1:1 inet static
address 216.10.119.239
netmask 255.255.255.224

# The secondary network interface
auto eth0
iface eth0 inet dhcp

For more information on the /etc/network/interfaces file just issue the command man interfaces from the command line.

source : www.linuxnetworking.com

Detection Device Uses Laser Light fiber optic Technique

2009-01-13T03:44:00.000-08:00

A compact fiber-optic probe developed for the space program has now proven valuable for patients in the clinic as the first non-invasive early detection device for cataracts, the leading cause of vision loss worldwide.

Researchers from the National Eye Institute (NEI), part of the National Institutes of Health, and the National Aeronautics and Space Administration (NASA) collaborated to develop a simple, safe eye test for measuring a protein related to cataract formation. If subtle protein changes can be detected before a cataract develops, people may be able to reduce their cataract risk by making simple lifestyle changes, such as decreasing sun exposure, quitting smoking, stopping certain medications and controlling diabetes.

"By the time the eye's lens appears cloudy from a cataract, it is too late to reverse or medically treat this process," said Manuel B. Datiles III, M.D., NEI medical officer and lead author of the clinical study. "This technology can detect the earliest damage to lens proteins, triggering an early warning for cataract formation and blindness."

The new device is based on a laser light technique called dynamic light scattering (DLS). It was initially developed to analyze the growth of protein crystals in a zero-gravity space environment. NASA's Rafat R. Ansari, Ph.D., senior scientist at the John H. Glenn Research Center and co-author of the study, brought the technology's possible clinical applications to the attention of NEI vision researchers when he learned that his father's cataracts were caused by changes in lens proteins.

Several proteins are involved in cataract formation, but one known as alpha-crystallin serves as the eye's own anti-cataract molecule. Alpha-crystallin binds to other proteins when they become damaged, thus preventing them from bunching together to form a cataract. However, humans are born with a fixed amount of alpha-crystallin, so if the supply becomes depleted due to radiation exposure, smoking, diabetes or other causes, a cataract can result.

"We have shown that this non-invasive technology that was developed for the space program can now be used to look at the early signs of protein damage due to oxidative stress, a key process involved in many medical conditions, including age-related cataract and diabetes, as well as neurodegenerative diseases such as Alzheimer's and Parkinson's," said NASA's Dr. Ansari. "By understanding the role of protein changes in cataract formation, we can use the lens not just to look at eye disease, but also as a window into the whole body."

The recent NEI-NASA clinical trial, reported in the December 2008 Archives of Ophthalmology, looked at 380 eyes of people aged 7 to 86 who had lenses ranging from clear to severe cloudiness from cataract. Researchers used the DLS device to shine a low-power laser light through the lenses. They had previously determined alpha-crystallin's light-scattering ability, which was then used to detect and measure the amount of alpha-crystallin in the lenses.

They found that as cloudiness increased, alpha-crystallin in the lenses decreased. Alpha-crystallin amounts also decreased as the participants' ages increased, even when the lenses were still transparent. These age-related, pre-cataract changes would remain undetected by currently available imaging tools.

"This research is a prime example of two government agencies sharing scientific information for the benefit of the American people," said NEI director Paul A. Sieving, M.D., Ph.D. "At an individual level, this device could be used to study the effectiveness of anti-cataract therapies or the tendency of certain medications to cause cataract formation."

The DLS technique will now assist vision scientists in looking at long-term lens changes due to aging, smoking, diabetes, LASIK surgery, eye drops for treating glaucoma, and surgical removal of the vitreous gel within the eye, a procedure known to cause cataracts within six months to one year. It may also help in the early diagnosis of Alzheimer's disease, in which an abnormal protein may be found in the lens. In addition, NASA researchers will continue to use the device to look at the impact of long-term space travel on the visual system.

"During a three year mission to Mars, astronauts will experience increased exposure to space radiation that can cause cataracts and other problems," Dr. Ansari explained. "In the absence of proper countermeasures, this may pose a risk for NASA. This technology could help us understand the mechanism for cataract formation so we can work to develop effective countermeasures to mitigate the risk and prevent it in astronauts."

SOURCE: The National Eye Institute (NEI)

Introduction to Networking

2009-01-12T14:05:00.000-08:00

Installing the Linux operating system is only the first step toward creating a fully functional departmental server or Web site. Almost all computers are now networked in some way to other devices therefore a basic understanding of networking and issues related to the topic will be essential to feeling comfortable with Linux servers.

Some groups of IP addresses are reserved for use only in private networks and are not routed over the Internet. These are called private IP addresses and have the following ranges:

This introductory chapter forms the foundation on which the following network configuration and troubleshooting chapters will be built. These chapters will then introduce the remaining chapters that cover Linux troubleshooting, general software installation and the configuration of many of the most popular Linux applications used in corporate departments and Small Office/Home Office (SOHO) environments.

Familiarity with the concepts explained in the following sections will help answer many of the daily questions often posed by coworkers, friends, and even yourself. It will help make the road to Linux mastery less perilous, a road that begins with an understanding of the OSI networking model and TCP/IP.

The OSI Networking Model

The Open System Interconnection (OSI) model, developed by the International Organization for Standardization, defines how the various hardware and software components involved in data communication should interact with each other.

A good analogy would be a traveler who prepares herself to return home through many dangerous kingdoms by obtaining permits to enter each country at the very beginning of the trip. At each frontier our friend has to hand over a permit to enter the country. Once inside, she asks the border guards for directions to reach the next frontier and displays the permit for that new kingdom as proof that she has a legitimate reason for wanting to go there.

In the OSI model each component along the data communications path is assigned a layer of responsibility, in other words, a kingdom over which it rules. Each layer extracts the permit, or header information, it needs from the data and uses this information to correctly forward what's left to the next layer. This layer also strips away its permit and forwards the data to the next layer, and so the cycle continues for seven layers.

The very first layer of the OSI model describes the transmission attributes of the cabling or wireless frequencies used at each "link" or step along the way. Layer 2 describes the error correction methodologies to be used on the link; layer 3 ensures that the data can hop from link to link on the way to the final destination described in its header. When the data finally arrives, the layer 4 header is used to determine which locally installed software application should receive it. The application uses the guidelines of layer 5 to keep track of the various communications sessions it has with remote computers and uses layer 6 to verify that the communication or file format is correct. Finally, layer 7 defines what the end user will see in the form of an interface, be it graphical on a screen or otherwise. A description of the functions of each layer in the model can be seen in Table 2-1.

Table 2-1: The Seven OSI Layers

Layer	Name	Description	Application
7	Application	The user interface to the application	telnet FTP sendmail
6	Presentation	Converts data from one presentation format to another. For example, e-mail text entered into Outlook Express being converted into SMTP mail formatted data.
5	Session	Manages continuing requests and responses between the applications at both ends over the various established connections.
4	Transport	Manages the establishment and tearing down of a connection. Ensures that unacknowledged data is retransmitted. Correctly re-sequences data packets that arrive in the wrong order. After the packet's overhead bytes have been stripped away, the resulting data is said to be a segment.	TCP UDP
3	Network	Handles the routing of data between links that are not physically connected together. After the link's overhead bytes have been stripped away, the resulting data is said to be a packet.	IP ARP
2	Link	Error control and timing of bits speeding down the wire between two directly connected devices. Data sent on a link is said to be structured in frames.	Ethernet ARP
1	Physical	Defines the electrical and physical characteristics of the network cabling and interfacing hardware	Ethernet

An Introduction to TCP/IP

TCP/IP is a universal standard suite of protocols used to provide connectivity between networked devices. It is part of the larger OSI model upon which most data communications is based.

One component of TCP/IP is the Internet Protocol (IP) which is responsible for ensuring that data is transferred between two addresses without being corrupted.

For manageability, the data is usually split into multiple pieces or packets each with its own error detection bytes in the control section or header of the packet. The remote computer then receives the packets and reassembles the data and checks for errors. It then passes the data to the program that expects to receive it.

How does the computer know what program needs the data? Each IP packet also contains a piece of information in its header called the type field. This informs the computer receiving the data about the type of layer 4 transportation mechanism being used.

The two most popular transportation mechanisms used on the Internet are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

When the type of transport protocol has been determined, the TCP/UDP header is then inspected for the "port" value, which is used to determine which network application on the computer should process the data. This is explained in more detail later.

TCP Is a Connection-Oriented Protocol

TCP opens up a virtual connection between the client and server programs running on separate computers so that multiple and/or sporadic streams of data can be sent over an indefinite period of time between them. TCP keeps track of the packets sent by giving each one a sequence number with the remote server sending back acknowledgment packets confirming correct delivery. Programs that use TCP therefore have a means of detecting connection failures and requesting the retransmission of missing packets. TCP is a good example of a connection-oriented protocol.

How TCP Establishes A Connection

Any form of communication requires some form of acknowledgement for it to become meaningful. Someone knocks on the door to a house, the person inside asks "Who is it?", to which the visitor replies, "It's me!" Then the door opens. Both persons knew who was on the other side of the door before it opened and now a conversation can now begin.

TCP acts in a similar way. The server initiating the connection sends a segment with the SYN bit set in TCP header. The target replies with a segment with the SYN and ACK bits set, to which the originating server replies with a segment with the ACK bit set. This SYN, SYN-ACK, ACK mechanism is often called the "three-way handshake".

The communication then continues with a series of segment exchanges, each with the ACK bit set. When one of the servers needs to end the communication, it sends a segment to the other with the FIN and ACK bits set, to which the other server also replies with a FIN-ACK segment also. The communication terminates with a final ACK from the server that wanted to end the session.

This is the equivalent of ending a conversation by saying "I really have to go now, I have to go for lunch", to which the reply is "I think I'm finished here too, see you tomorrow..." The conversation ends with a final "bye" from the hungry person.

Here is a modified packet trace obtained from the tethereal program discussed in Chapter 4, "Simple Network Troubleshooting". You can clearly see the three way handshake to connect and disconnect the session.

hostA -> hostB TCP 1443 > http [SYN] Seq=9766 Ack=0 Win=5840 Len=0
hostB -> hostA TCP http > 1443 [SYN, ACK] Seq=8404 Ack=9767 Win=5792 Len=0
hostA -> hostB TCP 1443 > http [ACK] Seq=9767 Ack=8405 Win=5840 Len=0
hostA -> hostB HTTP HEAD/HTTP/1.1
hostB -> hostA TCP http > 1443 [ACK] Seq=8405 Ack=9985 Win=54 Len=0
hostB -> hostA HTTP HTTP/1.1 200 OK
hostA -> hostB TCP 1443 > http [ACK] Seq=9985 Ack=8672 Win=6432 Len=0
hostB -> hostA TCP http > 1443 [FIN, ACK] Seq=8672 Ack=9985 Win=54 Len=0
hostA -> hostB TCP 1443 > http [FIN, ACK] Seq=9985 Ack=8673 Win=6432 Len=0
hostB -> hostA TCP http > 1443 [ACK] Seq=8673 Ack=9986 Win=54

In this trace, the sequence number represents the serial number of the first byte of data in the segment. So in the first line, a random value of 9766 was assigned to the first byte and all subsequent bytes for the connection from this host will be sequentially tracked. This makes the second byte in the segment number 9767, the third number 9768 etc. The acknowledgment number or Ack, not to be confused with the ACK bit, is the byte serial number of the next segment it expects to receive from the other end, and the total number of bytes cannot exceed the Win or window value that follows it. If data isn't received correctly, the receiver will re-send the requesting segment asking for the information to be sent again. The TCP code keeps track of all this along with the source and destination ports and IP addresses to ensure that each unique connection is serviced correctly.

UDP, TCP's "Connectionless" Cousin

UDP is a connectionless protocol. Data is sent on a "best effort" basis with the machine that sends the data having no means of verifying whether the data was correctly received by the remote machine. UDP is usually used for applications in which the data sent is not mission-critical. It is also used when data needs to be broadcast to all available servers on a locally attached network where the creation of dozens of TCP connections for a short burst of data is considered resource-hungry.

TCP and UDP Ports

The data portion of the IP packet contains a TCP or UDP segment sandwiched inside. Only the TCP segment header contains sequence information, but both the UDP and the TCP segment headers track the port being used. The source/destination port and the source/destination IP addresses of the client & server computers are then combined to uniquely identify each data flow.

Certain programs are assigned specific ports that are internationally recognized. For example, port 80 is reserved for HTTP Web traffic, and port 25 is reserved for SMTP e-mail. Ports below 1024 are reserved for privileged system functions, and those above 1024 are generally reserved for non-system third-party applications.

Usually when a connection is made from a client computer requesting data to the server that contains the data:

The client selects a random previously unused "source" port greater than 1024 and queries the server on the "destination" port specific to the application. If it is an HTTP request, the client will use a source port of, say, 2049 and query the server on port 80 (HTTP)

The server recognizes the port 80 request as an HTTP request and passes on the data to be handled by the Web server software. When the Web server software replies to the client, it tells the TCP application to respond back to port 2049 of the client using a source port of port 80.

The client keeps track of all its requests to the server's IP address and will recognize that the reply on port 2049 isn't a request initiation for "NFS", but a response to the initial port 80 HTTP query.

The TCP/IP "Time To Live" Feature

Each IP packet has a Time to Live (TTL) section that keeps track of the number of network devices the packet has passed through to reach its destination. The server sending the packet sets the initial TTL value, and each network device that the packet passes through then reduces this value by 1. If the TTL value reaches 0, the network device will discard the packet.

This mechanism helps to ensure that bad routing on the Internet won't cause packets to aimlessly loop around the network without being removed. TTLs therefore help to reduce the clogging of data circuits with unnecessary traffic.

Remember this concept as it will be helpful in understanding the traceroute troubleshooting technique outlined in Simple Network Troubleshooting, that covers Network Troubleshooting.

The ICMP Protocol and Its Relationship to TCP/IP

There is another commonly used protocol called the Internet Control Message Protocol (ICMP). It is not strictly a TCP/IP protocol, but TCP/IP-based applications use it frequently.

ICMP provides a suite of error, control, and informational messages for use by the operating system. For example, IP packets will occasionally arrive at a server with corrupted data due to any number of reasons including a bad connection; electrical interference, or even misconfiguration. The server will usually detect this by examining the packet and correlating the contents to what it finds in the IP header's error control section. It will then issue an ICMP reject message to the original sending machine saying that the data should be re-sent because the original transmission was corrupted.

ICMP also includes echo and echo reply messages used by the Linux ping command to confirm network connectivity. ICMP TTL expired messages are also sent by network devices back to the originating server whenever the TTL in a packet is decremented to zero. More information on ICMP messages can be found in both Appendix 1, Miscellaneous Linux Topics, and Simple Network Troubleshooting, on network troubleshooting.

How IP Addresses Are Used To Access Network Devices

All TCP/IP enabled devices connected to the Internet have an Internet Protocol (IP) address. Just like a telephone number, it helps to uniquely identify a user of the system. The Internet Assigned Numbers Authority (IANA) is the organization responsible for assigning IP addresses to Internet Service Providers (ISPs) and deciding which ones should be used for the public Internet and which ones should be used on private networks.

IP addresses are in reality a string of 32 binary digits or bits. For ease of use, network engineers often divide these 32 bits into four sets of 8 bits (or octets), each representing a number from 0 to 255. Each number is then separated by a period (.) to create the familiar dotted decimal notation. An example of an IP address that follows these rules is 97.65.25.12.

Private IP Addresses

10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

Home networking equipment/devices usually are configured in the factory with an IP address in the range 192.168.1.1 to 192.168.1.255.

You may be wondering how devices using private addresses could ever access the Internet if the use of private addresses on the Internet is illegal. The situation gets even more confusing if you consider the fact that hundreds of thousands of office and home networks use these same addresses. This must cause networking confusion. Don't worry, this problem is overcome by NAT.

The localhost IP Address

Whether or not your computer has a network interface card it will have a built-in IP address with which network-aware applications can communicate with one another. This IP address is defined as 127.0.0.1 and is frequently referred to as localhost. This concept is important to understand, and will be revisited in many later chapters.

Network Address Translation (NAT) Makes Private IPs Public

Your router/firewall will frequently be configured to give the impression to other devices on the Internet that all the servers on your home/office network have a valid public IP address, and not a "private" IP address. This is called network address translation (NAT) and is often also called IP masquerading in the Linux world. There are many good reasons for this, the two most commonly stated are:

No one on the Internet knows your true IP address. NAT protects your home PCs by assigning them IP addresses from "private" IP address space that cannot be routed over the Internet. This prevents hackers from directly attacking your home systems because packets sent to the "private" IP will never pass over the Internet.

Hundreds of PCs and servers behind a NAT device can masquerade as a single public IP address. This greatly increases the number of devices that can access the Internet without running out of "public" IP addresses.

You can configure NAT to be one to one in which you request your ISP to assign you a number of public IP addresses to be used by the Internet-facing interface of your firewall and then you pair each of these addresses to a corresponding server on your protected private IP network. You can also use many to one NAT, in which the firewall maps a single IP address to multiple servers on the network.

As a general rule, you won't be able to access the public NAT IP addresses from servers on your home network. Basic NAT testing requires you to ask a friend to try to connect to your home network from the Internet.

Port Forwarding with NAT Facilitates Home-Based Web sites

In a simple home network, all servers accessing the Internet will appear to have the single public IP address of the router/firewall because of many to one NAT. Because the router/firewall is located at the border crossing to the Internet, it can easily keep track of all the various outbound connections to the Internet by monitoring:

The IP addresses and TCP ports used by each home based server and mapping it to

The TCP ports and IP addresses of the Internet servers with which they want to communicate.

This arrangement works well with a single NAT IP trying to initiate connections to many Internet addresses. The reverse isn't true.

New connections initiated from the Internet to the public IP address of the router/firewall face a problem. The router/firewall has no way of telling which of the many home PCs behind it should receive the relayed data because the mapping mentioned earlier doesn't exist beforehand. In this case the data is usually discarded.

Port forwarding is a method of counteracting this. For example, you can configure your router/firewall to forward TCP port 80 (Web/HTTP) traffic destined to the outside NAT IP to be automatically relayed to a specific server on the inside home network

As you may have guessed, port forwarding is one of the most common methods used to host Web sites at home with DHCP DSL.

DHCP

The Dynamic Host Configuration Protocol (DHCP) is a protocol that automates the assignment of IP addresses, subnet masks default routers, and other IP parameters.

The assignment usually occurs when the DHCP configured machine boots up, or regains connectivity to the network. The DHCP client sends out a query requesting a response from a DHCP server on the locally attached network. The DHCP server then replies to the client PC with its assigned IP address, subnet mask, DNS server and default gateway information.

The assignment of the IP address usually expires after a predetermined period of time, at which point the DHCP client and server renegotiate a new IP address from the server's predefined pool of addresses. Configuring firewall rules to accommodate access from machines who receive their IP addresses via DHCP is therefore more difficult because the remote IP address will vary from time to time. You'll probably have to allow access for the entire remote DHCP subnet for a particular TCP/UDP port.

Most home router/firewalls are configured in the factory to be DHCP servers for your home network. You can also make your Linux box into a DHCP server, once it has a fixed IP address.

The most commonly used form of DSL will also assign the outside interface of your router/firewall with a single DHCP provided IP address.

How DNS Links Your IP Address To Your Web Domain

The domain name system (DNS) is a worldwide server network used to help translate easy to remember domain names like www.linuxhomenetworking.com into an IP address that can be used behind the scenes by your computer. Here step by step description of what happens with a DNS lookup.

Most home computers will get the IP address of their DNS server via DHCP from their router/firewall.
Home router/firewall providing DHCP services often provides its own IP address as the DNS name server address for home computers.
The router/firewall then redirects the DNS queries from your computer to the DNS name server of your Internet service provider (ISP).
Your ISP's DNS server then probably redirects your query to one of the 13 "root" name servers.
The root server then redirects your query to one of the Internet's ".com" DNS name servers which will then redirect the query to the "linuxhomenetworking.com" domain's name server.
The linuxhomenetworking.com domain name server then responds with the IP address for www.linuxhomenetworking.com

As you can imagine, this process can cause a noticeable delay when you are browsing the Web. Each server in the chain will store the most frequent DNS name to IP address lookups in a memory cache which helps to speed up the response. Configuring DNS, explains how to you can make your Linux box into a caching or regular DNS server for your network or Web site if your ISP provides you with fixed IP addresses. Chapter 19, Dynamic DNS, explains how to configure DNS for a Web site housed on a DHCP DSL circuit where the IP address constantly changes. It explains the auxiliary DNS standard called dynamic DNS (DDNS) that was created for this type of scenario.

IP Version 6 (IPv6)

Most Internet-capable networking devices use version 4 of the Internet Protocol (IPv4) which I have described here. You should also be aware that there is now a version 6 (IPv6) that has recently been developed as a replacement.

With only 32 bits, the allocation of version 4 addresses will soon be exhausted between all the world's ISPs. Version 6, which uses a much larger 128-bit address offers eighty billion, billion, billion times more IP addresses which it is hoped should last for most of the 21st century.

IPv6 packets are also labeled to provide quality-of-service information that can be used in prioritizing real-time applications, such as video and voice, over less time-sensitive ones such as regular Web surfing and chat. IPv6 also inherently supports the IPSec protocol suite used in many forms of secured networks, such as virtual private networks (VPNs).

Most current operating systems support IPv6 even though it isn't currently being used extensively within corporate or home environments. Expect it to become an increasingly bigger part of your network planning in years to come.

How Subnet Masks Group IP Addresses into Networks

Subnet masks are used to tell which part of the IP address represents the network on which the computer is connected (network portion) and the computer's unique identifier on that network (host portion). The term netmasks is often used interchangeably with the term subnet masks, this book will use the latter term for the sake of consistency.

A simple analogy would be a phone number, such as (808) 225-2468. The (808) represents the area code, and the 225-2468 represents the telephone within that area code. Subnet masks allow you to specify how long you want the area code to be (network portion) at the expense of the number of telephones in that are in the area code (host portion)

Most home networks use a subnet mask of 255.255.255.0. Each 255 means this octet is for the area code (network portion). So if your server has an IP address of 192.168.1.25 and a subnet mask of 255.255.255.0, the network portion would be 192.168.1 and the server or host would be device #25 on that network.

In all cases, the first IP address in a network is reserved as the network's base address and the last one is reserved for broadcast traffic that is intended to be received by all devices on the network. In our example, 192.168.1.0 would be the network address and 192.168.1.255 would be used for broadcasts. This means you can then use IP addresses from #1 to #254 on your private network.

Calculating The Number of Addresses Assigned to a Subnet

Most office and home networks use networks with 255 IP addresses or less in which the subnet mask starts with the numbers 255.255.255. This is not a pure networking text, so I'll not discuss larger networks because that can become complicated, but in cases where less than 255 IP addresses are required a few apply. There are only seven possible values for the last octet of a subnet mask. These are 0, 192, 128, 224, 240, 248 and 252. You can calculate the number of IP addresses for each of these by subtracting the value from 256.

In many cases the subnet mask isn't referred to by the dotted decimal notation, but rather by the actual number of bits in the mask. So for example a mask of 255.255.255.0 may be called a /24 (slash 24) mask instead. A list of the most commonly used masks in the office or home environment is presented in Table 2-2.

Table 2-2: The "Dotted Decimal" And "Slash" Subnet Mask Notations

Dotted Decimal Format	Slash Format	Available Addresses
255.255.255.0	/24	256
255.255.255.128	/25	128
255.255.255.192	/26	64
255.255.255.224	/27	32
255.255.255.240	/28	16
255.255.255.248	/29	8
255.255.255.252	/30	4

So for example, if you have a subnet mask of 255.255.255.192, then you have 64 IP addresses in your subnet (256 - 192)

Calculating the Range of Addresses on Your Network

If someone gives you an IP address of 97.158.253.28 and a subnet mask of 255.255.255.248, how do you determine the network address and the broadcast address, in other words the boundaries, of your network? The following section outlines the steps to do this using both a manual and programmed methodology.

Manual Calculation

Take out your pencil and paper, manual calculation can be tricky. Here we go!

Subtract the last octet of the subnet mask from 256 to give the number of IP addresses in the subnet. (256 - 248) = 8
Divide the last octet of the IP address by the result of step 1; don't bother with the remainder (for example 28 / 8 = 3). This gives you the theoretical number of subnets of the same size that are below this IP address.
Multiply this result by the result of step 1 to get the network address (8 x 3 = 24). Think of it as the third subnet with 8 addresses in it. The network address is therefore 97.158.253.24
The broadcast address is the result of step 3 plus the result of step 1 minus 1. (24 + 8 -1 = 31). Think of it as the broadcast address being the network address plus the number of IP addresses in the subnet minus 1". The broadcast address is 97.158.253.31

Let's do this for 192.168.3.56 with a mask of 255.255.255.224:

256 - 224 = 32
56/32 = 1
32 x 1 = 32. Therefore the network base address is 192.168.3.32
32 + 32 - 1 = 63. Therefore the broadcast address is 192.168.3.63

Let's do this for 10.0.0.75 with a mask of 255.255.255.240

256 - 240 = 16
75/16 = 4
16 x 4 = 64. Therefore the network base address is 10.0.0.64
64 + 16 -1 = 79. Therefore the broadcast address is 10.0.0.79

Note: As a rule of thumb, the last octet of your network base address must be divisible by the "256 minus the last octet of your subnet mask" and leave no remainder. If you are sub-netting a large chunk of IP addresses it's always a good idea to lay it out on a spreadsheet to make sure there are no overlapping subnets. Once again, this calculation exercise only works with subnet masks that start with "255.255.255".

Calculation Using a Script

There is a BASH script in Appendix II, Codes, Script, and Configuration, that will do this for you. Here is an example of how to use it, just provide the IP address followed by the subnet mask as arguments. It will accept subnet masks in dotted decimal format or /value format

[root@bigboy tmp]# ./subnet-calc.sh 216.151.193.92 /28
IP Address           : 216.151.193.92
Network Base Address : 216.151.193.80
Broadcast Address    : 216.151.193.95
Subnet Mask          : 255.255.255.240
Subnet Size          : 16 IP Addresses
[root@bigboy tmp]#

Subnet Masks for the Typical Business DSL Line

If you purchased a DSL service from your ISP that gives you fixed IP addresses, they will most likely provide you with a subnet mask of 255.255.255.248 that defines 8 IP addresses. For example, if the ISP provides you with a public network address of 97.158.253.24, a subnet mask of 255.255.255.248, and a gateway of 97.158.253.25, then your IP addresses will be:

97.158.253.24 - Network base address
97.158.253.25 - Gateway
97.158.253.26 - Available
97.158.253.27 - Available
97.158.253.28 - Available
97.158.253.29 - Available
97.158.253.30 - Available
97.158.253.31 - Broadcast

The Physical and Link Layers

TCP/IP can be quite interesting, but a knowledge of the first two layers of the OSI model are important too, because without them, even the most basic communication would be impossible.

There are very many standards that define the physical, electrical, and error-control methodologies of data communication. One of the most popular ones in departmental networks is Ethernet, which is available in a variety of cable types and speed capabilities, but the data transmission and error correction strategy is the same in all.

Ethernet used to operate primarily in a mode where every computer on a network section shared the same Ethernet cable. Computers would wait until the line was clear before transmitting. They would then send their data while comparing what they wanted to send with what they actually sent on the cable as a means of error detection. If a mathematical comparison, or cyclic redundancy check (CRC), detected any differences between the two, the server would assume that it transmitted data simultaneously with another server on the cable. It would then wait some random time and retransmit at some later stage when the line was clear again.

Transmitting data only after first sensing whether the cable, which was strung between multiple devices, had the correct signaling levels is a methodology called carrier sense, multiple access or CSMA. The ability to detect garbling due to simultaneous data transmissions, also known as collisions, is called collision detect or CD. You will frequently see references to Ethernet being a CSMA/CD technology for this reason and similar schemes are now being used in wireless networks.

Ethernet devices are now usually connected via a dedicated cable, using more powerful hardware capable of simultaneously transmitting and receiving without interference, thereby making it more reliable and inherently faster than its predecessor versions. The original Ethernet standard has a speed of 10 Mbps; the most recent versions can handle up to 40Gbps!

The 802.11 specifications that define many wireless networking technologies are another example of commonly used layer 1 and 2 components of the OSI model. DSL, cable modem standards and, T1 circuits are all parts of these layers.

The next few sections describe many physical and link layer concepts and the operation of the devices that use them to connect the computers in our offices and homes.

Networking Equipment Terminology

Up to this point you have had only an introduction to the theory of the first two OSI layers. Now we'll cover the hardware used to implement them.

Network Interface Cards

Your network interface card is also frequently called a NIC. Currently, the most common types of NIC used in the home and office are Ethernet and wireless Ethernet cards.

The Meaning of the NIC Link Light

The link light signifies that the NIC card has successfully detected a device on the other end of the cable. This indicates that you are using the correct type of cable and that the duplex has been negotiated correctly between the devices at both ends.

Duplex Explained

Full duplex data paths have the capability of allowing the simultaneous sending and receiving of data. Half duplex data paths can transmit in both directions too, but in only one direction at a time.

Full duplex uses separate pairs of wires for transmitting and receiving data so that incoming data flows don't interfere with outgoing data flows.

Half duplex uses the same pairs of wires for transmitting and receiving data. Devices that want to transmit information have to wait their turn until the "coast is clear" at which point they send the data. Error-detection and data-retransmission mechanisms ensure that the data reaches the destination correctly and are specifically designed to remedy data corruption caused when multiple devices start transmitting at the same time.

A good analogy for full duplex communications is the telephone, in which both parties can speak at the same time. Half duplex on the other hand is more like a walkie-talkie in which both parties have to wait until the other is finished before they can speak.

Data transfer speeds will be low and error levels will be high if you have a device at one end of a cable set to full duplex and a device at the other end of the cable set to half duplex.

Most modern network cards can autonegotiate duplex with the device on the other end of the wire. It is for this reason that duplex settings aren't usually a problem for Linux servers.

The MAC Address

The media access control (MAC) address can be equated to the serial number of the NIC. Every IP packet is sent out of your NIC wrapped inside an Ethernet frame that uses MAC addresses to direct traffic on your locally attached network.

MAC addresses therefore have significance only on the locally attached network. As the packet hops across the Internet, its source/destination IP address stays the same, but the MAC addresses are reassigned by each router on the way using a process called ARP.

How ARP Maps the MAC Address to Your IP Address

The Address Resolution Protocol (ARP) is used to map MAC addresses to network IP addresses. When a server needs to communicate with another server it does the following steps:

The server first checks its routing table to see which router provides the next hop to the destination network.
If there is a valid router, let's say with an IP address of 192.168.1.1, the server checks its ARP table to see whether it has the MAC address of the router's NIC. You could very loosely view this as the server trying to find the Ethernet serial number of the next hop router on the local network, thereby ensuring that the packet is sent to the correct device.
If there is an ARP entry, the server sends the IP packet to its NIC and tells the NIC to encapsulate the packet in a frame destined for the MAC address of the router.
If there is no ARP entry, the server issues an ARP request asking that router 192.168.1.1 respond with its MAC address so that the delivery can be made. When a reply is received, the packet is sent and the ARP table is subsequently updated with the new MAC address.
As each router in the path receives the packet, it plucks the IP packet out of the Ethernet frame, leaving the MAC information behind. It then inspects the destination IP address in the packet and use its routing table to determine the IP address of the next router on the path to this destination.
The router then uses the "ARP-ing" process to get the MAC address of this next hop router. It then reencapsulates the packet in an Ethernet frame with the new MAC address and sends the frame to the next hop router. This relaying process continues until the packet reaches the target computer.
If the target server is on the same network as the source server, a similar process occurs. The ARP table is queried. If no entry is available, an ARP request is made asking the target server for its MAC address. Once a reply is received, the packet is sent and the ARP table is subsequently updated with the new MAC address.
The server will not send the data to its intended destination unless it has an entry in its ARP table for the next hop. If it doesn't, the application needing to communicate will issue a timeout or time exceeded error.
As can be expected, the ARP table contains only the MAC addresses of devices on the locally connected network. ARP entries are not permanent and will be erased after a fixed period of time depending on the operating system used.

Linux Networking, which covers Linux network topics, shows how to see your ARP table and the MAC addresses of your server's NICs.

Common ARP Problems When Changing A NIC

You may experience connectivity problems if you change the MAC address assigned to an IP address. This can happen if you swap a bad NIC card in a server, or replace a bad server but have the new one retain the IP address of the old.

Routers typically save learned MAC to IP address map entries in a cache and won't refresh them unless a predefined period of time has elapsed. Changing the NIC, while retaining the IP address can cause problems as the router will continue to send frames onto the network with the correct target IP address but the old target MAC address. The server with the new NIC won't respond as the frame's target MAC doesn't match it's own.

This problem can be fixed in one of two ways. You can delete all the ARP entries in the router's cache. The second solution is to log into the server's console and ping it's gateway. The router will detect the MAC to IP address change and it will readjust its ARP table.

The Two Broad Types Of Networking Equipment

There are two main types of networking equipment; Data Communications Equipment (DCE) which is intended to act as the primary communications path, and Data Terminal Equipment (DTE) which acts as the source or destination of the transmitted data.

Data Terminal Equipment

DTE devices were originally computer terminals located at remote offices or departments that were directly connected modems. The terminals would have no computing power and only functioned as a screen/keyboard combination for data processing.

Nowadays most PCs have their COM and Ethernet ports configured as if they were going to be connected to a modem or other type of purely networking-oriented equipment.

Data Communications Equipment

A DCE is also known as Data Circuit-Terminating Equipment and refers to such equipment as modems and other devices designed primarily to provide network access.

Using Straight-Through/Crossover Cables to Connect DTEs And DCEs

When a DCE is connected to a DTE, you will need a straight-through cable. DCEs connected to DCEs or DTEs connected to DTEs require crossover cables. This terminology is generally used with Ethernet cables.

The terminology can be different for cables used to connect serial ports together. When connecting a PC's COM port (DTE) to a modem (DCE) the straight-through cable is frequently called a modem cable. When connecting two PCs (DTE) together via their COM ports, the crossover cable is often referred to as a null modem cable.

Some manufacturers configure the Ethernet ports of their networking equipment to be either of the DTE or the DCE type, and other manufacturers have designed their equipment to flip automatically between the two types until it gets a good link. As you can see, confusion can arise when selecting a cable. If you fail to get a link light when connecting your Ethernet devices together, try using the other type of cable.

A straight-through Ethernet cable is easy to identify. Hold the connectors side by side, pointing in the same direction with the clips facing away from you. The color of the wire in position #1 on connector #1 should be the same as that of position #1 on connector #2. The same would go for positions #2 through #8, that is, the same color for corresponding wires on each end. A crossover cable has them mixed up. Table 2-3 provides some good rules of thumb.

Table 2-3: Cabling Rules of Thumb

Scenario	Likely Cable Type
PC to PC	Crossover
Hub to hub	Crossover
Switch to switch	Crossover
PC to modem	Straight-Through
PC to hub	Straight-Through
PC to switch	Straight-Through

Connectivity Using Hubs

A hub is a device into which you can connect all devices on a network so that they can talk together. Hubs physically cross-connect all their ports with one another which causes all traffic sent from a server to the hub to be blurted out to all other servers connected to that hub whether they are the intended recipient or not.

Hubs have no, or very little, electronics inside and therefore do not regulate traffic. It is possible for multiple servers to speak at once with all of them receiving garbled messages. When this happens the servers try again, after a random time interval, until the message gets through correctly.

It is for these reasons that Ethernet devices that plug into hubs should be set to half duplex.

Note: Hubs can add a lot of delays to your network because of the message garbling collisions and retransmissions. A switch is a much more reliable and predictable alternative, and ones made for the home often cost only a few dollars more.

Using Switches as a Faster Alternative to Hubs

A switch is also a device into which you can connect all devices on a home network so that they can talk together. Unlike a hub, traffic sent from Server A to Server B will be received only by Server B. The only exception is broadcast traffic which is blurted out to all the servers simultaneously.

Switches regulate traffic, thereby eliminating the possibility of message garbling and providing a more efficient traffic flow.

Devices that plug into switches should be set to full duplex to take full advantage of the dedicated bandwidth coming from each switch port.

Local Area Networks

A local area network (LAN) is a grouping of ports on a hub, switch or tied to a wireless access point (WAP) that can communicate only with each other.

It is possible to connect multiple switches and/or hubs in a chain formation to create a LAN with more ports. This is often called daisy chaining.

Switches and hubs provide no access control between servers connected to the same LAN. This is why network administrators group trusted servers having similar roles on the same LAN.

Servers use their IP address and subnet mask and the IP address of the remote server to determine whether they are both on the same network. If not, they attempt to communicate with each other via routers that interconnect their LANs. Routers are also capable of filtering traffic passing between the two LANs therefore providing additional security.

Larger, more expensive switches can be configured to assign only certain ports to prespecified virtual LANs or (VLANs) chosen by the network administrator. In this case, the switch houses ports on multiple LANs. A router still needs to be connected to each VLAN for internetwork communication.

How Routers Interconnect LANs

As stated before, switches and hubs usually have only servers connected to them that have been configured as being part of the same network. By connecting its NIC cards to multiple LANs, a correctly configured router is capable of relaying traffic between networks.

Routers can also be configured to deny communication between specific servers on different networks. They can also filter traffic based on the TCP port section of each packet. For example, it is possible to deny communication between two servers on different networks that intend to communicate on TCP port 80, and allow all other traffic between them. Routers therefore direct and regulate traffic between separate networks, much like a traffic policeman.

If you intend to route between networks, you must reserve an IP address for a router for each network and make sure that the router is directly connected to the LAN associated with that network. The network engineer responsible for the router will also have to specify which locally connected networks can be advertised to the router's neighbors and whether this information can be relayed to all the routers in an administrative zone, or routing domain.

In this example, we can see that the router is aware of many different networks (represented by the slash notation for subnet masks). The routing table also shows the best serial and VLAN type interfaces to use to get to these destinations and the IP address of the neighboring router through which traffic needs to be relayed to get there.

router>show ip route
...
...
...
Gateway of last resort is 10.1.1.1.1 to network 0.0.0.0

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
S       172.16.0.0/16 is directly connected, Null0
S       172.16.6.0/24 is directly connected, Null0
172.17.0.0/24 is subnetted, 2 subnets
S       172.17.2.0 [1/0] via 10.1.1.1.1
S    192.168.200.0/24 is directly connected, Null0
10.0.0.0/8 is variably subnetted, 64 subnets, 8 masks
O E1    10.2.0.0/16 [110/22] via 10.89.0.2, 3w1d, Serial1/0/1
C       10.119.3.0/24 is directly connected, Vlan3
O       10.2.2.0/24 [110/3] via 10.89.0.2, 3w1d, Serial1/0/1
O       10.132.10.0/24 [110/3] via 10.119.2.2, 3w1d, Vlan2
O       10.119.0.20/30 [110/3] via 10.89.0.26, 7w0d, Serial1/0/0
S       10.253.72.0/21 [1/0] via 10.1.1.13
C       10.10.192.0/24 is directly connected, Vlan114
O       10.230.232.0/22 [110/4] via 10.89.0.26, 7w0d, Serial1/0/0
S*   0.0.0.0/0 [1/0] via 10.1.1.1.1
router>

In home networks, routers usually have only two interfaces that provide connectivity to the Internet via network address translation or NAT. In other words routers act as gateways to the wider world and it won't be surprising to learn that routers are frequently referred to as "gateways".

Note: The term gateway specifically refers to a device that routes traffic between dissimilar network protocols (IP to Appletalk) or access methods (Ethernet to DSL). Routers transfer traffic where both the protocols and communications medium are the same. The terms are frequently used interchangeably, especially if only one network protocol is being used. Therefore a home DSL router that provides IP Internet access to an Ethernet network is technically both a gateway and a router. The distinction can be important in complicated networking environments where newer technologies need to talk with older ones using incompatible communications protocols.

How Simple Routing Works

In the broader networking sense, a "route" refers to the path data takes to traverse from its source to its destination. Each router along the way may also be referred to as a hop.

Usually when we speak about a route on a Linux box, we are referring to the IP address of the first hop needed to reach the desired destination network. It is assumed that this first hop will know how to automatically relay the packet.

As explained previously, routers are designed to exchange routing information dynamically, and can therefore intelligently redirect traffic to bypass failed network links. Home Linux boxes frequently don't run a dynamic routing protocol and therefore rely on "static" routes issued by the system administrator at the command line or in configuration files to determine the next hop to all desired networks.

Linux Networking, which covers Linux network topics, shows how to add static routes to your Linux box and also how you can convert it into a simple router.

Default Gateways, The Routers Of Last Resort

A default gateway is the router that is used when no alternative devices can be found to relay the traffic. They are often called "routers of last resort".

Say for example you have two routers R1 and R2. R1 is connected to both your SOHO home network and the Internet. R2 is connected to SOHO home network and is capable of relaying data to other corporate networks with addresses starting with 10.X.X.X via another NIC card.

You could put a route on your SOHO servers that states:

Go to network 10.0.0.0 255.0.0.0 via router R2
Go to everything else via router R1. R1 therefore would be considered your default gateway

For most home networks, your default gateway would be the router/firewall connected to the Internet.

Linux Networking, which covers Linux network topics, shows how to configure the default gateway on your Linux box.

Firewalls Help Provide a Secure Routing Environment

Firewalls can be viewed as routers with more enhanced abilities to restrict traffic, not just by port and IP address as routers do. Specifically, firewalls can detect malicious attempts to subvert the TCP/IP protocol. A short list of capabilities includes:

Throttling traffic to a server when too many unfulfilled connections are made to it
Restricting traffic being sent to obviously bogus IP addresses
Providing network address translation or NAT

Routers are designed to make packets flow as quickly as possible with the minimum amount of inspection. Firewalls are used as close to the source or target of data communication as possible to try to ensure that the data hasn't been subverted.

Firewalls can often create an encrypted data path between two Private networks across the Internet providing secure communication with a greatly reduced chance of eavesdropping. These communication channels are called Virtual Private Networks or VPNs and are frequently used to connect branch offices to the corporate headquarters and also to allow sales representatives to get access to sensitive pricing information when traveling from town to town.

Additional Introductory Topics

The last few topics of this chapter may not appear to be directly related to networking, but they cover Linux help methods that you'll use extensively and the File Transfer Protocol (FTP) package, which enables you to download all the software you need to get your Linux server operational as quickly as possible.

The File Transfer Protocol

FTP is one of the most popular applications used to copy files between computers via a network connection. Knowledge of FTP is especially important and is a primary method of downloading software for Linux systems.

There are a number of commercially available GUI based clients you can load on your PC to do this, such as WSFTP and CuteFTP. You can also use FTP from the command line as shown in Installing RPM Software Installation, on RPM software installation.

From the remote user's perspective, there are two types of FTP. The first is regular FTP which is used primarily to allow specific users to download files to their systems. The remote FTP server prompts you for a specific username and password to gain access to the data.

The second method, anonymous FTP is used primarily to allow any remote user to download files to their systems. The remote FTP server prompts you for a username, at which point the user types anonymous or ftp with the password being any valid e-mail address.

From the systems administrator's perspective, there are another two categories. These are "active" and "passive" FTP which is covered in more detail in Linux FTP server Setup.

It is good to remember that FTP isn't very secure as usernames, passwords and data are sent across the network unencrypted. More secure forms such as SFTP (Secure FTP) and SCP (Secure Copy) are available as a part of the Secure Shell package (covered in Secure Remote Login and File Copying) that is normally installed by default with Fedora.

Linux Help

Linux help files are accessed using the man or manual pages. From the command line you issue the man command followed by the Linux command or file about which you want to get information. If you want to get information on the ssh command, then you'd use the command man ssh.

[root@bigboy tmp]# man ssh

If you want to search all the man pages for a keyword, then use the man command with the -k switch, for example, man -k ssh which will give a list of all the man pages that contain the word ssh.

[root@bigboy tmp]# man -k ssh
...
...
ssh                  (1)  - OpenSSH SSH client (remote login program)
ssh [slogin]         (1)  - OpenSSH SSH client (remote login program)
ssh-agent            (1)  - authentication agent
ssh-keyscan          (1)  - gather ssh public keys
ssh_config           (5)  - OpenSSH SSH client configuration files
sshd                 (8)  - OpenSSH SSH daemon
sshd_config          (5)  - OpenSSH SSH daemon configuration file
...
...
[root@bigboy tmp]#

This book is targeted at proficient Linux beginners and above so I'll be using a wide variety of commands in this book without detailed explanations to help keep the flow brisk. If you need more help on a command, use its man page to get more details on what it does and the syntax it needs. Linux help can sometimes be cryptic, but with a little practice the man pages can become your friend.

source : www.linuxhomenetworking.com

How to Choose an ISP

2009-01-10T14:09:00.000-08:00

Once you've had a taste of the Internet and all it has to offer, you will want to stay connected. To make an online connection you need an Internet Service Provider (ISP). This is the company that provides your hook-up to the Internet. Whether you are choosing your first ISP or searching for a better or cheaper one, finding the right service provider can be a challenge.

First you will want to decide what type of Internet service you want to use. There are basically two types. A dial-up connection that uses your current telephone line to connect to the Internet has many drawbacks. It is the slowest type of service. It ties up your telephone line unless you install an extra line or a device to notify you when a call comes in while you are online. It can take several minutes to make a connection. The only advantage of dial-up service is the cost. It is the cheapest way to get on the Internet. So dial-up service may be an option if cost is an important factor or if you only plan to use the Internet on an occasional basis.

For those of you who want to go online regularly and don't mind spending more, broadband Internet access is the way to go. It is fast, doesn't tie up your telephone line, and is "always on" so you don't have to wait for the telephone to dial and connect. When your computer is on, the Internet is instantly available to you. There are three popular types of broadband connections: DSL, cable, and satellite. To learn more about each of these read my Moving to Broadband article.

For more general information about the different types of Internet connections, read How to Differentiate Between Internet Connections.

Once you have decided which type of connection you want, it is time to start your search for an ISP. An Internet Service Provider can be a company like Earthlink or America Online. These are dedicated ISPs that are only in the Internet business. It can also be a telephone company like Sprint, or a cable company like Time Warner. Dedicated ISPs and telephone companies can provide both dial-up and broadband service while cable providers generally only provide broadband cable connections. First check with your own cable service provider and telephone company. Call or visit their Web sites to compare prices and service. Then check out any dedicated Internet Service Providers. You can often locate local service providers through ads in your local newspaper. You can find national service providers by searching the Internet and/or computer-related magazines and material.

While price is important, don't choose an ISP based solely on the amount that it charges or you may be disappointed when you cannot get online or get help. In choosing an ISP you should not underestimate the importance of the quality of service and the availability of good support. Often the only way to evaluate these services is to get the opinion of and learn from the experiences of others. So talk to your friends, relatives, and neighbors. See if they are happy with their ISP.

Web sites like Broadband Reports at www.broadbandreports.com will help you figure out what services are available in your area and also have message boards where people tell about their experiences, often praising or condemning their broadband services. Reading these individual reviews is an eye-opening experience that you will want to have before you decide which service you want to use.

When investigating Internet Service Providers you will want to find out what actually comes with your account. Most provide the software you need and will help you set up your computer so that you can make the Internet connection for the first time. Many have toll-free numbers and unlimited technical support. Two things that can vary are the number of e-mail accounts the service provides and the amount of Web storage space that comes with your account. If you are getting a dial-up connection, you will need a modem in your computer (most of today's computers have them pre-installed). To use a broadband connection you will need an external cable or DSL modem. This is usually provided and owned by the ISP and is provided as part of the service, but sometimes there is an additional charge for equipment. So be sure to ask about the equipment. Except for an inexpensive telephone cord, there is no installation cost for a dial-up connection. You simply hook your computer up to your telephone line. Installation for broadband connections is more complicated and must be provided by the ISP. Installation costs can also vary; another thing to check out.

If you travel, be sure that the Internet service you are considering provides dial-up access that you can use without long distance charges, just in case you want to check your e-mail while you are away. When comparing broadband service, be sure to check the amount of upload and download bandwidth that each service provides. Also, be aware that sometimes you can get very similar services by two different companies. For instance, if you are in an area serviced by Time Warner cable, the Earthlink Internet service will use the Time Warner backbone for your service. So the physical service will actually be identical. However, the Earthlink cable and the Time Warner Road Runner, the Time Warner cable Internet service, may offer different prices, different installation charges, and different incentives, so you will want to compare them.

The contract that you agree to is also important. Are you signing up for a certain period of time? Can the service be terminated without penalty? Remember, when deciding which company to use for your Internet service, customer service, availability, quality, and responsiveness is very important. There is certainly a lot to investigate when choosing an ISP, but a thorough scrutiny of the ISP and the services they offer will help you make an informed decision that will make you smile for months to come.

source:http://www.aarp.org

Mixing VISTA and XP on network to work properly

2009-01-05T09:35:00.000-08:00

When you combine Windows XP and Windows Vista PCs on the same peer-to-peer network, such as you might have at home or a small office, you may run into all kinds of problems. It may be difficult for your Windows Vista PCs to find your Windows XP PCs, and vice versa. And the Windows Vista Network Map which may be the best networking feature Microsoft has ever introduced into Windows won’t work properly with XP PCs. They won’t show up properly on the network map, if they even show up at all.

The first problem is that the default name for your workgroup on the network has been changed from Windows XP to Windows Vista. In Windows XP, the default name for the network is Mshome; in Windows Vista, it is Workgroup.

The fix for this problem is easy; you can change the name of the workgroup on Windows XP to match the name of your Windows Vista network. On Windows XP, right-click My Computer, click the Computer Name tab, then click Change. The screen shown nearby appears. In the Workgroup box, type in the name of your Windows Vista network name. If you’re leaving it as the default used in Windows Vista, type in Workgroup. If you’re not using the Windows Vista default, change it to whatever name you’ve given your Windows Vista network and click OK.

After you click OK, you’ll see the confirmation dialog shown in the figure below. Click OK again, then restart your PC.

You can, instead, give your Windows XP and Windows Vista machines both new workgroup names, as long as they match. To change the name of your workgroup in Windows Vista, right-click Computer and select Properties. You’ll see the name of your PC as well as its workgroup name. Click Change Settings, then from the screen that appears, click Change. In the dialog box, shown in the figure below, type in the new name for your workgroup and click OK.

As with Windows XP, you’ll get a confirmation that the name has been changed. You’ll have to restart your PC for the changes to go into effect.

Patching Windows XP for Vista network compatibility

Making sure that both Windows XP and Windows Vista are on the same workgroup will go part way toward making the PCs get along on your network, but won’t go all the way. A bigger problem has to do with the new Windows Vista network map.

The network map is possibly the best addition it comes to networking that Windows Vista has made. To get there, select Control Panel –> Network and Internet –> Network and Sharing Center –> View full map. A screen like one below appears.

The map shows you all the PCs and devices attached to your network — those in your entire network, not just your workgroup. This map is more than nice to look at; it’s extremely useful as well. Hover your mouse over any device, and you’ll be shown information about it, such as its name, IP address and MAC address, as shown in the figure below. Click a PC and you’ll connect to it.

There’s a rub, though. Look at the bottom of the screen in the network map Vista drew of our network. You’ll see a number of devices listed. Windows Vista has found them, but doesn’t quite know what to make of them. It can’t figure out where they fit in on the network. And it won’t give you any information about them if you hover your mouse over them.

The problem is that to discover information about devices, Windows Vista uses a new protocol, called Link Layer Topology Discovery. LLTD is built into any Windows Vista PC, which is why they show up properly on the network map. However, LLTD isn’t built into Windows XP, which is why they don’t show up properly.

You can fix the problem by downloading and installing the Layer Topology Discovery Responder. Install it and your Windows XP PC will show up on the network map, properly located, with the mouse hover in full working order, as you can see in the figure below.

resource : pctipsbox.com

How to chose the best Access Point (AP)

2009-01-05T08:51:00.006-08:00

Today the market is flooded with a range of wireless access points. There are dozens of important features to consider, so much variation in cost and several different performance parameters, that it can become quite confusing to decide which one is right for you. To address most of these concerns, we ripped apart 13 wireless access points with a barrage of tests, and analyzed them for over a dozen features. You'll find their individual reviews in the subsequent pages, followed by a table comparing the important features as well as the performance results. These include eight access points of 802.11b and five of 802.11g standards. But, before that, we'll look at the important features that should be considered when buying an access point, followed by the performance parameters. All performance and features parameters discussed here, along with the price and warranty of each access point, have been included in our analysis for the shootout. As usual, we used the Brown-Gibson model to arrive at the weightages for these parameters.

Which standard?
Speaking of standards, it's still not legal to use 802.11g-based products without a license. Only 802.11b based ones can be used indoors freely. While it's not very expensive to obtain a license, it's a long drawn process. Alternatively, you could go for an 802.11b access point that's upgradable to the g standard, apply for a license and then upgrade once you get the license. It's, therefore, an important feature to consider when going for an 802.11b access point. If you have a license or don't mind putting in the effort to get one, then you could also go for 802.11g based access points as they have a maximum throughput capability of 54 Mbps, unlike 802.11b that can deliver only 11 Mbps. Plus, the g standard is backward compatible with b, so even if you have b based wireless clients, they would still work, albeit at 11 Mbps.

How much security?
Security has always been a concern in wireless networks, so it's important to check out the security features of an access point before you buy it. First, define the level of security you need in your setup. For instance, if your office is in a crowded area and the chances of your WiFi signal going out of your premise is high, then it's better to go for tighter security because it would be easy for someone from outside to misuse your WiFi network. What level of accessibility are you planning to provide through your WiFi network to your mobile users? Is it just to surf the Net or will they also be able to access your servers? There are various security modes providing different levels of protection. The most basic is WEP (Wireless Equivalent Privacy) encryption, which is present by default in all access points. But, Wireless Equivalent Privacy has been found to be weak and, therefore, not always suitable for security a WiFi network. Look for other security modes, such as MAC-address based filtering, Radius-based authentication and WPA before you go out on your hunt for the right access point.

Modes of operation
Most access points can be used in more ways than one, but this functionality varies across vendors. Besides working as a standard access point, it can also work as an access point-to-access point bridge, repeater, gateway and more . Having more modes of operation gives an organization the flexibility to use the access point in any way they need. So, support for more modes is always better.

Management features
How easy is it for you to manage your access point? Most of them provide a Web-based interface for management, but that's not enough. Look for more management features available in this interface. Does it support SNMP, so that if you have your network management software running in your organization, it can easily be added in? Is it simple support for SNMP or can you also set traps for certain conditions so it sends out information to the administrator every time there's a problem? What other information can the access point provide? Does it maintain log files of all system activity? What level of activity can it put in the log file? What kind of statistics can it display about itself? The more management features it has, the easier it will be on the network administrator.

Load balancing and fault tolerance
If the number of users connecting to a particular access point with load-balancing support increases beyond a predefined limit, it will shift some users to a nearby access point. This feature can be useful if you have high user density per access point. So, look for one that supports load balancing. Fault tolerance, of course, means that if one access point goes down due to some reason, then the clients connecting to it should be diverted to another access point.

Other features
There are several other features that need to be considered. One is automatic channel selection, which becomes important if you're deploying lots of access points. This way the administrator doesn't have to manually define each channel, thereby reducing chances of human error. Can the antenna of the access point be upgraded to a different type or of higher power? What kind of software ships with the access point? How useful is it when deploying WiFi? Does the access point support power over Ethernet? This can be useful if you're placing an access point where you don't have a power connection nearby.

What about the quality of the power adapter itself? We noticed that several access points still shipped with the bulky transformer-based adapters. Today, most devices come with the lightweight, SMPS-based adapters, which have a longer life because they consume lesser power and generate lesser heat. So, an SMPS-based adapter is always preferable over transformer based one.

Performance parameters
There are a number of parameters that we considered for performance. For measuring all data transfers, we used NetIQ's Qcheck benchmark. The tests are as follows:

Max range: What's the maximum distance that a client can go from an access point without loosing connectivity and also be able to transfer data? While doing this test, we ensured there were no obstructions between the access point and the client. We stopped measuring beyond 200 mtrs as only a few Access Points showed connectivity beyond that distance.

Max range with max signal strength: While the signal strength of an access point reduces with distance, up till what distance can an access point keep it in excellent condition? The higher this is, the better.Here again we stopped measuring beyond 150 mtrs for same reasons as above.

Max throughput: For clients connected in close vicinity to the access point, what's the maximum throughput that it can offer? Surely, it's impossible to obtain 11 and 54 Mbps, the maximum theoretical limits of 802.11b and g standards, respectively. So, we measured the maximum that each access point could provide with a client when:

*It used a WiFi card from the same vendor.
*It used a third-party WiFi card. Most laptops shipping today are Centrino based, which means that they use an Intel WiFi card. For this test, we used a Centrino-based laptop.

Latency: We measured the average latency between the client and the access point while transferring some data. Here, lower latency is better.

Throughput with streaming data: This becomes important when you're using WiFi for applications that require a constant stream of data without any break., like voice and video apps. For this, we configured the test to maintain 1000 Kbps for 15 seconds.

Resistance to interference: The 2.4 GHz frequency band that's used by all these access points is susceptible to interference from other devices like cordless phones and Bluetooth. We checked how susceptible was an Access Point to such interference by measuring the throughput with a Bluetooth device in between.

A few tips Finally, here are a few tips to keep in mind.

*Please check that the features mentioned on the packaging of your access point are actually there. In one access point we found the packaging said 256 bit WEP encryption, while it actually only supported 128.
*Before setting up an access point, read the instructions carefully. Some access points provide a MAC address that has to be entered during the installation.
*Place the access point where there's minimum interference from other devices. Usually, it's advisable to place it near the ceiling.
*Many access points specify how to position their antennas, so please check the manuals for that. Don't tamper with the antenna when it's working.
*Coexistence of 802.11g and 802.11b wireless clients on the same wireless network could slow down your network performance. So, when upgrading to 802.11g, also try to shift your clients to the same.

Lastly, there's a wide price variation that we found in all the access points, ranging from Rs 8,000 to Rs 52,000. So, choose carefully, depending upon the features you want.

resource : pcquest.ciol.com

How To Maximize Or Increase The Speed Of Your Wi-Fi Connection

2009-01-05T08:25:00.000-08:00

Today, enterprises are deploying wireless LANs for corporate applications and home users that involve e-mail, Web browsing, and access to various server-based databases. The need for higher data rates and techniques to improve performance of wireless LANs is becoming crucial to support these types of applications. To get that extra performance, you may have a lot to consider.

Select The Right Physical Layer

An important element that impacts the performance of a wireless LAN is the selection of the appropriate Physical (PHY) Layer (i.e., 802.11a, 802.11b, or802.11g). 802.11a offers the highest capacity at 54Mbps for each of twelve (maximum) non-overlapping channels and freedom from most potential RF interference. 802.11b provides 11Mbps data rates, with only three non-overlapping channels. 802.11g will eventually extend 802.11b networks to have 54Mbps operation, but the three non-overlapping channels limitation will still exist. Of course requirements dictate needs for performance, which will point you toward a particular PHY. If you need maximum performance, then 802.11a is the way to go, but you may need more access points because of the weaker range it has compared to 802.11b.

MIMO ANTENNA

If you are using 802.11g – consider getting an MIMO antenna (which allows faster speeds at greater distances.)

Replace Other 2.4 GHz Devices

You may need to replace your 2.4GHz cordless phones with either a 900Mhz or 5.8GHz style cordless phone due to interference. These phones and other nearby wireless LANs can offer significant interfering signals that degrade the operation of an 802.11b wireless LAN. These external sources of RF energy in the 2.4GHz band periodically block users and access points from accessing the shared air medium. As a result, the performance of your wireless LAN will suffer when RF interference is present. So obviously you should strive to minimize sources of RF interference and possibly set the access point channels to avoid the interfering signals.

Properly Set Access Point Channels

The 802.11b standard defines 14 channels (11 in the U.S.) that overlap considerably, leaving only three channels that don’t overlap with each other. For access points that are within range of each other, set them to different channels (e.g., 1, 6, and 11) in order to avoid inter-access point interference. You can also take advantage of the automatic channel selection features that some access points offer. With 802.11a, this is not an issue because the 802.11a standard defines separate, non-overlapping channels.

Maximize RF Coverage

If access points are too far apart, then some users will be associating with the wireless LAN at something less than the maximum data rate. For example, users close to an 802.11b access point may be operating at 11Mbps; whereas, a user at a greater distance may only have 2Mbps capability. In order to maximize performance, ensure that RF coverage is adequate and spread out nearby for optimum performance.

Same Router And Network Adapter

Choose your router and network adapters from the same company. Manufacturers usually have a proprietary “turbo” mode that only works when using both their router and network adapters. As a side benefit; your overall configuration is usually easier.

Upgrade Your 802.11b

Upgrade your 802.11a and 802.11b devices to 802.11g, which is much faster, and is backward-compatible with 802.11b devices, although a small one room environment (i.e. apartment, dorm room) with no future expansion should use 802.11a.

Wired Connection

Whenever possible, connect computers using a wired connection! Yes, this is an “Anti-tip” because you’re not even using the wireless network – but a direct connection is dramatically faster and more secure!

Wireless Router On Central Location

If possible, place your wireless router (or access point) in a central location. Obviously, the closer you are to the access point; the better. But do not necessarily place the device on your roof (or up too high) – 4 to 6 feet off the ground is perfect.

Update Your Windows Wireless Network Driver

Update your Windows Wireless Network Driver. While Microsoft Update, is “supposed” to notify you of updates to your drivers – it’s best to visit the manufacturers website to double-check. Updates usually only add a new feature, or increase stability and security; but sometimes can improve performance.

Update And Upgrade Your Router

Update your Router’s firmware. Most routers easily update their firmware directly from their software. Updates add new features, increase stability and security; and also sometimes help in improving the performance. The antenna that comes with your device is usually a low powered and omni-directional. Upgrade to a more powerful (powered) antenna. If your router is near an outside wall, get a high-gain antenna that focuses the wireless signals only one direction.

resource : www.addictivetips.com

Network command in unik/linux, windows or mac OS

2008-12-25T02:06:00.000-08:00

The following commands will report the TCP/IP configuration on Unix, MacOS X, Windows, and Cisco operating systems. By "Unix" I mean anything vaguely Unix-like — Solaris, Linux, BSD, Tru64, AIX, IRIX, HP-UX, etc., plus MacOS X.

Note that the Cisco IOS allows for command abbreviation. That is, instead of:
router> show interfaces
you could simply type:
router> sh in
However, I prefer to use the entire command, using the tab key for command completion. You type just sh and then press :
router> sh
and the system finishes the command itself:
router> show
At that point you could press ? to see what alternatives are available (in the case of the show command, quite a few!), and then type enough of the parameter to be unambiguous:
router> show in
and it finishes the parameter for you:
router> show interfaces
Only two more key presses and you get a clear explanation of what it's doing. More importantly, your typing errors become much more obvious!

WINDOWS IP CONFIG

2008-12-25T01:55:00.000-08:00

Configure IP (internet protocol configuration)

Syntax

IPCONFIG /all = Display full configuration information.
IPCONFIG /release [adapter] = Rlease the IP address for the specified adapter.
IPCONFIG /renew [adapter] = Renew the IP address for the specified adapter.
IPCONFIG /flushdns = Purge the DNS Resolver cache.
IPCONFIG /registerdns = Refresh all DHCP leases and re-register DNS names.
IPCONFIG /displaydns = Display the contents of the DNS Resolver Cache.
IPCONFIG /showclassid adapter = Display all the DHCP class IDs allowed for adapter.
IPCONFIG /setclassid adapter [classid] = Modify the dhcp class id.

If the Adapter name contains spaces, use quotes: "Adapter Name"
wildcard characters * and ? allowed, see the examples below

The default is to display only the IP address, subnet mask and default gateway for each adapter bound to TCP/IP.

For Release and Renew, if no adapter name is specified, then the IP address leases for all adapters bound to TCP/IP will be released or renewed.

For Setclassid, if no ClassId is specified, then the ClassId is removed.

Examples:
> ipconfig ... Show information.
> ipconfig /all ... Show detailed information
> ipconfig /renew ... renew all adapters
> ipconfig /renew EL* ... renew any connection that has its
name starting with EL

> ipconfig /release *Con* ... release all matching connections,
eg. "Local Area Connection 1" or
"Local Area Connection 2"

> ipconfig /setclassid "Local Area Connection" TEST
... set the DHCP class ID for the
named adapter to = TEST

"Life is a grand adventure - or it is nothing." - Helen Keller

Related:

BROWSTAT - Get domain, browser and PDC info
NETSTAT - Display networking statistics (TCP/IP)
NETSH - Configure interfaces, routing protocols, filters, routes, RRAS
PATHPING - IP trace utility
PING - Test a network connection
Q192064 - Locate multiple preferred logon servers
Q813878 - How to block specific network protocols and ports.
Q313190 - Use IPSec IP Filter Lists
The Inq/Jon Honeyball - Routing to harden machines against attack
www.ipchicken.com
Equivalent bash command (Linux): lookupd -flushcache, ifconfig - IP configuration
Equivalent bash command (OS X): ipconfig / dscacheutil - View IP config / Query / flush the Directory Service cache

resource www.ss64.com

WIRELESS HACK

2008-12-23T17:59:00.000-08:00

Ever wondered just how secure your WEP protected wireless network is? Well today I'll show you how to test it. There have been a lot of articles written about this subject already and by now it is common knowledge that WEP is only the barest of security precautions. I'm going to show you how you can test your own wireless network's security using the linux livecd distro back|track. Before we go any further, I feel it necessary to mention two things. The first being the ethics of hacking. Most of you are probably familiar with this subject already but, just to refresh your memory. Second, it goes without saying that this is for YOUR OWN NETWORK TESTING PURPOSES ONLY. Unauthorized access of other people's networks is illegal. If you have problems or questions about anything in this guide, for the love of god use google/wikipedia and look it up first. Don't just start ranting on forums like a moron without doing a little research first. There are probably other people who have had the same problems and solved them already. Ok, parental rant over. Lets get down to the dirty stuff:

First of all, you'll need to check and make sure your wireless card has the right chipset. Most wireless cards are programmed only to accept data that is addressed to them. Other cards, specifically the ones that are of use for wifi sniffing, are capable of picking up all traffic that is flying through the air. Common types are Atheros, Prism, Aironet, Realtek, Hermes, etc based cards. You are on your own figuring out what type of chipset your wireless card has, as its too vast to get into here, but check this thread for more info. Your probably just going to have to search for your specific card to find out what chipset it has then compare it to this compatability list. For a good discussion on types of cards that work, check this http://forums.remote-exploit.org/showthread.php?t=2191

Next, download a copy of back|track, a slackware distro designed for security testing purposes. This is a linux livecd, which means it will boot the entire OS from the cd. Download the ISO and use a burning program such as Nero, Alcohol or my personal favorite, the awesome freeware cd/dvd burning program cdburnerXP to burn the disk image to a cd. Pop the disk in and reboot, and boot from the disk. Back|track may take a while to boot up.

When back|track boots up (and hopefully finds all your hardware) you will be presented with a login screen. To quote the venerable xatar, "Read the f**king screen!" The login, as it says above the prompt is "root" and the password is "toor" (minus the ""). Note that linux is case sensitive. After you are logged in, you could run all of the commands I will get into later from this prompt. But thats no fun, so type in:

xconf

This should create a file /etc/X11/xorg.conf and autodetect your video settings. (with nvidia cards, you may still have video problems as I did, such as not getting above 640x480... should you choose to install backtrack to the harddrive, check out http://forums.remote-exploit.org/showthread.php?t=2176&highlight=nvidia for more info on fixing this)

To get the KDE gui desktop to start up, simply type:

startx

If everything goes smoothly, you should be awash in the beautiful glow of the back|track KDE desktop. Given the beautiful read only nature of the livecd, you can do anything to this operating system and not have to worry about messing it up. If things get a little weird, or screwed up, just reboot and the OS is back to normal. So GO EXPLORE, run random programs, see what they do, go nuts.

At the bottom left of the screen is a little icon that looks like a monitor with a black screen. This is called the bash prompt. This is where you will be spending most of your time, so click on this to open up a new bash prompt. Note that you can double click on the bar to the right of the tab that says "Shell" and it will create a new bash tab, negating the necessity to open up multiple instances of the bash window. First, a few networking commands to get you up to speed on your own system. Type

ifconfig -a

ifconfig

This will show you a list of all compatible network cards on your system. You should see a list of devices such as ath0, eth0, wifi0, wlan0 etc. One of these is your wireless card. If you have an Atheros based card, it will be ath0. Make note of the name of your card, as you will be using it later. For the rest of this guide, I will be using ath0 since that is the card I have. Replace ath0 with whatever card you have.

You can also check out your wireless cards specifically by typing in:

iwconfig

I've got two wireless cards. The one built into my laptop, an intel card (eth0) and an Atheros pcmcia card (ath0). Now that we have the name of our wireless cards, we can start sniffing. Some like to use Kismet to sniff for networks, but I find using airodump-ng to be easier and ultimately more effective. In your bash prompt, type:

airodump-ng --write out --ivs --abg ath0

This starts airodump-ng and tells it to begin sniffing data, write it to the file out, only capture IVs (Initialization Vectors), search the a, b and g bands using the ath0 card. Keep in mind, every time you specify the same output file name, such as "out", airodump-ng will append the file name with "-##" such as out-01.ivs, out-02.ivs, etc.You will see a list of access points on the top half of the screen, and clients on the bottom. Find your access point in the list. Write down the BSSID or Mac address of the access point and any connected clients. You'll need it later. From now on in this document, the access point's mac address will be referred to as APmac and the client mac as CLmac. The goal of the attack is to capture as many unique IVS as possible. Every time data is sent between the wireless server and client, each packet contains IV which are collected and then run through the aircrack-ng program for computation.

You should be seeing a ton of numbers flying by, but not updating vary quickly. Thats because airodump-ng is searching all channels. Once you see your network, note what channel it is on (under the CH header). Stop airodump-ng by hitting:

ctrl-c

Now start it up again but this time we will add --channel # where # is the channel number of the access point, say, channel 6

airodump-ng --channel 6 --write out --ivs --abg ath0

airodump

Airodump-ng should be running much faster now, and updating constantly. You will see a number rising very quickly, this is generally the beacons. Beacons just basically say "hey, i'm an access point" about 10 times a second. You can judge the quality of your connection by how fluid the rise in beacons are. Other than this, they are useless for our purposes. For this type of attack it is important for there to be a client connected to the access point. So march over to your other computer and log on to the net wirelessly. In backtrack, you should see at the bottom a client pop up, the first MAC is the access point and the 2nd is the Client. Write down both. Open a new bash prompt and type:

aireplay-ng -2 -b APmac -d ff:ff:ff:ff:ff:ff -m 68 -n 68 -p 0841 -h CLmac ath0

aireplay

Where APmac is the mac address (bssid) of the access point and CLmac is the mac address of the client. For a detailed explanation of what all these settings do, open up a new bash prompt and just type aireplay-ng and it will spew out all the controls and what they do. The only one not explained is that the very first -2 tells aireplay to do the 3rd attack method in the list at the bottom (the first being 0).

aireplay-ng will now start sniffing for a certain type of packet with a length no more and no less than 68 bytes between client and access point. It will say "Read ### packets". At this point, if there is significant data transfer between the client and ap, it may snag the right type of packet already and there is no need to do the next step. In this case, hit Y to use the packet and skip the next step. If however, it keeps reading packets for a while (more than a couple min) and does not pop up saying "Use this packet?" then do the following:

Open a new bash prompt and type:

aireplay-ng -0 1 -a APmac -c CLmac ath0

This command will effectively terminate the connection between the AP and the client forcing the client to re-connect. It is this re-connection packet that we are looking to scoop up with the first instance of aireplay.

Go back to the first instance of aireplay and you should see something at the bottom of the screen saying "Use this packet?" Hit Y and aireplay will start sending out tons of packets to the AP. Switch over to airodump-ng which should still be running in the first bash prompt. Look at the data rate of the targeted AP. If all is going well, Aireplay is spewing out packets like mad to the access point and airodump-ng is picking up the chatter in between, the data should be rising quickly. This is exactly what we want.

If for some reason the data isn't going up quickly, go back to the first aireplay-ng and hit:

ctrl-c

If aireplay had picked up any more packets, it will prompt you again if you want to use them. Try more packets. Also, you may need to get closer to your access point or try the aireplay-ng -0 method again. Experiment. Once you've got the data rate going up quickly, start aircrack-ng and start crunching the numbers. Type in

dir

To get a list of the files. One file should be the out file that you specified in airodump-ng, specifically out-01.ivs. Each time airodump-ng is started with the same file output name, it creates a new one tacking on -01, -02, etc. Make sure you know which one you are outputting to.

Type in:

aircrack-ng -f 2 -a 1 -b APmac -n 64 out-01.ivs

Again, if you want to know what all the parameters mean, open up a new bash and type aircrack-ng and it will tell you. Basically -f is the fudge factor- default is 2, a higher number will be a more thorough but slower search. -b filters out all but the specified mac of the AP, -n says to search for a 64 bit key. If it runs for a long time and finds nothing, either you don't have enough IVs, or you are searching under the wrong key length. Try 128. You can also run multiple instances of of aircrack with different variables. Aircrack will continually update, notice the increasing IVs in the upper right as long is airodump-ng and aireplay are still going strong. After a bit of time, it should spit out your WEP key. Congrats! You now know how hard it is breaking into YOUR OWN NETWORK. Perhaps switch to WPA? If it didn't work, there could be any number reasons why. Do a little searching on the backtrack forums, google, etc, try setting up a different access point or learn how to do another type of attack, learn how to configure your hardware properly, etc, etc, etc. Take your time and explore the OS, if your new to linux, like i was when i started using backtrack, you'll have a lot to learn.

As a side note, In order to connect to a wireless network in backtrack, you must type in

iwconfig ath0 essid nameofnetwork key whateverthekeyis

ifconfig ath0 up

dhcpcd ath0

A message should pop up in the bottom right of the screen saying something about ath0 being connected. To disconnect, before switching to another network, type:

ifconfig ath0 down

then repeat the steps above with the new network information.

Further reading: http://www.cs.wright.edu/~pmateti/InternetSecurity/Lectures/WirelessHacks/Mateti-WirelessHacks.htm

I'd like to thank muts, max, redkommie, jacky, digi, creaters of backtrack, xatar for writing a lot of the guides that got me up to speed, the creators of aircrack-ng and all the awesome people on the rexploit forums.

resource: www.i-hacked.com

GOOGLE ADSENSE

2008-11-20T09:47:00.000-08:00

Google AdSense is the program that can give you advertising revenue from each page on your website—with a minimal investment in time and no additional resources.AdSense delivers relevant text and image ads that are precisely targeted to your site and your site content. And when you add a Google search box to your site, AdSense delivers relevant text ads that are targeted to the Google search results pages generated by your visitors’ searc request.

Setting Up Google Adsense Code

Since its inception, The Google AdSense has created considerable hoopla all over the world and opened a plethora of opportunities for people interested to earn online in an alternative way. However, a person should know the process of Setting Up Google Adsense properly to reap in maximum profits.

For Setting Up Google Adsense account and start earning, one needs to learn some basic steps. The first step a person requires to learn is the way to generate from his account the AdSense code. It is also imperative for a person to learn how to deal with the settings and appearance of his ad units from his accounts. He also needs to know the way to paste the ad code properly and get his article published on the Internet. For doing these, one needs to create an account with ‘HowToDoThings’.

One can take the help of the AdSense guide called ‘HowToDoThings’ for both Setting Up Google Adsense account and fine-tuning an already existing AdSense account. If one wants to make a Google Adsense account from the scratch successfully he should log in to the site of ‘HowToDoThings’. Thereafter, he should browse his contributor dashboard. Next, he should select “My Google AdSense Info” located on the left side of the page.

On doing so, the person will get a message saying that he does not have any Google AdSense account related with his HowToDoThings account. Clicking on the link will activate the AdSense account opening process. Here, the person is required to provide a valid e-mail address. In the next step, he will have to go through the conditions and terms laid by Google, which is an important part.

After reading the terms, he should click on ‘Sign Me Up’. Shortly after this, he will get a message confirming that an account has been created for him. It will also instruct the person to see his mailbox to receive further notifications. The Google email instructions need to be executed to activate the account.

In case, a person already owns a Google Adsense account he can link it with HowToDoThings. That way he can start getting article revenue quickly. This procedure is quite similar to Setting Up Google Adsense account from the scratch. A person needs to have a valid Google email id. Google informs the user after his HowToDoThings dashboard gets linked with AdSense and provides instructions for activating the account.

MAKE WAJAN BOLIC ANTENNA

2008-11-19T07:07:00.000-08:00

Introduce
Basicly the function of this wok is being wave reflector like parabola. More bigger of the wok more strong the wave we can get. This antenna can connect on the rang 1-1,5 km.

Make USB WIFI ANTENA USB (Wajanbolic)
ENGLISH VERSION

Material
1. Big diameter of wok(more bigger more better)
2. PVC pipe with diameter 3 inch.
3. Doff 3″ (to close the top of PVC paralon) 2 piece
4. Aluminium foil
5. bolt wit size 12 or 14
6. Wifi USB Adapter
7. Double tape
8. UTP cable 10 meter
9. Pole (to make antenna more high)

Equipment
1. Ruler
2. Cutter

Procedure
1. Make the hole on the wok
2. Make USB ekstension with UTP cable
Calculate the focus of the wok D:diameter d:depth of the woke
F = D^2/(16*d) = 70^2 / (16*20)

example:

Parabolic dish with D = 70 cm, d = 20 cm
Distance focus from center dish : F = D^2/(16*d) = 70^2 / (16*20) = 15.3 cm

Cut the PVC pipe 30 cm, then give a mark for the distance of the feeder (free aluminium foil area).

1. Make the hole on pipe and don’t forget on the mark of focus to take Usb Wifi adapther
2. Then wrap pipe with aluminium foil except the feeder, if the alumunium foil doesn’t have a glue, use double tape.
3. Take the doff to close the pipe.
4. Then take first doff on hole of the wok. Then use the bolt and rool it.
5. Take the pipe on the doff.
6. Make 10 meter usb ekstension with UTP cable. Cut the short ekstension then open the cable. Choose the color of UTP and pair with the short USB ekstension. Nop roblem if u choose diferent color but you have to do again for the other point. With the same color of pair.example usb red>utp brown, usb blueutp green.
7. Connect the Usb ekstention with usb wifi. Take the antenna on the top of pole. Connect the ekstention cable to the computer and scan the wireless network.
8. When it’s connect you are ready to browsing, surfing, and wardriving.
pic. Tutuppancibolic (close with usb wajanbolic)

MAKE WAJAN BOLIC ANTENNA

2008-11-19T06:46:00.000-08:00

PENDAHULUAN
Pada umumnya peranan wajan (parabolic) adalah sebagai reflector, atau pemantul gelombang. Yang kemudian gelombang tersebut dipantulkan dari semua sisi wajan dalam satu titik yang dinamakan focus dengan tujuan sinyal semakin kuat. Dapat kita ambil dalam reflector lampu senter, sinar yang berada pada titik focus lebih terang daripada titik yang lainnya, begitu pula pada fungsi wajan bolic ini. Kesimpulannya Semakin besar wajannya semakin butuh banyak minyak gorengnya(hex2..)

BAHAN

1. Wajan diameter 36″ (semakin besar diametr semakin bagus)
2. PVC paralon tipis diameter 3″ 1 meter
3. Doff 3″ (tutup PVC paralon) 2 buah
4. Aluminium foil
5. Baut + mur ukuran 12 atau 14
6. Wifi USB Adapter
7. Double tape + lakban
8. Kabel utp 10meter
9. Tiang besi atau apabila budget mpet ya tiang bamboo(untuk meninggikan antenna, lebih tinggi dari bangunan)

PERALATAN

1. Penggaris
2. Pisau/ Cutter
3. Gergaji besi

PERKIRAAN HARGA

Wajan tempat penggorengan kira-kira sekitar Rp.45.000, Terus yang penting USB wirelesnya Rp.250.000 peralon 3 inc 1meter Rp.20.000, Kabel Utp (sebagai ekstensi usb) 10meter Rp.25.000. Bahan-bahan yang lain tidak dihitung dikarenakan harga murah dan mudah didapat.

TAHAP PENGERJAAN

1. Siapkan semua bahan dan peralatan yang dibutuhkan.
2. Lubangi wajan tepat di tengah wajan tersebut seukuran baut 12 atau 14, cukup satu lubang saja.

Kemudia, ukur diametr wajan, kedalaman wajan dan feeder/ titik focus. Untuk lebih jelas nya silahkan liat gambar di bawah.

Parabolic dish dg D = 70 cm, d = 20 cm

maka jarak titik focus dari center dish : F = D^2/(16*d) = 70^2 / (16*20) = 15.3 cm(ket :^àpangkat, *àkali, /àbagi)

Pada titik focus tsb dipasang ujung feeder. Untuk mendapatkan gain maksimum.

1. Potong PVC paralon sepanjang 30 cm, kemudian beri tanda untuk jarak feeder nya (daerah bebas aluminium foil). Untuk menentukan panjang feeder nya gunakan rumus di atas.
2. Beri lubang pada focus bagian paralon untuk meletakkan Usb Wifi
3. Selanjut nya, bungkus PVC paralon dengan dgn aluminium foil pada daerah selain feeder, klo aluminium foil yang ada tanpa perekat, maka untuk merekatkan nya bisa menggunakan double tape
4. Dan pasangkan doff tersebut ke PVC paralon
5. Kemudian, wajan yang telah di lubangi tadi dipasangkan dengan doff yang satu nya lagi, sebelum nya doff tersebut dilubangi sesuai dengan ukuran bautyang sudah di siapkan, dan kencangkan secukup nya.
6. Kemudian tinggal pasangkan PVC paralon tadi ke wajan yang sudah di pasang doff.
7. Buat Usb Ekstensi perpanjangan 10 m dengan UTP kabel caranya: Potong kabel perpanjangan menjadi 2, satukanlah masing-masing kabel perpanjangan dengan kabel UTP (pilih empat kabel saja) lakukan di ujung yang lain (jangan sampai menyatu) dengan catatan warna kabel dengan pasangan harus sama dengan ujung lainnya. Agar tidak terjadi kesalahan catat. Missal, usb biruàutp hijau, usb kuningà utp coklat. Lakban sambungan kabel tersebut.
8. Sambungkan USB dengan perpanjangan USB yang dibuat tadi. Pasangkan di tiang peninggi. Tancapkan kabel USB kekomputer dan scan wireless network.
9. Wajan bolic sudah siap untuk digunakan browsing, atau paling tidak untuk wardriving.

Gb. Tutuppancibolic (hampir sama dengan wajanbolic)

WINDOWS 7

2008-11-17T16:45:00.000-08:00

Windows 7 (formerly codenamed Blackcomb and Vienna) is the next release of Microsoft Windows, an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops, Tablet PCs, and media center PCs.

Microsoft stated in 2007 that it is planning Windows 7 development for a three-year time frame starting after the release of its predecessor, Windows Vista, but that the final release date will be determined by product quality.

Unlike its predecessor, Windows 7 is intended to be an incremental upgrade with the goal of being fully compatible with existing device drivers, applications and hardware.Presentations given by the company in 2008 have focused on multi-touch support, a redesigned Windows Shell with a new taskbar, a home networking system called HomeGroup,and performance improvements. Some applications that have been included with prior releases of Microsoft Windows, most notably Windows Mail, Windows Movie Maker and Windows Photo Gallery, are no longer included with the operating system; they are instead offered separately as part of the Windows Live Essentials suite.

In 2000, Microsoft started the planning to follow up Windows XP and its server counterpart Windows Server 2003 (both codenamed Whistler) with a major new release of Windows that was codenamed Blackcomb (both codenames refer to the Whistler-Blackcomb resort). This new version was at that time scheduled for a 2005 release.[6][7]

Major features were planned for Blackcomb, including an emphasis on searching and querying data and an advanced storage system named WinFS to enable such scenarios. In this context, a feature mentioned by Microsoft co-founder Bill Gates for Blackcomb was "a pervasive typing line that will recognize the sentence that [the user is] typing in."[8]

Later, Blackcomb was delayed and an interim, minor release, codenamed "Longhorn", was announced for a 2003 release.[9] By the middle of 2003, however, Longhorn had acquired some of the features originally intended for Blackcomb, including WinFS, the Desktop Window Manager, and new versions of system components built on the .NET Framework. After the 2003 "Summer of Worms", where three major viruses − Blaster, Sobig, and Welchia − exploited flaws in Windows operating systems within a short time period, Microsoft changed its development priorities, putting some of Longhorn's major development work on hold in order to develop new service packs for Windows XP and Windows Server 2003. Development of Longhorn was also "reset" in September 2004.