Linksys WRT51AB Router Manual PDF (Setup & Configuration Guide)

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Dual-Band Wireless A+B Broadband Router

I have excellent signal strength, but I cannot see my network.

WEP is probably enabled on the Router, but not on your wireless adapter (or

vice versa).

Verify that the same WEP keys and levels (64, 128, or 152) are

being used on all nodes of your wireless network.

How many channels/frequencies are available with the Router?

Using 802.11a, there are eight available channels, ranging from 36 to 64.

Using 802.11b, there are eleven available channels, ranging from 1 to 11.

What is Turbo Mode?

Turbo Mode allows high-speed connections, but severely limits range.

work, Turbo Mode must be enabled on both the Router and the wireless PCs.

Turbo Mode is not compatible with Windows XP and may only function with

Linksys 5GHz wireless adapters.

What is the difference in range between 802.11a and 802.11b products?

Overall, range will be a little less in a typical environment, and while higher

speeds may be achieved with 802.11a, throughput degrades more quickly. (See

Figure A-1.)

If your questions are not addressed here, refer to the Linksys website,

www.linksys.com

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What is WEP?

WEP is Wired Equivalent Privacy, a data privacy mechanism based on a 64-bit

or 128-bit shared key algorithm, as described in the IEEE 802.11 standard.

What is a MAC Address?

The Media Access Control (MAC) address is a unique number assigned by the

manufacturer to any Ethernet networking device, such as a network adapter,

that allows the network to identify it at the hardware level. For all practical pur-

poses, this number is usually permanent. Unlike IP addresses, which can

change every time a computer logs onto the network, the MAC address of a

device stays the same, making it a valuable identifier for the network.

How do I avoid interference?

If you are using the Router and one or more Access Points in close proximity

to one another, and they are set on the same channel, interference will be gen-

erated. To avoid interference, be sure to set the Router and all Access Points to

different channels (frequencies); in other words, assign a unique channel to the

Router and each Access Point.

How do I reset the Router?

Press the

Reset

button on the back panel for about ten seconds. This will reset

the Router to its default settings.

How do I resolve issues with signal loss?

There is no way to know the exact range of your wireless network without test-

ing. Every obstacle placed between the Router and a wireless PC will create

signal loss.

Lead glass, metal, concrete floors, water and walls will inhibit the

signal and reduce range.

Start with the Router and your wireless PC in the

same room and move it away in small increments to determine the maximum

range in your environment.

You may also try using different channels, as this may eliminate

interference

affecting only one channel. Also, due to FCC regulations, more power may be

transmitted, using 802.11a, on channels 52, 56, 60 and 64, than on the lower

channels.

Lastly, click the

Advanced

tab of the web-based utility and make

sure that FULL is selected in the

Transmission Power

field.

Does the Turbo Mode work with Windows XP PCs?

No. The Turbo Mode does not work with Windows XP PCs.

Figure A-1

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Step One: Pinging an IP Address

The first step to determining your ISP’s web and e-mail server address is to

ping its IP address.

Power on the computer and the cable or DSL modem, and restore the net-

work configuration set by your ISP if you have since changed it.

2. Click

Start

and then

Run

. Type

command

in the

Open

field. This will

bring up the DOS window.

At the DOS command prompt, type

ping mail

(assuming that the location

for which you’re trying to find an IP address is configured as

mail

). Press

the

Enter

key. Information such as the following data, taken from a ping of

Microsoft Network’s e-mail server, will be displayed.

C:\>ping mail

Pinging mail [24.53.32.4] with 32 bytes of data:

Reply from 24.53.32.4: bytes=32 time<10ms TTL=128

Ping statistics for 24.53.32.4:

Packets: Sent = 4, Received = 4, Lost = 0 (0%

loss),

Approximate round trip times in milli-seconds:

Minimum = 0ms, Maximum =

0ms, Average =

0ms

Write down the IP address returned by the ping command (in the example

above: 24.53.32.4.). This IP address is the actual IP address of the server

mail

, or any other word or value you have pinged.

Figure B-1

Appendix B: How to Ping Your

ISP’s E-mail & Web Addresses

Virtually all Internet addresses are configured with words or characters (e.g.,

www.linksys.com

www.yahoo.com

, etc.) In actuality, however, these Internet

addresses are assigned to IP addresses, which are the true addresses on the

Internet. For example, www.yahoo.com is 66.218.71.87 (this IP address may

change). Type it into your web browser and you will wind up at the Linksys

home page every time. There are servers that translate the URL to an IP

address; this is called the Domain Name System (DNS).

IP and web addresses, however, can sometimes be long and hard to remember.

Because of this, certain ISPs will shorten their server addresses to single words

or codes on their users’ web browser or e-mail configurations. If your ISP’s e-

mail and web server addresses are configured with single words (

www

e-mail

home

pop3

, etc.) rather than whole Internet addresses or IP addresses, the

Router may have problems sending or receiving mail and accessing the

Internet. This happens because the Router has not been configured by your ISP

to accept their abbreviated server addresses.

The solution is to determine the true web addresses behind your ISPs code

words. You can determine the IP and web addresses of your ISP’s servers by

“pinging” them.

Important

: If you don’t have your ISP’s web and e-mail IP

addresses, you

must

either get them from your ISP or follow these

steps

prior

to connecting the Router to your network.

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Appendix C: Configuring

Wireless Security

The Router offers two wireless security features. The basic feature is Wired

Equivalent Privacy (WEP) encryption, an encryption method used to protect

your wireless data communications. WEP uses 64-bit, 128-bit, or 152-bit keys

to provide access control to your network and encryption security for every

data transmission. To decode a data transmission, each point in a network must

use an identical key. Higher encryption levels mean higher levels of security,

but due to the complexity of the encryption, they may mean decreased network

performance.

You may also have heard the term “40-bit” used in conjunction with WEP

encryption. This is simply another term for 64-bit WEP encryption.

This level

of WEP encryption has been called 40-bit because it uses a 40-bit secret key

along with a 24-bit Initialization Vector (40 + 24 = 64). Wireless vendors may

use either name. Linksys uses the term “64-bit” when referring to this level of

encryption.

The second wireless security feature is 802.1x. The IEEE 802.1x standard spec-

ifies authentication methods for a wireless client, such as a PC, to access a net-

work, so network security is enhanced. Based on the Extensible Authentication

Protocol (EAP), 802.1x designates how a client accesses a network server, fre-

quently a RADIUS server, with the Router acting as an authenticator. When a

network uses 802.1x, the identity of the client is verified before the client is

allowed network access.

For example, a wireless user may use one of the authentication methods to

access a wireless network protected by an authentication server. The user’s PC

sends a request to the Router (an access point can be used instead). The Router

sends an identification request back to the PC. After the PC sends the Router the

identification message, the Router forwards the identification message to the

server. If the server accepts the identification message, then the PC is permitted

access to the wireless network.

Background

Note:

WEP encryption is an additional data security measure and not

essential for router operation; however, Linksys recommends the use

of WEP encryption.

Step Two: Pinging for a Web Address

While the IP address returned above would work as your e-mail server address,

it may not be permanent. IP addresses change all the time. Web addresses, how-

ever, usually don’t. Because of this, you’re likely to have fewer problems by

configuring your system with web addresses rather than IP addresses. Follow

the instructions below to find the web address assigned to the IP address you

just pinged.

At the DOS command prompt, type

ping -a 24.53.32.4

, where 24.53.32.4

is the IP address you just pinged. Information such as the following data

will be displayed.

C:\>ping -a 24.53.32.4

Pinging mail.msnv3.occa.home.com [24.53.32.4] with

32 bytes of data:

Reply from 24.53.32.4: bytes=32 time<10ms TTL=127

Ping statistics for 24.53.32.4:

Packets: Sent = 4, Received = 4, Lost = 0 (0%

loss),

Approximate round trip times in milli-seconds:

Minimum = 0ms, Maximum =

0ms, Average =

0ms

Write down the web address returned by the ping command. (In the exam-

ple in Figure C-2,

mail.msnv3.occa.home.com

is the web address.) This

web address is the web address assigned to the IP address you just pinged.

While the IP address of

mail

could conceivably change, it is likely that this

web address will not.

Replace your ISP’s abbreviated server address with this extended web

address in the corresponding Internet application (web browser, e-mail

application, etc.).

Once you have replaced the brief server address with the true server address,

the Router should have no problem accessing the Internet through that Internet

application.

Figure B-2

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Dual-Band Wireless A+B Broadband Router

In addition to enabling WEP, Linksys also recommends the following security

implementations:

•

Change the SSID from the default “linksys”

•

Change the SSID on a regular basis

•

Change the WEP key regularly

•

Enable MAC address filtering (if your wireless products allow it)

For instructions on how to configure the Router’s WEP settings, go to the

“Setup” section of “Chapter 6: The Router’s Web-Based Utility.” For instruc-

tions on how to configure the WEP settings of your PC’s wireless adapter, refer

to your wireless adapter’s documentation.

Many authentication methods, including passwords, certificates, and smart

cards (plastic cards that hold data), work within the 802.1x framework. The

Router supports two authentication types: MD5 and certificate-based (TLS or

TTLS).

MD5 authentication is a type of one-way authentication method that employs

user names and passwords. TLS and TTLS authentication are two-way authen-

tication methods that employ digital certificates to verify the identity of a

client. TLS, or EAP-TLS, exclusively uses digital certificates, while TTLS, or

EAP-TTLS, uses a combination of certificates and another method, such as

passwords, for authentication. MD5 authentication is not as secure as either

certificate-based authentication method, and TLS is more secure than TTLS

authentication.

To use 802.1x authentication, you have to enable the 802.1x feature on the

Router as well as your wireless-equipped PCs. For instructions on how to con-

figure the Router’s 802.1x settings, go to the “Advanced Wireless” section of

“Chapter 6: The Router’s Web-Based Utility.”

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Important:

The Router’s 802.1x feature works with Windows XP.

It may also work with other Windows operating systems, depend-

ing on the specifics of your PC’s operating system and the 802.1x

client software being used.

802.1x Authentication

Important:

The Router’s 802.1x feature works with a RADIUS

server. It may also work with other types of authentication servers,

depending on the specifics of each authentication server.

There are two types of WEP encryption for 802.1x, static and dynamic. Static

WEP keys are more vulnerable and can only be changed manually on all

devices, including the Router. If you are using MD5 authentication, then you

can only use static WEP keys. Dynamic WEP keys are keys that are renewed

automatically on a periodic basis. This makes the WEP key(s) more difficult to

break, so network security is strengthened. To enable dynamic WEP keys, you

must use 802.1x certificate-based authentication methods, such as TLS or

TTLS.

Make sure your wireless network is functioning before attempting to configure

WEP encryption.

On a wireless network, a 128-bit WEP encrypted device will NOT communi-

cate with a 64-bit WEP encrypted device. Therefore, make sure that all of the

wireless devices on each network are using the same encryption level.

Note:

802.1x is an advanced data security measure and not essential

for router operation. It will, however, increase network security.

Note:

If you are roaming between access points, you will have to go

through the 802.1x authentication procedure each time your computer

connects to a new access point.

Figure C-1

Cable or DSL Modem

Router

RADIUS Server

Notebook with

Wireless Adapter

Notebook with

Wireless Adapter

WEP Encryption

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The screen that appears will show any available wireless network. Select the

appropriate network, and click the

Advanced...

button.

3. Click the

Authentication

tab. Make sure the box next to

Enable network

access control using IEEE 802.1X

is checked. In the drop-down box next

EAP type

, select

MD5-Challenge

. Make sure the box next to

Authenticate as computer when computer information is available

checked. Then click the

button.

Figure C-4

Figure C-3

Windows XP supports 802.1x with MD5 or TLS authentication. In this appen-

dix, the following sections will discuss 802.1x configuration for PCs running

Windows XP. If you are using MD5 authentication, proceed to “MD5

Authentication for Windows XP.” If you are using TLS authentication, go to the

appropriate section, “Digital Certificate Installation” or “TLS Authentication

for Windows XP,” depending on whether or not you have already installed a

digital certificate on your PC.

If your PC is not running Windows XP, then your PC must use third-party

802.1x client software. For instructions on how to configure 802.1x through

third-party software, refer to that application’s documentation.

Make sure you have installed the wireless adapter correctly into your PC.

Click the

Wireless Network Connection

icon located in your computer’s

system tray.

MD5 Authentication for Windows XP

Important:

Make sure you have the User name, Password, Logon

domain (if applicable), and WEP key needed to access the appropriate

wireless network. If you need any of this information, contact your net-

work administrator beforehand.

Figure C-2

Note:

These are the instructions and screenshots for Windows XP

without Service Pack 1 installed. If you have already installed

Service Pack 1, enter the keyword

802.1x

in the Windows XP search

engine for your 802.1x setup instructions.

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