Networking optimize

The two stages in securing Linksys wireless networks

A list of simple Linksys security fixes

By default, many wireless devices can leave networks and data open to access, paving the way for practices like war driving, in which someone armed with a wireless network card and a few easily-obtainable hacker tools, can identify a wireless network and connect to it to access company data.

As network consultants, our mission is to provide the convenience of wireless networks in a relatively secure environment. To help you in this effort, here is a list of simple security fixes that will provide additional protection when you’re installing a Linksys wireless network access point for your clients.

Equipment used
The options I describe in this article will be based on use of:
  • A Linksys wireless network access point; this device provides access for wireless clients to the wireless network.
  • Linksys USB and PCMCIA network adapters for clients.
  • A Windows XP operating system.

Stage one: Security configurations for the wireless network access point
In this first stage, you should make sure that the wireless network is running and clients are able to connect. You should note that some of the security configurations that I list here will make it more difficult to isolate network connectivity problems. But, ultimately, the enhanced security is worth the extra connectivity troubleshooting you might have to do down the road.

The configurations for stage one are:
  1. Place wireless access point away from windows or exterior walls. The closer an access point is to a window or exterior wall the greater the signal will be outside the building.
  2. Change the default settings for the access point. In particular, you should change the default IP address, the default service set identifier (SSID), and the default administrative password. To do so, access the Web-based administration utility on the access point, and then make appropriate changes to the Setup and Password pages. Figure A below shows what you’ll see, for example, on the Setup page.
    Choose combinations that are complex for the SSID and password, which include letters, numbers, and special characters. The phrases should be at least nine characters long. Although this sounds like basic information, all too many businesses have neglected to perform this simple task and have found their networks compromised because of this oversight.
  3. Enable logging. The log tells you which computers (by MAC address) have connected to the network. As with any log, you should do a quick scan on a daily basis to see if there is any unusual activity. To change the log, open the Log Web page within the administration utility. Figure B shows you what this screen looks like.

Figure A


Figure B

You can also have the log sent to another computer and view it using the Log Viewer utility provided by Linksys. I prefer this method because I can centralize my log files. Unfortunately, the Log Viewer is only available by sending an e-mail to Linksys Web site’s support desk.

Once you have completed these configurations, make sure all clients can connect successfully. You also should see what type of information is normally accessible by wireless network analyzers. A simple, free tool for this task is NetStumbler. Figure C highlights information accessible on a wireless network using NetStumbler.

Figure C

Notice that NetStumbler identifies the access point, its maker, and the SSID. With this type of information, a person can connect to your wireless network. Therefore, it’s now time to talk about how to reduce the likelihood that others will discover information about your network, connect to the network, and pull data from it.

Stage two: Security configurations
There are several methods for enhancing security on a wireless network, including the following:

Enable MAC filtering
With this method, you list the network adapters that are allowed to connect to the network by MAC address. The MAC address on a Linksys wireless network adapter is located on the bottom of the device. You can also get the MAC address by typing the commandipconfig /all (WINDOWS NT/2000/XP) at the command prompt while the wireless network adapter is installed on the computer.

The MAC address is listed as the Physical Address with this command. Once you have the MAC addresses, you can enable MAC filtering and list MAC addresses for clients you want to connect to the network. To access this page, you have to go to the Advanced tab in the Web-based administration utility for the access point (see Figure D).

Figure D

Enable wired equivalent protocol (WEP)
This method keeps outsiders from viewing data transmitted on your wireless network. Although WEP has come under fire because the protocol can be hacked, understand that your network is still more secure with WEP than without. The key is to change the WEP encryption key regularly. I recommend doing it once a week, but many of you will feel this is too much work.

My advice is to balance the need for security with the administrative load. For those of you who are comfortable with scripting, you can create a script that will change the WEP passphrase (upon which the encryption keys are generated) and automatically update clients. More expensive wireless network equipment may have features built-in to do this. To set these features, you will use the Setup page to make WEP mandatory. Then use the WEP Setting page to generate the encryption keys in the Web-based administration utility for the access point.

Set encryption for 128-bit encryption. The higher the encryption, the more difficult it is to compromise it. Some wireless network devices provide 256-bit encryption as well, but both the access point and client network adapters need to support it.

Disable SSID broadcasting
Without the SSID being broadcast, your network is more difficult to locate. To set this option, go to the Wireless page under the Advanced tab in the Web-based administration utility for the access and choose Disable in the SSID Broadcast field (see Figure E).

Figure E

Final check
After having done all of this, you can run NetStumbler again to see what type of information is accessible. You should find that none of your wireless network devices are located. Note that when WEP is enabled and SSID broadcasting remains enabled, the access point—including the MAC address—will still be visible; however, the name of the SSID will not appear.