Networking

Six basic tips for implementing closed networking on a wireless network

Wireless networks must be closed off to outsiders--a difficult task considering that wireless networks are initially available to anyone within their range. These tips will help you protect your wireless network from unwanted users.


The purpose of properly securing a wireless access point is to close off the network from outsiders who do not have authorization to use your services. This is often easier said than done. A wireless network is more difficult to secure than a typical wired network because, while a wired network has a limited number of fixed physical points of access, a wireless network can be used at any point within the range of the antennas.

Despite the inherent difficulties, properly protecting your wireless networking system is key in safeguarding your system from serious security problems. If you deploy an insecure wireless network, it could result in a loss of service or in the use of your network as a launching pad for attacks against other networks. To help you close these security holes, make sure your networking staff follows these six quick wireless networking tips.

1. Plan antenna placement
The first step in implementing a closed wireless access point is to place the access point’s antenna in such a way that it limits how far the signal can reach beyond the coverage area. Don’t place the antenna near a window, as the glass does not block the signal. Ideally, your antenna will be placed in the center of the area you want covered, with as little signal leaking outside the walls as possible. Of course, it’s next to impossible to completely control this, so other measures need to be taken as well.

2. Use WEP
Wired equivalent privacy (WEP) is a standard method for encrypting traffic over a wireless network. While it has major weaknesses, it is useful in deterring casual hackers. Many wireless access point vendors ship their units with WEP disabled in order to make the product installation easier. This practice gives hackers immediate access to the traffic on a wireless network as soon as it goes into production, since the data is directly readable with a wireless sniffer.

3. Change the SSID and disable its broadcast
The service set identifier (SSID) is the identification string used by the wireless access point by which clients are able to initiate connections. This identifier is set by the manufacturer, and each one uses a default phrase, such as “101” for 3Com devices. Hackers who know these pass phrases can easily make unauthorized use of your wireless services. For each wireless access point you deploy, choose a unique and difficult-to-guess SSID, and, if possible, suppress the broadcast of this identifier out over the antenna so that your network is not broadcast for use. It will still be usable, but it won’t show up in a list of available networks.

4. Disable DHCP
At first, this may sound like a strange security tactic, but for wireless networks, it makes sense. With this step, hackers would be forced to decipher your IP address, subnet mask, and other required TCP/IP parameters. If a hacker is able to make use of your access point for whatever reason, he or she will still need to figure out your IP addressing as well.

5. Disable or modify SNMP settings
If your access point supports SNMP, either disable it or change both the public and private community strings. If you don’t take this step, hackers can use SNMP to gain important information about your network.

6. Use access lists
To further lock down your wireless network, implement an access list, if possible. Not all wireless access points support this feature, but if yours does, it will allow you to specify exactly what machines are allowed to connect to your access point. The access points that support this feature can sometimes use trivial file transfer protocol (TFTP) to periodically download updated lists in order to prevent the administrative nightmare of having to sync these lists on every unit.

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