9.2 SSID

WLAN security, like other types of security, involves many layers of protection. Some of these layers are optional, but because of the inherent insecurity involved in WLANs it is a good idea to implement as many layers as possible.

The first layer of security is the Service Set Identifier (SSID), basically a password that has to be transmitted by the clients connecting to an access point. If the SSID sent by the client matches that enabled on the access point, a connection is established and communication can begin.

An SSID is also a good way to segment a wireless network. If a campus network is designed so that users should only have access to certain parts of the network, then different SSIDs can be used in different areas, restricting the access of users to certain parts of the network.

Table 9.2. Well-Known SSIDs

Manufacturer	Model	SSID
Cisco	BR1000	2 or tsunami
Compaq	WL-100	Compaq
DLink	DL-713	WLAN
INTEL	2011	Intel, xlan, or 101
SMC	SMC2652W	WLAN

SSID has several security problems associated with it, the biggest of which is that the default for most access points is to broadcast the SSID. Broadcasting the SSID obviously defeats the purpose of having it. Essentially, the access point is broadcasting its password to any devices with the same 802.11 standard enabled, defeating the purpose of having the SSID in the first place.

Even with SSID broadcast disabled on the access point, the SSID is still sent in plain text by the network device. If no encryption is enabled on the network, then an attacker with a WLAN scanning program will be able to sniff the password from devices configured to use it. Table 9-2 lists access point manufacturers and their well-known SSID.

Many network administrators do not change the SSID when a new access point is deployed, so the default SSID of the access point remains in place. As long as the same manufacturer makes the access point and WLAN Ethernet cards, the SSID will be the same for both, or the cards will be configured to accept a broadcast SSID.