Closed Network

Another popular authentication feature of wireless the so-called closed network. In a typical network, APs will broadcast their ESSID many times per second, allowing wireless clients (as well as tools such as NetStumbler) to find the network and display its presence to the user. In a closed network, the AP does not beacon the ESSID, and users must know the full name of the network before the AP will allow association. This prevents casual users from discovering the network and selecting it in their wireless client.

There are a number of drawbacks to this feature. Forcing users to type in the full ESSID before connecting to the network is error prone and often leads to support calls and complaints. Since the network isn't obviously present in site survey tools like NetStumbler, this can prevent your networks from showing up on war driving maps. But it also means that other network builders cannot easily find your network either, and specifically won't know that you are already using a given channel. A conscientious neighbor may perform a site survey, see no nearby networks, and install their own network on the same channel you are using. This will cause interference problems for both you and your neighbor.

Finally, using closed networks ultimately adds little to your overall networks security. By using passive monitoring tools (such as Kismet), a skilled user can detect frames sent from your legitimate clients to the AP. These frames necessarily contain the network name. A malicious user can then use this name to associate to the access point, just like a normal user would.