Common Wireless Networking Terms
Learning the ins and outs of wireless Linux networks will be easier if we're all speaking the same language. Before proceeding, take time to become familiar with three key wireless terms: wireless access point, Service Set ID, and shared encryption key. Learn them now, because you'll see them throughout the chapter.
Wireless Access Points
A wireless access point (WAP) is a device that acts as the central hub of all wireless data communications. In the most common operating mode (Infrastructure mode), all wireless servers communicate with one another via the WAP, which is usually connected to a regular external or integrated router for communication to the Internet. WAPs are, therefore, analogous to switches in regular wired networks.
Servers can communicate with one another without a WAP if their NICs are configured in Ad Hoc mode, but this prevents them from communicating with any other communications path. For that, you need a WAP on your network.
Extended Service Set ID
The 802.11a/b wireless networks typically found in a home environment share the same frequency range with one another so it is possible for your computer to hear the traffic meant for somebody else's nearby network. The Extended Service Set ID (ESSID) helps prevent the garbling of messages. Each wireless network needs to be assigned an ESSID that doesn't match that of any neighboring networks within its range of operation. The desired ESSID is then set on both wireless NICs and WAPs, which in turn ignore all traffic using other identifiers.
Most wireless software packages enable you to view all the available ESSIDs within range and give you the option of selecting the corresponding wireless LAN (WLAN) to join. Unfortunately, this makes it easy to eavesdrop on a neighboring network, and therefore it is best to not only change your ESSID from the factory defaults, but also to encrypt your wireless data whenever possible.
The term ESSID is frequently interchangeably referred to as a Service Set ID (SSID) by many vendors. I'll stick with ESSID unless the term SSID is relevant to an application.
Encryption Keys
Encryption is a method of encoding data so that only people with the secret key to unlock the code can view the original data. As expected, if you encrypt your wireless network's data then you also need to use a shared encryption key on all the NICs and WAPs. Some software packages allow you to use a plain text key, but the more secure ones treat the key like a password and prompt you to enter your chosen key twice without your actually being able to ever see the unencrypted key again.
It is always best to encrypt your network data last to simplify troubleshooting. Make sure everything works normally first and then encrypt later.
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