A WLAN consists of Wireless Access Points as discussed in Chapter 2, Networks for Digital Enterprises. These access points (APs) provide the layer 1 and layer 2 functionality of the OSI stack. An AP is a self-sufficient layer 2 device that provides connectivity back to the network. The upstream connectivity from the AP is generally through an Ethernet port on the AP. Sometimes, the APs are used in a mesh mode or as repeaters and the uplink connectivity might also be through a wireless medium. We will consider the APs connected directly to a switch port, which is the most common form of enterprise deployment in this book.

All 802.11 WLANs use a service set identifier, abbreviated as SSID, which is a unique identifier that the wireless clients use to identify and join networks. APs can broadcast this SSID so that it is visible to other users. Some SSIDs might...