Two methods of secure roaming were introduced in 802.11i-2004: PMK Caching and Preauthentication. PMK caching is a method of roaming used in an RSN that speeds up a roam back to about 50ms ms on average. Let’s take a look at how that works. The clients and APs will maintain a cache of PMKs. Therefore, if a client wants to roam back to an AP that it has recently been associated with both the client and the AP will already have the PMK in thier cache so the 802.11X/EAP proces

The simplest form of roaming is reassociation. The client always makes the decision to roam based on proprietary criteria that are most often based on RSSI. Part 1 of this series on roaming, describes how reassociation occurs. Other types of roaming will be discussed later in this series. Once a client has decided that it wants to roam it send a reassociation request to the new AP. That AP sends an ACK. The new AP attempts to inform the original AP of the reassociation req