Controller Based WLANs

This article applies to all the controllers running AOS version 6.3.0.0 or higher.

Two methods of Fast BSS transition can be used:

            a.Over-the-Air Fast BSS Transition
            b.Over-the-DS Fast BSS Transition

Aruba only supports “Over-the-air Fast BSS Transition method.

How does Over-the-air Fast BSS transition works

802.11r enabled Access Points advertise this capability in Beacon and Probe response frames by including a Mobility Domain Information Element (MDIE).

1. During the initial association in the mobility domain, an 802.11r capable STA and AP perform the 802.11 authentication, followed by a FT re-association exchange that differs from 802.11 re-association exchange by including an MDIE and FTIE (Fast Transition Information Element) in the re-association exchange. The FTIE carries the R0KH-ID (R0 Key Holder ID) as well as the current access point's R1KH-ID (R1 Key Holder ID).
2. After successful 802.11X authentication, the AP and STA engage in a Fast Transition (FT) four-way handshake that differs from the 802.11i handshake by carrying extra MDIE and FTIE components, needed for the derivation of PMK-R1s and PTKs.

The 802.11r amendment attempts to reduce latency by combining the 802.11 authentication and re-association frames with the 4-Way Handshake frames. So,the four key message frames are no more needed when the client roams, thus speeding up the roaming process.