Fast Roaming
Users in a multi-AP network, especially with mobile devices, can move from one AP coverage area to another. But, the process of re-authentication can often take seconds to complete and this can impair wireless voice traffic and time sensitive applications. The FortiAP fast roaming feature solves this problem and is available only when moving between FortiAP units managed by the same FortiGate unit.
Fast roaming uses two standards-based techniques:
• Pairwise Master Key (PMK) Caching enables a RADIUS-authenticated user to roam away from an AP and then roam back without having to re-authenticate. To accomplish this, the FortiGate unit stores in a cache a master key negotiated with the first AP. This enables the 802.11i-specified method of “fast roam-back.”
• Pre-authentication or “fast-associate in advance” enables an 802.11 AP associated to a client to bridge to other APs over the wired network and pre-authenticate the client to the “next” AP to which the client might roam. This enables the PMK to be derived in advance of a roam and cached. When the client does roam, it will already have negotiated authentication in advance and will use its cached PMK to quickly associate to the next AP. This capability will ensure that wireless clients that support Pre-authentication to continue the data transfer without noticeable connection issues.