Something similar has occured to me and it's giving me a big headache. In a nutshell the culprit is the DHCPRELEASE message generated by a client when it disassociates from an accesspoint or the client shuts down. When this happens the DHCP on the BBSM removes the lease causing the client to get a different IP next time it associates to the network. The problem is that this may happen in a shorter time than the porthop delay causing a stale session for that user. Is there a solution to this problem from Cisco?
