Never been bitten by a SUP swap out but did have an issue with a chassis swap out. Was upgrading from a 6509 chassis to a 6509-VE chassis and was also running GLBP. Shut down the old 6K, racked the VE and put the blades in the same slot numbers and booted up with no issues. What we didn't realize is the base MAC addresses are based off the chassis, and when GLBP saw a different MAC it assumed this was AVF #3. There is a 4 hour GLBP AVF timer that removed AVF #1, leaving #2 and #3. Around 4 hours after the bootup our downstream WISMs stopped passing traffic. Their SVI were anchored on the 6K distribution and GLBP was used to handle first hop redundancy. Turned out the WISM has holding the old MAC address of the dead forwarder in memory and would not give it up, thus we were black holed. Could not clear ARP on the WLC and had to reboot the unit to resolve, and this reboot occurred after our downtime window because of the 4 hour AVF timer, and we had already gone home thinking mission accomplished,
Discovered WLC 6.x code did not handle GLBP properly and is corrected in 7.x. We had 9 more chassis to swap out and to avoid this issue, we would shut down the SVI on the chassis that was getting replaced 4 hours before the downtime, that way GLBP aged out the dead AVF gracefully and when we brought up the new VE chassis, everything worked OK and the WISM did not have any problems. We never saw any issues with PCs or any other devices, just the controllers running 6.x code.
