We've been having an issue for the last few weeks on a relatively small network. The issue started when we swapped a specific Cisco 3750 for a 2960G (there were some other changes), exactly since then we now get the following notifications all day long:
019534: Feb 27 01:28:39: %SW_MATM-4-MACFLAP_NOTIF: Host 0016.3e64.98e2 in vlan 100 is flapping between port Gi0/22 and port Gi0/24
We get this on multiple mac addresses and multiple vlans, the above is the most common one we see (there are thousands per day).
The mac address in question is for a VM on a server, obviously the server does not move and is physically located on another switch directly connected to Gi0/24. Gi0/22 is the uplink to the central router (there are other switches upstream, non if which are logging flaps), so the questions follows - how is this switch learning the VM's mac on Gi0/22 ?
Obviously the first thing was to eliminate a L2 loop, we have looked into this many times, rebuilding diagrams from scratch using both cdp and physical tracing and we absolutely cannot find a loop anywhere. Additionally, STP is not reporting any blocked paths, confirming that no loop has been detected.
Any help or tips on how to debug this would be greatly appreciated.