seeing multiple mac address duplicated in Catalyst 6509 while the HSRP is not established

zulkarnain · ‎03-06-2021

Hi.

There is a symptom which one of vlan is having issue in HSRP. The log message start with this:

Mar 4 16:15:56.881: %HSRP-5-STATECHANGE: Vlan3 Grp 3 state Standby -> Active
Mar 4 16:16:02.405: %HSRP-5-STATECHANGE: Vlan3 Grp 3 state Active -> Speak
Mar 4 16:16:11.252: %MAC_MOVE-SP-4-NOTIF: Host 0000.0c07.ac03 in vlan 3 is flapping between port Router and port Po1

Then I found that the interface vlan 3 cannot ping each other from Core 1 & Core 2 vice-versa. The mac address for vlan 3 is having multiple duplicate mac address as I figure it out in Core 2. When doing show mac address-table for the specific mac address it shows coming from other port but when checked at the endpoint, it is not having the mention IP address. After I cleared the Core 2 mac address- table, then it learnt the correct mac address and IP. I just want to know what can be the root cause, and how to prevent it to happen in the future. Both Core Switch is using s72033-ipservicesk9-mz.122-33.SXH5.bin.

Thank You

Giuseppe Larosa · ‎03-07-2021

Hello @zulkarnain ,

a bridging loop in the affected VLAN is likely the root cause of your issue.

Investigate using

show spanning-tree vlan 3 detail

show spanning-tree vlan 3 detail | inc topology

You need to find out the ports that originate the toplogy changes and then you move to distribution/access layer switch connected to that port and repeat the above show command.

Hope to help

Giuseppe