HSRP mac duplication erros causing vlans configured to flap

The duplicate IP address error your speaking of is caused by the standby router taking over the HSRP address and starts replying the ARP requests, forwarding packets, etc.

This is normally caused by momentary loss of communication between the two routers.

Things to look for (off the top of my head) * Misconfigured duplex on the link(s) between the two routers. - both sides of each link must match exactly (full full, auto auto, etc.)

• High CPU utilization on either router - many neighbor relationships in your routing protocol. Consider using passive interfaces for "access" vlans. One neighbor relationship between the two routers is enough to update their tables. - spanning-Tree loops / recalculations - large STP topology

Did ALL of your interfaces experience the "flap"? Also, how many interfaces do you have configured with HSRP?

J.Cottingim

Suggest you have a look at Cisco docs on HSRP instability in a switch environment:

Thanks for your responce Mr. Cottingim, all the interfaces got flapped and all interfaces are in HSRP config.

Thanks Mr. Merv, for your ref. WIll check and come back.

Are you monitoring link utilization? - check for high link utilization during that time. Also, do you have syslog configured? - if you do try to find anyting that's not "normal" at the time of the flap.

I fear that i have not made my question clear initially, this router is a MSFC routing processor used for intervlan routing.

Also i have checked the syslogs and from that only got this HSRP mac duplication message and the consequent vlan flaps.

Regards Gurumurthy