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HSRP mac duplication erros causing vlans configured to flap

Hi group,

I have got a problem in my network relating to HSRP mac duplication & expecting some soultion from this group.

Scenario is two routers are configured for HSRP, which are the routing processors of catalyst L3 swiches, one router in active and other in standby. Many vlans are configured in both the switches for buisness, and is extended to the routing process. The problem is suddenly the virtual HSRP mac got a ip duplication from active HSRP router.

Becoz of which the vlans in standby router got changed its state from standby to active, flapped for few minutes and went back to normal. No configuration changes were done in any routers or switches at that time or even before.

No logs were found for the error and the only log got is this mac duplication.

Can anyone have come across the similar case, pls share with me.

Thanks in advance.

Gurumurthy

Reply to
gurumurthy
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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

Reply to
J.Cottingim

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

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Reply to
Merv

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

Reply to
gurumurthy

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

Reply to
gurumurthy

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.

Reply to
J.Cottingim

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

Reply to
gurumurthy

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