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HSRP mac duplication erros causing vlans configured to flap

 
 
gurumurthy
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      02-14-2006
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

 
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J.Cottingim
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      02-14-2006
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

 
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Merv
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      02-14-2006

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

http://www.cisco.com/en/US/tech/tk64...80093f93.shtml

 
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gurumurthy
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      02-14-2006
Thanks for your responce Mr. Cottingim, all the interfaces got flapped
and all interfaces are in HSRP config.

 
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gurumurthy
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      02-14-2006
Thanks Mr. Merv, for your ref. WIll check and come back.

 
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J.Cottingim
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      02-14-2006
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.

 
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gurumurthy
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      02-14-2006
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

 
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