HSRP mac duplication erros causing vlans configured to flap

Discussion in 'Cisco' started by gurumurthy, Feb 14, 2006.

  1. gurumurthy

    gurumurthy Guest

    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

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

    Thanks in advance.

    gurumurthy, Feb 14, 2006
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  2. gurumurthy

    J.Cottingim Guest

    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, Feb 14, 2006
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  3. gurumurthy

    Merv Guest

    Merv, Feb 14, 2006
  4. gurumurthy

    gurumurthy Guest

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

    gurumurthy Guest

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

    J.Cottingim Guest

    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.
    J.Cottingim, Feb 14, 2006
  7. gurumurthy

    gurumurthy Guest

    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.

    gurumurthy, Feb 14, 2006
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