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VRRP cluster flapping when multiple VRRP clusters are connected to the same network segment
Symptoms
  • Status of VRRP clusters in the network is flapping - VRID status is constantly changing between Master and Backup.

  • Switch log shows messages regarding duplicate MAC addresses similar to this:
    %SW_MATM-4-MACFLAP_NOTIF: Host 0000.5e00.010a in vlan 5 is flapping between port Gi0/4 and port Gi0/1

Cause

VRRP VRIDs are configured in VRRP VMAC mode by default. VMAC Address has the following format (in Hex in internet standard bit-order):

00-00-5E-00-01-{VRID}

Since multiple VRRP clusters are connected to the same network segment, and by default each VRRP cluster starts counting the number of VRIDs configured from '1' and up, VRID on each VRRP cluster ends up with the same VMAC address. This will result in VRRP cluster flapping due to VRRP "Hello" packets being sent via Multicast.


Solution
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