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ClusterXL forwarding of ARP Reply packets might cause duplicate entries on a Cisco Load Balancer Technical Level
  • By default, all ARP Reply packets received by the Active cluster member are forwarded to other peer members. This behavior may cause connectivity issues on some Layer-3 devices connected to the cluster. These ARP packets are re-broadcasted or multicasted from the Active Member.

  • For example, on Cisco ACE Load Balancer:

    1. ARP Request is sent from the Standby cluster member to some external server
    2. External server sends an ARP Reply received from physical port X on the Load Balancer
    3. The Active cluster member receives the ARP Reply packet and forwards it to the Standby cluster member (with exactly the same payload)
    4. The Load Balancer receives this identical forwarded ARP Reply packet on physical port Y, which causes it to alert on conflict with port X
  • Note - This issue has been seen on Nexus 7k switches
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