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Cluster instability when using ClusterXL with IGMP Snooping-enabled switches
Symptoms
  • When using a ClusterXL cluster with an IGMP Snooping-enabled switch, the user experiences cluster instability, e.g., one member will be in 'Down' state and the other will be in 'Active Attention' state. The state of the members may also be flapping.

  • When using a ClusterXL Load Sharing Multicast cluster with an IGMP Snooping-enabled switch, traffic will not go through the cluster.
Cause

When IGMP Snooping is enabled on the switch, it checks the Destination MAC Address of the frames in order to match the frames to IGMP Subscription Group. If IGMP membership is disabled on cluster members (i.e., fwha_enable_igmp_snooping=0), they never subscribe to IGMP Group on the switch. As a result, the switch cannot match the CCP packets that are sent to the Multicast MAC address to any IGMP Group and the switch drops these CCP packets. As a result, cluster members do not send or receive CCP packets properly. This triggers the cluster mechanism to assume that cluster members are failing and to declare interfaces as Down and/or to initiate a fail-over.

Note: IGMP Membership is enabled by default starting in R75.40 (i.e., fwha_enable_igmp_snooping=1).


Solution

Suggested solutions:

 

Refer to ClusterXL Administration Guide (R55, R60, R61, R62, R65, R70, R71, R75, R75.20, R75.40, R75.40VS, R76, R77) - Chapter 'High Availability and Load Sharing in ClusterXL' - Hardware Requirements, Compatibility and Cisco Example

 

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