ClusterXL HA Failover Stalls After Data Center Fabric Refresh
A pair of R81.10 16200 appliances runs ClusterXL HA for a 4,000-user campus. Each appliance connects to a Cisco Nexus pair with two 25GbE ports in an LACP bond; the cluster sync network is a separate 10GbE bond on VLAN 100. CCP uses the default multicast mode. After the fabric team enabled IGMP snooping on VLAN 100 and changed the LACP hash to layer3+4, a manual clusterXL_admin down takes 42 seconds to fail over. cphaprob stat briefly shows both members active; cphaprob -a if alternates between UP and DOWN on the sync bond. SecureXL is enabled, and there is no maintenance window: the pair must stay in HA during the fix. The trading floor VLAN 30 cannot tolerate more than two seconds of packet loss during a controlled failover.
1. The fabric change is the only recent change. What is the most likely failure mechanism, and which three checks would confirm it before you touch the cluster?
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The most likely mechanism is that IGMP snooping on VLAN 100 is dropping the ClusterXL CCP multicast hellos. ClusterXL HA depends on continuous CCP exchange between members. If the standby stops receiving hellos, it can conclude the active is gone and promote itself; if the original active is still healthy, both members may briefly claim active, and normal state synchronization does not complete until CCP is re-established. That produces the 42-second stall and the alternating sync-interface state.
Three checks:
- Run
cphaprob -a ifandcphaprob staton both members. A sync bond that flaps between UP and DOWN while the physical member links are up points to control-plane loss, not cabling. - Capture on VLAN 100 on both sides with
tcpdump -ni <sync_if> host 224.0.0.184 or port 8116. If hellos are sent but not received, the switch is dropping multicast. - Check the Nexus VLAN 100 configuration for IGMP snooping without a querier, and confirm whether a multicast router port exists. Also verify the LACP hash change did not create a single-member bond; asymmetric hashing is a secondary suspect, but a 42-second CCP loss is not explained by hashing alone.
2. How would you restore fast failover without disabling SecureXL or taking the cluster out of HA?
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First fix the control-plane path, not SecureXL. Two viable fixes are:
- Enable an IGMP querier on VLAN 100 or configure a proper multicast router port so CCP hellos are flooded to both members.
- If the fabric team will not support multicast, change ClusterXL CCP to unicast. In R81.10, apply
cphaconf set_ccp unicaston the standby first, verifycphaprob -a ifandcphaprob stat, then perform a controlled failover and apply the same setting to the former active. This keeps HA and does not disable SecureXL.
Also correct the sync bond: confirm both 10GbE members are up, the LACP bond is not in a single-member state, and the sync VLAN is allowed on both sides. Keep interface monitoring enabled for the sync bond but do not monitor the LACP member ports individually if that would cause unnecessary failovers. Test with clusterXL_admin down during a low-risk window and measure failover time. A correct result is under three seconds for VLAN 30, not merely a stable cphaprob display.
3. What verification and rollback criteria would you set before declaring the issue closed?
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Verification should prove three things: CCP is stable, state sync is complete, and failover actually meets the two-second requirement.
Use cphaprob stat, cphaprob syncstat, and cphaprob -a if repeatedly for at least 30 minutes. Capture CCP traffic again and confirm hellos are received on both members. Run a controlled failover with a continuous ping and a TCP transaction on VLAN 30; record the actual outage. Check fw ctl pstat and cluster logs for sync queue growth or 'CCP packet dropped' messages.
Rollback criteria: if unicast CCP causes any member to lose sync or if failover exceeds two seconds after two controlled tests, revert to the previous CCP mode during the same window and pursue the IGMP querier fix instead. Do not leave the cluster in a state where both members can become active. Keep the old fabric configuration documented so the switch change can be reverted independently.