This was a particularly odd issue which I had never experienced before so I thought it’s worth blogging about it.
During a normal MS Failover Cluster failover operation, the node calming the cluster roles sends out a GARP request to notify the networking infrastructure of the MAC address change. The Layer 3 switch / router then updates the MAC address in the ARP table and packets are routed to the node which claimed the cluster roles. Recently I found myself troubleshooting a MS Failover cluster deployment which wasn’t behaving quite in this manner.
Some background info:
- For the sake of this blog post lets call the 2 nodes A and B.
- The nodes are running Server 2016, SQL 2012 and Microsoft Failover Cluster services.
- Each node has 2 NICs, one for the client and management network, and one for the heartbeat network.
- The cluster consists of 3 Network resource; a cluster IP address and 2 SQL instance addresses which float between the 2 nodes depending on which one is active.
- All 3 IP addresses are in the same VLAN.
- Running continues ping to all 3 IP addresses during failover tests.