The system detected an address conflict for IP address

Hi All,

I've a 2 node Windows Server 2012R2 Failover Cluster, quorum is on a network share. The cluster is up and running since some years.

I've performed a reboot of the passive node and the whole cluster went down, I'm investigating the issue. The first error I find is a failure of the cluster ip address itself:

"

The system detected an address conflict for IP address 172.16.20.69 with the system having network hardware address 00-50-56-B7-4E-50. Network operations on this system may be disrupted as a result.

"

this error has been logged on the passive node and the MAC address with conflicting IP is the MAC address of the public interface of the other node.