A DHCP workstation received an IP address conflict with mac address 78:2B:CB:4E:A6:6F. Through my switches, I tracked this MAC to a specific switch port. The switch says that port has 2 MAC addresses. The other one is 78:2B:CB:4E:A6:6D. The machine on this port is a Poweredge R510. It has 2 nics. One is disabled with no cable connected. The active NIC reports MAC address 78:2B:CB:4E:A6:6D and it has a static IP which is different from the IP in conflict. The disabled NIC in this machine has the mac 78:2B:CB:4E:A6:6E.
I rebooted the server. The mac address table on the switch dropped these 2 addresses. When the server booted back up, both mac addresses were back.
ipconfig /all only reports the correct static IP on the 6D mac address.
How does this NIC suddenly have 2 mac addresses and how does the second mac have an IP address assigned to it? It didn't get it from DHCP or it would have been recorded by the DHCP server. The IP doesn't respond to ping, http, telnet or ssh.