Just ran into a little something I have not seen in a long time. Building edge servers with Windows Server 2012R2 and the external NIC kept coming up as duplicate address. Doing all the cross checking showed that the server had only two interfaces and that they were configured properly. Turns out that this little gem from 2008 R2 days is still valid:
The firewall doing the NAT to the public IP was ASA. The registry change for disabling gratuitous ARP fixed all of the my edges.
This might be of interest also: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1028373