If non-private v4 IP’s are assigned to domain computers without a global v6 address, it can cause strange issues for the DNS registrations and Active Directory functions. This issue occurs on new versions of Windows such as Windows 7+ and Server 2008+.
The short story is that the systems register a special 6to4 IPv6 address in the form 2002:abcd:1234::abcd:1234 as a AAAA (quad-A) record in DNS (the abcd:1234 is the hex form of the IPv4 address). Other systems will then prefer this special v6 address which is actually sent as IPv4 traffic by Windows (detects the special “2002” prefix address form and sends v4 traffic).
Suggestions include registering the corresponding 2002… prefixes in Active Directory sites and services, or disabling 6to4 with the Group Policy section Administrative Templates – Network – TCPIP Settings – Set 6to4 State.
Many thanks to Venkat Kalyanasundaram for writing the article “IPv6 for the Windows Administrator: The 2002: (6to4 Tunnel) Address and its Impact” and to Mark Morowczynski for sharing it on the Premier Field Engineer Platforms blog!