From what I remember reading, I think the short answer is "you can't" Vista and Server 2008 default to IPv6 first, but XP and server 2003 default to IPv4 first. I have seen some people mention that FireFox will try and connect first over IPv6 even on XP, but I'm not sure how true that is.

http://technet.microsoft.com/en-us/library/bb877985.aspx has detailed information on source and destination address selection methodologies for Windows. I no longer host my tunnel from XP (using a linux variant at the moment with radvd), so can't readily check that case, but my XP SP3 machine always prefers a global unicast IPv6 address to IPv4 when both a A and AAAA record exist (and are returned) for a given dns name query. (i.e. www.kame.net) This is true for telnet, iexplore, firefox, putty, and I expect most properly written IPv6 aware applications. (unless specifically written with unique address selection criteria) It is possibly that a tunnel hosted on an XP box gives a different policy to address selection, but that should be able to be seen from netsh. My XPSP3 default precedence table: Querying active state... If you need more MS IPv6 info, google "ipv6 site:microsoft.com", as there are quite a few good articles and docs available. Like the MS IPv6 FAQ http://technet.microsoft.com/en-us/network/cc987595.aspx Good Luck. -_Dave