Windows 7 IPv6 fail

Sean Siler Sean.Siler at
Fri Oct 29 12:57:37 CEST 2010

Here is my translation:

You were trying to reach an IPv6 DST (resolvers) with no valid native v6 SRC, therefore Teredo was used to connect instead. Additionally, the RAs (I assume) were still present and configured your host for those v6 resolvers. Since they were still present, so were the resolvers. 


-----Original Message-----
From: at [ at] On Behalf Of Martin Millnert
Sent: Friday, October 29, 2010 5:39 AM
To: ipv6-ops at
Subject: Windows 7 IPv6 fail

Hi list,

I'm running Windows 7 on my home box dual-booted, so I had the luck to find a quite severe error (IMHO) in its IPv6 stack today:
   When (all?) IPv6 addresses on its wired interface becomes deprecated for whatever reason, it will still send out packets to the (wired) on-link router with Teredo source address.  (uhm, yeah, we were missing BCP38-style filters on the v6 router)

My Windows 7 network configuration is entirely vanilla, everything automatic from the network.

For a better description on what I found, please see the attached text-file.

So this is incorrect behaviour, for various reasons. In my case, our v6 resolvers that we hand out via stateless DHCPv6 (resolvers only), are being used for domain name look-up with a Teredo source address.
Reasonably, this is unsuccessful, since the source address isn't within the ISP allocated space, and the resolvers won't answer that.

Most web browsing worked fine, since there are 3 IPv4 resolvers to fall-back to.  But I stumbled on one name which the system failed entirely to look-up: I'm not sure how this came about; the v4 resolvers would answer this name, yet the system wouldn't give me an answer.
ping/browsing to failed.

A myriad of things could be 'fixed' / looked in to, IMO. For example:
 - Why query resolvers configured on the wired interface using an address configured on another interface?
 - Why send packets on the wired interface with a source address taken from another interface, in this case Teredo?
 - Why keep/use the v6 resolvers on the wired interface when addresses becomes deprecated, and wired IPv6 essentially drops? At least when resolvers aren't using link-local addresses?

MS clue greatly appreciated.

Martin Millnert <martin at>

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