Windows 7 IPv6 fail

Martin Millnert martin at
Fri Oct 29 11:38:43 CEST 2010

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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