Yesterday's Windows update causes IPv4 to be default

Dan Wing dwing at
Wed Nov 14 23:20:57 CET 2012

> -----Original Message-----
> From: Mike Jones [mailto:mike at]
> Sent: Wednesday, November 14, 2012 12:12 PM
> To: Tassos Chatzithomaoglou
> Cc: Dan Wing; ipv6-ops at
> Subject: Re: Yesterday's Windows update causes IPv4 to be default
> On 14 November 2012 19:16, Tassos Chatzithomaoglou
> <achatz at> wrote:
> > If this is MS's new way of doing HE, then i'm little bit worried about
> > choosing a protocol based solely on connectivity to an external
> entity.
> The only real detail I could find about this testing was the following:
> windows-8.aspx
> Windows 8 performs the network connectivity test when you first connect
> to a new network; it caches this information and repeats the test every
> 30 days. The actual test for connectivity is a simple HTTP GET to an
> IPv6-only server that is hosted by Microsoft. (For standards buffs, this
> is implemented between rules 5 and 6 of destination address sorting in
> our implementation of RFC 3484.) Windows performs a similar network
> connectivity test for IPv4 connectivity. If both IPv4 and IPv6 are
> functioning, IPv6 will be preferred.
> Anyone know of a more detailed write-up on this "functionality"?

The URL it tries to visit is, and
searching the Internet for that FQDN yields some details of how it
works.  If it can't retrieve the expected text at that URL, Windows 
will order IPv6 to the bottom of its address preference table (by
tweaking its internal RFC3484 rules).  The success (or failure) to
get to that IPv6 site is remembered for that network for 30 days,
and then re-tested.  I don't know how to encourage it to try a
fresh test, but there must be a registry setting to force that to


> - Mike

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