Yesterday's Windows update causes IPv4 to be default

Dan Wing dwing at
Thu Nov 15 18:20:59 CET 2012

> -----Original Message-----
> From: Sander Steffann [mailto:sander at]
> Sent: Thursday, November 15, 2012 9:09 AM
> To: Dan Wing
> Cc: Mike Jones; Tassos Chatzithomaoglou; <ipv6-ops at>
> Subject: Re: Yesterday's Windows update causes IPv4 to be default
> Hi,
> > The stability of is quite good now.  I know of
> > several probes checking it frequently, from different locations.
> Ok, let's rephrase that to 'an outage somewhere between the user and
>'. Depending where the outage is the impact will be
> smaller/larger. It is still a very big step to go from
> ' is unreachable' to 'prefer IPv4 for all traffic for
> 30 days'.

Yep.  And the corollary, the IPv6 path to works
fine but the IPv6 path to $OTHER_DOMAIN is broken.

> I hope the algorithm is better than it seems from this discussion. It
> wouldn't be as bad if i.e. the result is cached for 30 minutes instead
> of 30 days :-)

The only official documentation from Microsoft is
the key section is

   "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.

    To make sure that Windows 8 does not cause problems on
    enterprise networks, the functionality has two safeguards:

    * If the enterprise has provided specific routing information
    to a particular destination, then Windows 8 will honor that
    preference, regardless of the connectivity determined by
    Windows. In enterprise environments, Windows assumes that
    network administrators who configure such routes specifically
    thought it was a good idea to use those routes. 
    * This change isn't implemented on networks with web proxies. 
    In these networks, the proxy provides connectivity to the 
    Internet; so end-to-end testing of IPv6 connectivity is 
    not useful.  Instead, Windows 8 simply opens connections 
    to the proxy in the most efficient manner possible."

I have begged for a more technical document to no avail.


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