Yesterday's Windows update causes IPv4 to be default

Brian E Carpenter brian.e.carpenter at gmail.com
Wed Nov 21 09:56:08 CET 2012


(Christopher Palmer, you may want to not read this :-)

On 15/11/2012 16:55, Brian E Carpenter wrote:
> On 15/11/2012 11:09, Dick Visser wrote:
>> On 14 November 2012 23:20, Dan Wing <dwing at cisco.com> wrote:
>>
>>> The URL it tries to visit is http://ipv6.msftncsi.com/ncsi.txt, 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
>>> occur.
>>
>> It looks like there is, see attached regedit screendump.
> 
> Thanks for that. It looks as if one should clear
> EnableActiveProbing to get rid of this feature.

Alternatively, find the IPv4 address of www.msftnsci.com,
in my case 23.62.53.58,

and then add an entry to your hosts file like this:

#confuse the Windows v6 connectivity test by pointing it to IPv4
23.62.53.58     ipv6.msftncsi.com

It works beautifully. (In fact, since I have a good SixXs tunnel,
Windows prefers IPv6 anyway, so I only did this to see if it
worked. However, it does show once again that hacks can be hacked.)

     Brian


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