Yesterday's Windows update causes IPv4 to be default
Dale W. Carder
dwcarder at wisc.edu
Thu Nov 15 04:52:26 CET 2012
On Nov 14, 2012, at 4:20 PM, Dan Wing wrote:
>> 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 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
So, what happens when there is a captive portal to force daily
registration such as at hotels or for corporate guests? With this
algorithm it would appear that ipv6 would be effectively permanently
disabled even though the network is dual stacked.
Or am I missing something?
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