Yesterday's Windows update causes IPv4 to be default

Dan Wing dwing at
Mon Nov 19 22:59:55 CET 2012

> -----Original Message-----
> From: at [mailto:ipv6-
> at] On Behalf Of Phil Mayers
> Sent: Monday, November 19, 2012 2:26 AM
> To: ipv6-ops at
> Subject: Re: Yesterday's Windows update causes IPv4 to be default
> On 11/19/2012 03:26 AM, Christopher Palmer wrote:
> > Networks with captive portals are exempt from the change. Once/if the
> > user escapes the portal (by paying for service or whatever), than the
> > heuristic will take effect as described.
> >
> What does windows consider a captive portal, and what does it consider
> an escape?

Same mechanism Windows has been using for several years -- it tries to
resolve (by doing an A record query) and download 
ncsi.txt from there.  And probably validates the IPv4 address returned
in the A record.  I'm sure there are lots of details online.  If that
fails, then it determines the computer is behind a portal and displays
a "!" on the network indicator.  After the user satisfies the portal 
(providing the hotel room number or whatever) and becomes 
accessible, the "!" is removed from the network indicator, and at that
time the IPv6 probe is run.

> It would be really good if there was a low-level description of all the
> intelligence in the newer versions of the windows IP stack - detailed,
> with state diagrams and transition conditions, per-product notes, etc.


More information about the ipv6-ops mailing list