Yesterday's Windows update causes IPv4 to be default

Christopher Palmer Christopher.Palmer at
Mon Nov 19 21:11:43 CET 2012

When we first join a network, an HTTP web request is sent to the NCSI beacon ( If we get content other than "Microsoft NCSI" - than we expect a captive portal is there.

We have a heuristic which determines when we'll reattempt the HTTP web request and go "green." This is based on TCP connection/path information, etc. Once you start going to a site or two, and our probe succeeded, then we'll go green.

Re: Documentation, I can't promise anything but I know it would be a considerable boon for operators and other networking experts.

-----Original Message-----
From: at [ 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?

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.

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