Yesterday's Windows update causes IPv4 to be default

Tassos Chatzithomaoglou achatz at
Wed Nov 14 17:59:49 CET 2012

/Assume that a computer is configured to use an IPv6 connection as the default connection.
Additionally, assume that the computer does not have a connection to an IPv6 network. In
this situation, it takes a long time for the computer to connect to an IPv6 site. //
//This issue occurs because Windows tries the IPv6 connection first. After the connection
fails because of a time-out error, Windows tries the IPv4 connection.//
//After this update is installed, Windows uses the NCSI functionality to examine the Ipv6
connection. If the connection is broken, Windows uses IPv4 instead of IPv6./


Dick Visser wrote on 14/11/2012 18:46:
> Hi
> I looks like yesterday's batch of updates causes Windows 7 to prefer
> IPv4 over IPv6.
> After (automatically) installing the whole lot, one of my users
> complained about connection issues with WinSCP to our web server.
> This runs SSH on IPv6-only. His WinSCP for some reason tried to
> connect over IPv4, without falling back to IPv6.
> I tried "ping" and that also used IPv4.
> "ping -6" did also work, but I'm pretty sure it used to
> default to IPv6.
> After clearing the cache in WinSCP things started to work again.
> I didn't install the updates (about 20, including the Office ones) on
> my own computer, so I had a look at them first.
> One of them is called "No network connectivity on Windows 7-based or
> Windows Server 2008 R2-based client computers when a DHCPv6 message is
> sent that has a duplicated DUID",
>, which is the only one that
> mentions IPv6.
> Before installing anything, I tried to "ping" and that
> used IPv6 all-right.
> I then installed all the updates except the suspicious
> After rebooting, "ping" uses IPv4...
> So I guess one of the other updates caused this; I'm now booting up a
> VM to investigate which one exactly.
> So far the no other major stuff broke, and it looks like only the
> default has changed, but I'd thought I mentioned it here anyway, just
> in case...
> Anyone else has seen IPv6 issues on Windows since yesterday?

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