PuTTY bug x11-ipv6-breakage

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summary: Reported X forwarding breakage due to IPv6
class: bug: This is clearly an actual problem we want fixed.
difficulty: taxing: Needs external things we don't have (standards, users etc)
priority: historic: This is an old bug report that we think is either fixed without noticing, or confined to old systems, or too vague.
present-in: 2005-02-10 0.58

We've had a couple of reports of X forwarding breakage related to IPv6.

One report implied that X forwarding in PuTTY broke right after we integrated the IPv6 code. Presumably the IPv6 changes have had some sort of side effect on the local network connection between PuTTY and the X server, but it isn't clear what since we haven't been able to reproduce it.

We received this report by email (<41E6F012.2040105@ressukka.net>). Details include:

The symptom at the remote end is that X applications report "X connection to localhost:10.0 broken (explicit kill or server shutdown)".
The X display in the PuTTY configuration is the PuTTY default (equivalent to localhost:0). The reporter found that requesting 127.0.0.1:0 instead worked, although not consistently. (This leads me to wonder whether "localhost" might have been resolving to an IPv6 address on the system in question.)
The X server was xorg 6.8.1 from Cygwin.
Windows version was XP SP2.

Another report (<4E2CCFB2C8CC5244939D17374DC28E0003444974@ing.com>):

Windows XP Pro SP1
Connecting via an HTTP proxy
Same symptom ("explicit kill or server shutdown")
Using 127.0.0.1:0 doesn't help at all
X server doesn't matter (tried Exceed, Cygwin)
Still happens with "latest development snapshot" (2006-04)
Uninstalling IPv6 made the problem go away

PuTTY Event Log entries (approximate):

2006-04-12 12:44:08 Received X11 connect request from 127.0.0.1:39241
2006-04-12 12:44:08 Opening X11 forward connection succeeded
2006-04-12 12:44:08 Forwarded X11 connection terminated

If anyone is able to reproduce this or shed some light on possible causes, we'd be grateful.

SGT, 2024-11-17: classifying this bug as historic. It was last reported in 2006 when the IPv6 code contribution was new. It's had a lot of stabilisation since then, and I don't recall anyone reporting anything like this more recently.

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(last revision of this bug record was at 2024-11-17 14:53:03 +0000)