SSH X11 forwarding broken on Xenial When IPv6 is disabled

[Etienne Papegnies]

ouroumov@Edge:~$ ssh -X ouroumov@10.42.0.1 pluma
ouroumov@10.42.0.1's password:
X11 forwarding request failed on channel 0

(pluma:30718): Gtk-WARNING **: cannot open display:
ouroumov@Edge:~$

This used to work in 16.04.
This is problematic because among other things, it prevents one from using x2x.

Note: in this experiment, the ssh command is executed on a Zesty client, and the target is a Xenial Server

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: ssh 1:7.4p1-10
ProcVersionSignature: Ubuntu 4.10.0-22.24-generic 4.10.15
Uname: Linux 4.10.0-22-generic x86_64
ApportVersion: 2.20.4-0ubuntu4.1
Architecture: amd64
Date: Wed Jun 14 10:39:17 2017
InstallationDate: Installed on 2017-04-05 (70 days ago)
InstallationMedia: Ubuntu-MATE 17.04 "Zesty Zapus" - Beta amd64 (20170321.1)
PackageArchitecture: all
SourcePackage: openssh
UpgradeStatus: No upgrade log present (probably fresh install)

[Etienne Papegnies (etienne-papegnies)]

Nervermind, something is wrong with the server I think, I've tried against a Trusty machine and it works fine.

[Colin Watson (cjwatson)]

If you use the -v option then you should be able to find out the reason. It might be as simple as the server not having xauth installed.