XDMCP not working in ipv6, gdm should be compiled with --enable-ipv6=yes

Thank you for your bug. Could you try with an another "client" than feisty to determine if the problem comes from the server or the client?

I've tried with an breezy livecd and I get the same issue...

There is no error in the logs on the 'server'. The only thing that appears in the logs is that pam has successfully opened a session for the user and immediately after closed it.

The client is an X86 and the server is a PPC

The connection is made by ipv6

Ok it's an ipv6 issue... I have to blacklist the ipv6 module on the 'server' to make it works. It seems that gdm try to connect in ipv4
(/usr/bin/Xnest :20 -br -br -audit 0 -name Xnest -auth /tmp/.gdmQRU2JT -terminate -query 192.168.1.133 -fp /usr/share/fonts/X11/misc,/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType,/usr/share/fonts/X11/misc/,/usr/share/fonts/X11/Type1/,/usr/share/fonts/X11/100dpi/,/usr/share/fonts/X11/75dpi/ -display :0)

but the connection is made in v6 (according to wireshark)

thank you for forwarding the bug, marking confirmed

The problem appears to be that the XDMCP client only adds the IPv4 address of the server to the access control list and not the IPv6 address.

Building gdm with ipv6 support makes this problem go away (--enable-ipv6=yes). Any reason this isn't done by default?

I've recompiled with --enable-ipv6=yes, same problem...

In fact the negotiation is made in ipv4 (xdmcp port) and the export display is made in v6

If I change the -query option to the server ipv6 address, the screen stay black, with wireshark I see that the server doesn't event open his xdmcp port in v6 to negotiate the connection.

I just have a look at the auth file

Using authority file /tmp/.gdm1TUMLT
xauth> list
#ffff##:20 MIT-MAGIC-COOKIE-1 be4aaa905e5cf980cfe10715b9e1258b

As I said on the gnome bugzilla compiling both server and client with --enable-ipv6=yes solve the problem.

That's fixed with that upload:

 gdm (2.17.6-0ubuntu2) feisty; urgency=low
 .
   * debian/rules:
     - build with --enable-ipv6=yes

The trouble is that with this fix it now no longer works using IPv4.

A quick Google search suggests that it is known that GDM's XDMCP does not simultaneously support IPv4 and IPv6. The above fix has therefore broken IPv4 support.

Can you make available separate binary packages for IPv4 and IPv6 users?

Reopening

xdmcp was working for me with both ipv4 and ipv6 when compiled with --enable-ipv6=yes

Could you open a new bug rather than using a closed one?