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.
-- XDMCP not working in ipv6, gdm should be compiled with --enable-ipv6=yes https://launchpad.net/bugs/75254 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
