solve: "X11 forwarding request failed on channel 0" problem after disable ipv6 of centos

1. Started sshd in debug mode (sudo rc.d stop sshd, sudo /usr/sbin/sshd -d)
2. Noticed Failed to allocate internet-domain X11 display socket. in debugging output
3. The page http://forums.fedoraforum.org/showthread.php?t=270333 indicates a possible relation to IPv6 being disabled.
4. Checked sysctl net.ipv6.conf.all.disable_ipv6, and indeed, IPv6 was disabled.
5. Re-enabled by undoing https://wiki.archlinux.org/index.php/IPv6_-_Disabling_the_Module
5'. Alternatively, adding AddressFamily inet to /etc/ssh/sshd_config would have also worked


comments: the (5) is good if you have to disable ipv6.