Bind SSHD to ipv4

When you all of sudden run into "No X11 DISPLAY" when trying to forward X11 over ssh. Ask yourself if you recently disabled ipv6 on the sshd server. If the answer is yes then try the following to make sshd bind only to ipv4.

Add "AddressFamily inet" to /etc/ssh/sshd_config. Then restart sshd.