X11 forwarding on openssh server
On my recent server installations, I noticed that X11 connections were not being forwarded via ssh. Initially I thought it was because of lack of some core X11 libraries in server installation. However, today I found that it was this OpenSSH bug related to a mess up between ipv4/ipv6. From the bug report:
What happens is that in x11_create_display_inet() (channels.c),
getaddrinfo() apparently returns the IPv6 address family first, and
sshd only tries to bind to that.
I always disable IPv6 in my installations (unless needed) to avoid confusion, and that explained why X11 forwarding refused to work over ssh.
A workaround for this problem is to add the following line to
A similar problem also seems to affect Java networking according to this bug. I haven’t experienced it yet, but should remember just in case.