Starting with RHEL4, the system only accepts local (socket-based) X11 server connections. This means that if you go to another Unix server and try forwarding X11 output by using DISPLAY variable to point to your RHEL4 box, it will no longer work.
Enabling TCP connections to X11
In order to make your RHEL4 system accept TCP connections for X11, here's what you need to do:
In /etc/X11/gdm/gdm.conf, uncomment the
line and change it to
That's it! Restart gdm and enjoy!