SSH allows the forwarding of X11 traffic. This is a very useful feature because X11 itself is not particularly secure, but SSH is. To use this feature, use the SSH client on a machine with an X11 server running:
Besides the usual function of SSH, the -X option specifies that the local X11 server be forwarded so that someserver can see it as an available X11 server. Once SSH makes the connection, you can run any X11 client on somehost (such as OpenOffice, Firefox, etc.). The X11 client runs on somehost, but the application will display on the machine that runs the SSH client.
This approach also simplies the network configuration. Most hosts and networks allow port 22 traffic through because SSH is a useful protocol. However, the default port of X11 (6000) may not be allowed through most firewall.