For any kind of remote connection, the firewall on both the local and remote machine must be configured to allow the network traffic relating to the remote connection. If the computers are behind routers or firewall devices, these must be also be configured. Under SUSE Linux, this configuration is done by modifying the firewall component of YaST2.
For any other version of Linux, you'll need to examine the distribution's documentation to discover how to allow remote connections. For a router or firewall device, you should look within the documentation to see how "port forwarding" is set up.
To configure SUSE Linux's firewall, follow these steps:
Start YaST2 (select K menu ® Control Center ® YaST2 Modules) and click Security.
Click the Administrator Mode button and type your root password.
When the firewall configuration screen appears, click Next. This will show the configuration screen where the services you wish to allow through the firewall can be specified.
Make sure that SSH is checked. This will allow SSH and SFTP traffic.
To allow Remote Administration sessions, click the Expert button, just to the right of the line labeled Additional Services.
In the dialog box that appears, you can type in the individual port number of the application you wish to let through the firewall. You can also enter multiple ports in the input field by separating them with a space, and enter ranges by typing the first number, then a colon, and then the final number. For example, entering 22:40 indicates that ports 22 through 40 should be opened. In this case, you want to allow through port 5900, the standard port for VNC connections. So simply type this port number in the box and click OK.
Click Next, and then click Finish to restart the firewall with the new settings.