Yes, you need to perform port forwarding on the ADSL router. For more detailed steps, please post your ADSL router model/make here, or use that information to find the correct steps from www.portforward.com.
Originally Posted by weks87
You also need to allow the ports for SSH and FTP (22 and 21 by default) on your server's firewall, if you have activated it. On Ubuntu, the usual firewall settings utility is ufw. You can allow the ports (for example) with the command
Once you have SSH access, you can change any settings remotely in the future.
sudo ufw allow 22
sudo ufw allow 21
One important point: Most routers have SSH and (T)FTP servers built into them; if you are using the default ports for SSH and FTP, aside from forwarding them properly, you also have to disable WAN-side (Internet-side) access to the ROUTER's SSH and FTP services. When you do this however, you can no longer remotely change settings on the modem; you will have to ssh to your server, and from there, ssh (locally) to your router. If the router's settings are shot, you will not be able to reach your server, and hence you will not be able to remotely fix the router. Do I make sense?
If you use non-standard ports, this is not an issue.
Most router's have a built in method to use (for example) a dynamic ip forwarding service such as dyndns.org. Or, ubuntu comes with a client that will work with dyndns.org. Please visit the website and setup a free account; it will be far more elegant than your method.