All software servers i have use like Apache, MySQL are automatically linked to their ports, so if i do nmap on the domain can see port 80 = Apache. But OpenSER a VOIP and SIP server tells me when i run it that it is listing on the ethernet device and the local loopback and i can connect to it when on the network, but when i try and connect to it outside of the local network from the domain it can't find the server. When i do a nmap, it does not even show the port as open or closed. There is no physical firewall between the server and the internet as it is a VPS and i just use IP tables, but i have only ever used those once, so i don't really understand how to set them up.

Can anyone give me any advice on how i get the software server to listen on the internet like Apache, MySQL, SSH, VNC etc... not just the internal network.

Thanks, Dave.