Two Servers Behind NAT Router
Of course, it's possible to run more than one node per server. But if your server is low on resources (maybe a Pi) or you just want another server, it can be easily done. The concept is simple; because multiple servers behind a NAT router have one public IP address, each server will need it's IAX own port.
The IP address are examples, yours may vary. The default IAX port is 4569 but if you already chosen another port for the first server, that's fine, you can use it. Just pick a different port for the other server.
Remember to set the port you use for each server on allstarlink.org. If you forget this step external (to your network) nodes will not be able to connect.