You can have as many servers running behind a public ip address, by using a router with port forwarding capabilities. For example if you have three linux servers with need of ssh access you can setup a port forwarding for each other like this
ex: Public ip:1.1.19.33
server1: 192.168.1.1 running ssh on port 22
server2: 192.168.1.3 running ssh on port 22
server3: 162.168.1.100 running ssh on port 22

Port forwarding:
192.168.1.1:22 - > 1.1.19.33:23
192.168.1.3:22 -> 1.1.19.33:22
192.168.1.100:22 -> 1.1.19.33:24


So you can access all of your servers from your public ip with different ports.
For server1 you use port23, for server2 use port 22 ........

If you need more help I can help you