I have two computers behind the same router. Let's call them A and B.
A can SSH to B in the following manner:
ssh usr@<internal ip of computer>
B can SSH to A by doing the same, but the external IP must be used. I have forwarded port 22 of my router to the IP of computer A, so that all makes sense to me.
However, I want to also forward port 26 to computer B, and SSH from outside the network by using the external IP for both, but specifying either port 22 or 26, to effectively select which computer to use.
I have tried allowing port 26 through OUTPUT of iptables on A and INPUT of B, but that didn't seem to work. I have also forwarded port 26 to the internal IP of B (through the router), as I did with 22 for A.
Here's what I get when I try to SSH from A to B using the external IP and port 26:
ssh: connect to host xx.xx.xxx.xx port 26: Connection refused.
Versions: A = OpenSSH_5.9p1 Debian-5ubuntu1, OpenSSL 1.0.1 14 Mar 2012 B = OpenSSH_6.0p1 Debian-4, OpenSSL 1.0.1c 10 May 2012
A has 12.04 Ubuntu, B is a Raspberry Pi with Raspbian.
EDIT: Something that I forgot to put in: I did try switching the SSH config file (I found it is /etc/ssh/ssh_config) I uncommented (deleted the #) the line with Port and changed 22 to 26. It gave me the connection refused message still. (I rebooted to no avail.)