port forwarding

[Gerhard Magnus]

I have a single-Ethernet port DSL modem hooked up to a router which then
connects to two boxes running Linux.  I'm not using the DHCP server
built in to the router -- both boxes have explicitly assigned IP
addresses, 192.168.1.11 and 192.168.1.12 which appear in /etc/hosts.  I
want to set up port forwarding to allow ssh from the outside to
192.168.1.11 on port 22.  I've set the Fedora firewall "security level"
to "high" while allowing for the exception of incoming ssh.

Both the modem and the router have screens for setting port forwarding. 
My question is: do I have to set one or the other or both?  For example,
do I need to set the modem to forward port 22 to the router, and then to
set the router to forward port 22 to the 192.168.1.11?

I'm getting very interested in this networking technology and would also
appreciate any links or references that might be helpful, especially in
characterizing systems that include machines running different OS's.

Jerry