Da documentação do SSH em encaminhamento de porta :
It is important to realize that if you have three hosts, client, sshdserver, and appserver, and you forward the traffic coming to the client's port x to the appserver's port y, only the connection between the client and sshdserver will be secured. See Figure Forwarding to a third host. The command you use would be something like the following:
ssh2 -L x:appserver:y username@sshdserver
alt text http://www.ssh.com/support/documentation/online/ssh/adminguide/32/tunnel2-2.gif