...in just one and simple command :

[root@host ~]# ssh -fNT -L <local port>:localhost:<distant port> -R <distant port>:localhost:<local port> <host/ip to connect to> -l <trusted user>

God bless ssh :P

PS : by the way, you may have trusted your servers with an ssh key's exchange

• f : tells ssh to go to the background
• N : tells ssh there is no remote command to execute
• T : tells ssh to disable pseudo-tty allocation