Tunneling with OpenSSH

SSH Tunneling or SSH port forwarding is typically useful if you have a network with a private segment like this:

                                                                           -----------------------------------------------------------
                                                                          |                                                           |
                                                                          |                                                           |
                           ---------                                -----------                    --------------                     |
                          |localhost|------------------------------|   gateway |------------------|  hidden      |                    |
                           ---------                               | 10.2.2.18 |                  | 172.16.0.42  |                    |
                                                                    -----------                    --------------                     |
                                                                          |                                                           |
                                                                           -----------------------------------------------------------

ssh -L 2222:172.16.0.42:22 gateway