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  |                    |
                                                -----------                    --------------                     |
                                                      |                                                           |
                                                       -----------------------------------------------------------

On localhost forward port 2222 to hidden's port 22:

ssh -L 2222:172.16.0.42:22 gateway

Then you can e.g. scp from localhost to hidden by using localhost's port 2222:

scp -P 2222 file1 localhost:

See also

• set up NAT