SSH Tunneling
Forward Tunneling
Suppose we have a machine with public IP and want to use it as a bridge to another machine (either with or without public IP), we can run the following command on the local machine:
ssh -p<port> -L <local port>:<destination address>:<remote port> -N <user>@<public address>
where
<port>is the ssh port of the bridge machine, i.e., the<public address><address>is the address of the bridge machine, usually a VPS<local port>is the port opened on a local machine through which we can reach<destination address>:<remote port><destination address>is the address that we want to reach
Reverse Tunneling
Suppose we have a machine that is behind a firewall and wants to access it from outside. We will need a publically accessible machine. Then we can run the following command on the machine that is behind the firewall:
ssh -p<port> -N -R <port to open>:localhost:<local port> <user>@<public address>
where
is the ssh port of the <public address><public address>is the address of the publically accessible machine<port to open>is the port to be opened on the public machine, which is then used to reach the machine that is behind the firewall<local port>is the port (open ssh port) opened on the machine that is behind the firewall.