SSH tunneling quick example
ssh bridge-machine -L local-port:destination-machine:destination-port -N
bridge-machine is the machine providing an ssh server that will act as a bridge to the
destionation-machine. The destionation machine could be, for instance, a database, a Redis server, etc, that is not accessible from your network, but is accessible via another server (the bridge) that you are able to access via SSH.
I always forget which port is the local one is which is the remote. One nice mnemonic is to remember that Left is Local, Right is Remote.
In the end,
bridge-machine will be connected to
destionation-machine:destination-port and that connection will be exposed in your local port
-L provides the tunnel configuration,
-N tells SSH to not open a terminal. This command will steal your terminal. If you don't want that, use the
-f option to tell SHH to run on the background.