Linux HowTo: Secured Shell Tunneling - Poor Man's VPN

-ssh Tunneling is also called port forwarding.
-ssh Tunneling = port forwarding  = poor man's vpn = a way to forward otherwise insecure tcp traffic through ssh.

-Utility of ssh Tunneling    = allows users to access securely their company data while remote (home, internet, etc)
-as long as the user has an ip conn to the Internet, he can connect to the remote server securely.

-ssh with -L option allows to tunnel ssh connection.
-using one hostA to connect securely to another hostB (ie via hostA)
            clientA# ssh -L local_port:hostA:dest_port   hostB
 ie:       clientA-----hostA====hostB
 ie:       user on clientA authenticates on hostA but securely connects to hostB.
 ie:       it is a way for people inside a firewall or proxy to bypass the firewall restrictions and get to the computers in the outside world.

Additional notes:

-ssh with -X option is a type of ssh tunneling. This makes use of ssh to Tunnel X Windows remotely -- note that X is an insecure protocol.

-Default port for X is 6000. If this port is blocked, a workaround is to run ssh with -X option to display X output.

-Example:  User mrinal wants to connect from Local node A running X server (and ssh Client) to node B running X client and ssh Server)

   On Node A:

     $ ssh -X mrinal@nodeB              -- user mrinal starts ssh Tunnel between node A & node B

-ssh with a lowercase -x disables the ssh tunneling and is not supposed to be used.