SSH Port Forwarding (SSH tunneling ) in Linux machines.

SSH Port Forwarding allows us to communicate with any remote server in secured way.
Here a port in a local machine will be configured to forward requests to  a destination  web or  mail servers through SSH tunnel established with any other server.

The command used to accomplish this scenario is  given below.

ssh -L localport:host:hostport user@ssh_server -N 

where: 
-L - port forwarding parameters 

localport - local port (chose a port that is not in use by other service) 

host - server that has the port (hostport) that you want to forward 

hostport - remote port 

-N - do not execute a remote command, 

user - user that have ssh access to the ssh server (computer) 

ssh_server - the ssh server that will be used for forwarding/tunneling 

Without the -N option you will have not only the forwarding port but also the remote
shell. Try with and without it to see the difference. 

We can have multiple  '-L' parameters used for  multiple port forwarding for  different services like, HTTP, SMTP, POP.

See some examples. :)

ssh -L 8888:www.myhost.com:80 user@ssh_host -N 

ssh -L 8888:www.myhost.com:80 -L 110:mail.myhost.com:110 \ 
25:mail.myhost.com:25 user@ssh_host -N