SSH - Left Tunnel (Left Port Forwarding) - Local to server

About

When you need to make a SSH connection to connect to a server, you can create a left tunnel (a left port forwarding) to reach the server as of it was direct reachable.

Illustration: Image Credit: How does reverse SSH tunneling work? from Erik

Usage

When you need to make a connection to a private database (in a private network), you can a SSH tunnel and reach it as of the database was local.

Steps

Create the tunnel

You can create the tunnel with any client such as:

ssh
or jsch

Ssh

Create the tunnel: From the client host:

ssh -N -T -l loginName -L8881:farAwayServer:8888 sshServerHost

where

localhost is the host seen from the ssh client
The local port is 8881 (The port of your machine)
farAwayServer is the server to reach (it can be the sshServerHost)
The server port is 8888
The loginName is loginName
N means no remote command
T disables pseudo-tty allocation (No terminal)

Jsch

Jsch is a java library.

JSch jsch = new JSch();
Session session = jsch.getSession(user, host, port);
localPort = 4321;
remoteHost = "localhost";
remotePort = 3306;
session.setPassword(password);
session.setConfig("StrictHostKeyChecking", "no");
System.out.println("Establishing Connection...");
session.connect();
int assigned_port = session.setPortForwardingL(localPort, remoteHost, remotePort);