SSH, The Secure Shell: The Definitive Guide, 2nd Edition

Forwarding

Forwarding or tunneling is the use of SSH to secure another network application, covered fully in Chapter 9. Both PuTTY and Plink can set up secure tunnels for this purpose.

18.6.1 Forwarding with PuTTY

Forwarding is set up with the PuTTY Configuration dialog. For local port forwarding, which is the most common type, select Tunnels. Then fill in these fields:

Source port

Any unused TCP/IP port on your local machine.

Destination

The remote SSH server name, followed by a colon, followed by the remote port number.

Local/Remote/Dynamic

Choose Local.

For example, to connect to a remote VNC server (port 5900) on server.example.com, you’d provide a destination of server.example.com:5900, and any unused source port (say, 12345). This example demonstrates local forwarding [9.2.1], but PuTTY can also do remote [9.2.1.2] and dynamic [9.3] port forwarding.

To turn on X forwarding [9.4] for secure connections with an X Window server, simply choose Tunnels again and select the checkbox Enable X11 Forwarding.

To turn on agent forwarding [6.3.5] to allow your SSH agent to communicate with clients on other machines, navigate to Connection/SSH/Auth and select the checkbox Allow Agent Forwarding.

18.6.2 Forwarding with Plink

To enable the various kinds of forwarding with the command-line program Plink:

Local port forwarding [9.2.1]

Use the -L option, supplying the source port, remote server name, and remote port. For example, to forward local port 12345 to remote port 5900 on server.example.com, run: ...