SSH Port Forwading and Tunneling

Sometimes it's useful to forward a port from a source to a target machine. For instance port forwading itself is used by a router, which creates a sub network. In that case routers act as port delegators.

Port forwarding has a security function as well. For example you want to hide your web server from your public network. So you can tunnel your HTTP port from your secured to your public network machine.

The following examples describes how to forward a remote or a local port via SSH. Typically SSH forwards to localhost (127.0.0.1). To change this you have to set the GatewayPorts parameter to yes (/etc/ssh/sshd_config).

Remote Port Forwading example:

#you want to forward a local port to a remote machine
ssh -v -g -R remoteport:localhost:localport root@remotehost

#e.g. forwarding my local webserver on port 8080 to http://developers-blog.org:80
ssh -v -g -R 80:localhost:8080 root@developers-blog.org

#to bypass the ClientAliveInterval you can append a while loop to hold up the SSH connection
ssh -v -g -R 80:localhost:8080 root@developers-blog.org "while [ 1 ]; do sleep 10; echo '\''loop step'\''; done"

Local Port Forwading example:

#you want to forward a remote port to my local machine
ssh -v -g -L localport:remotehost:remoteport root@remotehost

#e.g. i want to see my local webserver on my
ssh -v -g -L 8080:developers-blog.org:80 root@developers-blog.org

#for bypass the ClientAliveInterval you can append a while loop as well
ssh -v -g -L 8080:developers-blog.org:80 root@developers-blog.org "while [ 1 ]; do sleep 10; echo '\''loop step'\''; done"

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