ssh port forwarding / tunnel

Local Port Forwarding

Forward a local port to a remote host:

Forward local port 8080 to remote host's port 80.
Example: allow the local host to access a restricted webserver on the remote host.

• ssh -fN -L 127.0.0.1:8080:127.0.0.1:80 user@remote.example.com
  • -q = quiet
  • -f =  put ssh to background
  • -N = Do not execute a remote command
  • -L = local port forwarding
  • Note: the first "127.0.0.1" is optional and prevents to publicly open the 2223 port on the local host

Forward a port to a remote host via an intermediate "jump" host:

• ssh -fN -L 127.0.0.1:8080:remote.example.com:80 user@jump.example.com

Remote Forwarding / Reverse Tunneling

Open port 8080 on the remote host and forward it to port 80 on the local host.
Example: allow anyone on the remote host to access a restricted webserver on the local host.

• ssh -fN -R 8080:127.0.0.1:80 user@remote.example.com
• -R = remote forwarding

Useful Options

• -o ExitOnForwardFailure=yes
  • Exit if port forwarding cannot be established
• -o ConnectTimeout=5
  • Exit if connection cannot be made after 5 seconds of trying

Terminate the tunnel

• fuser -k -n tcp 8080
  • Terminates the tunnel by port number