SSH: Port Forwarding

Port Forwarding - The Problem (1)

  • Remote port is unreachable (behind a firewall)

  • Remote computer has a service running

  • That service listens on port 1234

  • The service’s protocol is not encrypted

  • ⟶ remote admin denies access through the firewall. Right he is!

  • I have SSH access to the remote computer because I am trusted.

Port Forwarding - The Problem (2)


Port Forwarding - The Solution (1)

Hmmm …

  • I am trusted ⟶ I have access to the remote computer via port 22/ssh

  • ⟶ I can login to the remote computer

  • ⟶ I can do there whateer I am permitted to

  • ⟶ I can login to the remote computer and connect to port 1234

Hmmm …

Then it cannot be a security risk if I automate the entire process

Port Forwarding - The Solution (2)


Port Forwarding - The Commandline

Creating the tunnel during login

$ ssh -L 5678:
  • Rather than connect to remote computer on port 1234 (remember: not possible because of firewall), the client connects to port 5678 locally

  • As a reaction, SSH server (“daemon”, sitting on the remote computer) connects to port 1234 on remote machine

  • Client (local/5678) and service (remote/1234) are “virtually” connected