SSHtunnel

SSHtunnel, or SSH tunnel, refers to the technique of routing network traffic through an encrypted SSH connection. It uses an established SSH session to forward traffic between a local port and a destination reachable from the remote host, or the other way around, and can also create a dynamic proxy for multiple destinations.

There are three common forms of SSH tunneling. Local port forwarding (-L) forwards traffic from a local port to a destination on the remote side, for example: ssh -L 8080:internal.example.org:80 [email protected]. Remote port forwarding (-R) forwards traffic from a remote port to a local destination, such as: ssh -R 2222:localhost:22 [email protected]. Dynamic port forwarding (-D) sets up a local SOCKS proxy on a chosen port, for instance: ssh -D 1080 [email protected], allowing applications to route traffic through the SSH server via the proxy.

Common use cases include accessing internal resources behind a firewall from a remote location, securing traffic on public Wi‑Fi, or providing administrators with remote access to services without exposing them publicly. SSH tunnels can be used to bypass network restrictions or to securely administer remote systems.

Setup and security considerations are important. An SSH client and a server are required, and the server’s configuration may need to permit port forwarding (AllowTcpForwarding) and possibly GatewayPorts. For security, prefer key-based authentication, disable password login where possible, restrict tunneling to approved users, and monitor tunnel activity. Be mindful that tunneling can introduce exposure if misused, and performance may be affected by the additional encryption and routing overhead.

See also: SSH, port forwarding, SOCKS proxy.