# SSH Port Forwarding

**Port forwarding** secures connections by tunneling local or remote ports through SSH. Useful for accessing services behind firewalls or across untrusted networks.

Local forward: traffic from your localhost goes through SSH to a service on the remote side.

```bash
$ ssh -L 8000:localhost:3000 user@host
```

Now `localhost:8000` connects through `host` to its `localhost:3000`. Useful for accessing a database or web service on a remote server.

Bind to all interfaces (less secure):

```bash
$ ssh -L 0.0.0.0:8000:localhost:3000 user@host
```

Remote forward: traffic from the remote host comes back through SSH to your machine.

```bash
$ ssh -R 8000:localhost:3000 user@host
```

Now `host:8000` connects back through SSH to your `localhost:3000`. Useful for exposing a local service to a remote network.

SOCKS proxy: use SSH as a proxy for all traffic.

```bash
$ ssh -D 8000 user@host
```

Clients can configure `localhost:8000` as a SOCKS5 proxy. Browser, curl, or other apps route traffic through the tunnel.

Persist tunnels in `~/.ssh/config`:

```
Host work
    HostName work.example.com
    LocalForward 8000 localhost:3000
    RemoteForward 8000 localhost:3000
```

Common options:

```
-L [bind_address:]port:remote_host:remote_port
-R [bind_address:]port:local_host:local_port
-D [bind_address:]port
-N             don't execute commands (just forward)
-f             run in background
```

Keep tunnel alive in background: `ssh -NfL 8000:localhost:3000 user@host`