SSH Tunnels and SOCKS Proxy

Welcome to SSH Tunnels! These aren't physical tunnels, but secure connections that let you forward network traffic through an SSH server.

Think of it as creating a secret, encrypted pathway through a public network. This pathway lets you access services that might otherwise be blocked or insecure.

SSH tunnels are incredibly versatile for developers and system administrators. They help you:

• Bypass Firewalls: Access internal services not exposed to the public internet.
• Secure Unencrypted Traffic: Encrypt data that would normally travel insecurely (like old protocols).
• Access Restricted Resources: Reach services on a private network from a public one, or vice-versa.

Local Port Forwarding is when you connect a port on your local machine to a port on a remote machine (via the SSH server).

The SSH server acts as a middleman. Your local application connects to a local port, and SSH securely forwards that traffic to the specified remote host and port.

The syntax for local port forwarding is straightforward:

ssh -L [local_port]:[remote_host]:[remote_port] [user]@[ssh_server]

Here's an example to access a database running on db-server (port 3306) through your ssh-gateway server:

After running the command from the previous scene, you can now connect your local database client to localhost:8080.

All traffic you send to localhost:8080 will be securely forwarded through ssh-gateway.com to db-server:3306. This is great for accessing private databases or web services.

Remote Port Forwarding is the opposite of local forwarding. It allows you to expose a service running on your local machine to a port on the remote SSH server.

This means others can connect to a port on the remote SSH server, and their traffic will be forwarded securely to your local service.

The syntax for remote port forwarding uses the -R flag:

ssh -R [remote_port]:[local_host]:[local_port] [user]@[ssh_server]

Let's say you have a web server running locally on port 8000 and want to make it accessible to others via your ssh-gateway on port 8888:

Once the remote tunnel is established, anyone who can reach ssh-gateway.com can now access your local web server by connecting to ssh-gateway.com:8888.

This is useful for sharing a local development server with teammates or for webhooks that need to reach your local machine.

A SOCKS proxy allows you to route all your application's traffic (e.g., web browser, chat client) through the SSH server. This is often used for anonymizing browsing or bypassing network restrictions.

The -D flag creates a SOCKS proxy on a local port:

After running ssh -D 9999 user@ssh-gateway.com, you'll have a SOCKS proxy running on localhost:9999.

You then configure your web browser (or other application) to use localhost as a SOCKS5 proxy on port 9999. All your internet traffic from that application will now be routed securely through your ssh-gateway.

You're trying to access a private internal web service running on internal-app.local:80 from your local machine (localhost). You have SSH access to jump-host.com.

Which SSH command would you use to forward local port 8080 to the internal web service?

You've mastered SSH tunnels! We covered:

• Local Port Forwarding (-L): Access remote services from your local machine.
• Remote Port Forwarding (-R): Expose local services to the remote SSH server.
• SOCKS Proxy (-D): Route all application traffic through the SSH server for privacy or bypass.

These techniques are powerful tools for secure and flexible network access in development and administration.