What Is Reverse SSH Tunneling? (and How to Use It)

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Reverse SSH tunneling is a technique used to establish a secure connection from a remote computer or device back to your local computer through an SSH (Secure Shell) connection. This technique is often used to bypass firewall restrictions, access resources on a private network, or manage remote devices securely.

Here’s how reverse SSH tunneling works and how to use it:

How Reverse SSH Tunneling Works:

Normally, when you establish an SSH connection, you initiate it from your local computer to a remote server. With reverse SSH tunneling, the connection is initiated from the remote computer back to your local computer.

  1. Initiation: On your local computer, you’ll create an SSH server that listens on a specific port. This server is set up to accept incoming SSH connections.
  2. Remote Connection: On the remote computer, you initiate an SSH connection to your local computer using the external IP address or hostname of your network. This connection is made to the port you specified for the SSH server.
  3. Tunnel Setup: As part of the SSH connection, you also set up a tunnel that allows traffic to be forwarded from the remote computer through the SSH connection and into your local network.
  4. Access: With the tunnel established, you can use the remote computer to access resources on your local network as if you were physically present there.

How to Use Reverse SSH Tunneling:

  1. Configure SSH Server on Local Computer:
    • Install an SSH server on your local computer if you haven’t already. On Linux, OpenSSH is commonly used.
    • Configure the SSH server to listen on a specific port (not port 22, which is the default) and allow tunneling.
  2. Access Remote Computer:
    • On the remote computer, initiate an SSH connection using the external IP address or hostname of your local network. Specify the port you configured in the previous step.
    • Use the -R flag to set up the reverse tunnel. For example:
      ssh -R 2222:localhost:22 user@your-local-ip

      This command forwards connections on the remote port 2222 to your local SSH server’s port 22.

  3. Access Local Resources:
    • Once the tunnel is established, you can use the remote computer to access resources on your local network.
    • For example, you can SSH into your local computer from the remote computer using the forwarded port:
      ssh -p 2222 user@localhost
  4. Secure the Connection:
    • Ensure that the SSH server on your local computer is properly secured with strong passwords or key-based authentication to prevent unauthorized access.

Reverse SSH tunneling can be a powerful tool for remote management and access to resources. However, it requires some technical knowledge and careful configuration to ensure security. Always use strong authentication methods and consider the security implications of opening ports and establishing tunnels on your network.