smart_reverse_tunnel

smart_reverse_tunnel is a project that simplifies the setup and management of reverse SSH tunnel based on autossh. It includes a shell script and a systemd service to ensure reliable and persistent connections.

Components

Script: smart_reverse_tunnel.sh

This shell script automates the process of establishing a reverse SSH tunnel. It ensures that the tunnel remains active and automatically reconnects if the connection drops.

Functionality

The script scans all network interfaces, checks their metrics, and starts establishing the tunnel from the interface with the lowest metric. It pings the remote host to ensure connectivity. If the tunnel cannot be established, it moves on to the next interface with a higher metric and continues this process.

Systemd Service: smart_reverse_tunnel.service

The systemd service file configures and manages the smart_reverse_tunnel.sh script, ensuring it starts at boot and keeps running continuously.

Features

• Automatic Reconnection: Ensures that the reverse SSH tunnel is always active.
• Interface Selection: Automatically selects the best network interface based on metrics.
• Easy to Configure: Simple setup with minimal configuration.
• Systemd Integration: Seamless integration with systemd for automatic startup and monitoring.

Variables

The script smart_reverse_tunnel.sh includes several variables that need to be configured according to your environment:

REMOTE_HOST="10.10.10.10"
REMOTE_PORT=22
REMOTE_USER="remoteuser"
REVERSE_TUNNEL_PORT=2221
LOCAL_TUNNEL_PORT=222
PRIVATE_KEY_PATH=""
PING_TIMEOUT=2

• REMOTE_HOST: The IP address or hostname of the remote server.
• REMOTE_PORT: The SSH port on the remote server.
• REMOTE_USER: The username to use for the SSH connection.
• REVERSE_TUNNEL_PORT: The port on the remote server for the reverse tunnel.
• LOCAL_TUNNEL_PORT: The local port to forward.
• PRIVATE_KEY_PATH: Path to the SSH private key (if applicable).
• PING_TIMEOUT: Timeout for the ping check to ensure the tunnel is active.

The script smart_reverse_tunnel.service includes several variables that need to be configured according to your environment:

[Service]
ExecStart=/home/localuser/scripts/smart_reverse_tunnel.sh
#User=localuser #Uncomment when run this systemd service as root user

Installation of autossh

Debian

sudo apt install autossh

Fedora

sudo yum install autossh

Usage

Running as Root

1. Copy the smart_reverse_tunnel.sh script to your desired location (e.g., /home/localuser/scripts/).
2. Adjust the script and service file as needed.
3. Ensure the script has executable permissions:

   chmod +x /home/localuser/scripts/smart_reverse_tunnel.sh

4. Move the smart_reverse_tunnel.service file to the systemd directory:

   cp smart_reverse_tunnel.service /etc/systemd/system/
   systemctl daemon-reload

5. Enable and start the systemd service:

   sudo systemctl daemon-reload
   sudo systemctl enable smart_reverse_tunnel.service
   sudo systemctl start smart_reverse_tunnel.service

Running as a Regular User

1. Copy the smart_reverse_tunnel.sh script to your desired location (e.g., /home/localuser/scripts/).
2. Adjust the script and service file to match the user's environment.
3. Ensure the script has executable permissions:

   chmod +x /home/localuser/scripts/smart_reverse_tunnel.sh

4. Move the smart_reverse_tunnel.service file to the user's systemd directory:

   mkdir -p ~/.config/systemd/user
   cp smart_reverse_tunnel.service ~/.config/systemd/user/
   systemctl --user daemon-reload

5. Enable and start the systemd service for the user:

   systemctl --user enable smart_reverse_tunnel.service
   systemctl --user start smart_reverse_tunnel.service

6. Make sure the user services are started at login:

   loginctl enable-linger $(whoami)