This guide explains how to set up remote connections from a computer on public Wi-Fi to a campus intranet server using a cloud computer, including SSH key generation, autossh installation, and automated service configuration.

Tutorial: Reverse SSH - Home Computer Connecting to Campus Intranet Server

This comprehensive guide provides step-by-step instructions on establishing remote connections for a computer connected to a public Wi-Fi network. The connections will be orchestrated through the use of a cloud-based computer, such as Amazon Cloud.

Terminology

• A: Refers to the computer connected to public Wi-Fi.
• B: Designates the cloud computer.
• C: Represents the laptop at home.

Setting Up the Connection from A to B:

1. Generate an SSH Key Pair: Begin by creating an SSH key pair on computer A to facilitate passwordless login to computer B. Execute the following command:

   ssh-keygen -t rsa # Press Enter for all prompts. The generated id_rsa.pub file will be located in the ~/.ssh/ directory.
   

2. Copy Public Key: Copy the public key from computer A to computer B using this command:

   ssh-copy-id -i ~/.ssh/id_rsa.pub ubuntu@666.666.666.666 -p 22
   

3. Install Autossh: Install autossh to guarantee automatic reconnection in the event of a disruption in the reverse SSH connection between A and B:

   apt-get install autossh
   

4. Test Connection: Verify the success of the autossh + passwordless login setup by running the following command:

   autossh -M 9991 -NfR 8990:localhost:22 ubuntu@666.666.666.666
   

   If the command on computer A runs successfully, and on computer B, you observe the port numbers in the red box when executing the command watch -n 1 netstat -tnlp, then the test is successful.

Configuring the Autossh Service:

1. Automate Autossh Startup: Automate the startup of autossh when computer A is powered on. Begin by creating an autossh.service file:

   vim /lib/systemd/system/autossh.service
   

   Insert the following content into the autossh.service file:

   [Unit]
   Description=Auto SSH Tunnel
   After=network-online.target
   
   [Service]
   User=YOUR_USER_NAME
   Type=forking
   ExecStart=/usr/bin/autossh -NR 9888:localhost:22 -i /home/YOUR_USER_NAME/.ssh/id_rsa ubuntu@666.666.666.666 -p 22 >> /dev/null 2>&1
   ExecReload=/bin/kill -HUP $MAINPID
   ExecStop=/bin/kill -TERM $MAINPID
   KillMode=process
   Restart=always
   
   [Install]
   WantedBy=multi-user.target
   WantedBy=graphical.target
   

2. Verify Configuration: Check if the autossh service is successfully configured:

   systemctl enable autossh
   systemctl start autossh
   

   Confirm the service’s status:

   systemctl status autossh
   

   If the service starts successfully, when running the command watch -n 1 netstat -tnlp on computer B, you should see the port numbers in the red box.

Connection from C to A:

To establish a connection from laptop C to computer A through computer B:

1. Connect to Computer B: Initiate an SSH connection to computer B using the following command:

   ssh ubuntu@666.666.666.666
   

2. Access Computer A: Open another terminal tab and connect to computer A:

   ssh -p 9888 YOUR_USER_NAME@127.0.0.1
   

   You should now have a remote connection from laptop C to computer A via computer B, enabling seamless access to your campus intranet server.