• Download and install the RaspBerry Pi Imager
• Copy “RaspBerryPi OS Lite” to the SD card

• Boot from SD card
• Update all packages
• Enable SSH server in Interface Options and set location and keyboard in Localisation Options:

  sudo raspi-config

• Change host name
• Config SSH and generate SSH keys
• Exchange public key files
• Install missing packets:

  apt install autossh vim

Install AutoSSH on a remote_host to connect to a local_host to allow connections from this local_host or any_host from any (other) location.

1. Verify access from local_host and any_host: SSH from remote_host to local_host:<ssh_port_local_host> with key pair authentication and establish tunnel, requires <ssh_port_local_host> to be open on local location:

   remote_host$ ssh -R <port_to_access_remote_from_local>:localhost:22 user@<domain_name_of_local_host> -p <ssh_port_local_host>

2. Once confirmed, create file autossh-tunnel.service in /etc/systemd/system/:

   [Unit]
   Description=AutoSSH tunnel service Remote port <port_to_access_remote_from_local> to local 22
   After=network.target
   
   [Service]
   Environment="AUTOSSH_GATETIME=0"
   ExecStart=/usr/bin/autossh -o "ServerAliveInterval 10" -o "ServerAliveCountMax 3" -N -R <port_to_access_remote_from_local>:localhost:22 user@<domain_name_of_local_host> -p <ssh_port_local_host> -i /home/pi/.ssh/id_ecdsa
   
   [Install]
   WantedBy=multi-user.target

   We need to tell SSH the identity file as systemd will run as root. The environment variable is added so the autossh service can run in the background.

3. Once we have the service file created start the service and enable it to run at boot:

   remote_host$ sudo systemctl daemon-reload
   remote_host$ sudo systemctl start autossh-tunnel.service
   remote_host$ sudo systemctl enable autossh-tunnel.service

4. Trouble shoot:

   sudo journalctl -u autossh-tunnel.service [-b]

1. SSH from local_host to remote_host through tunnel at <port_to_access_remote_from_local>

   local_host$ ssh pi@localhost -p <port_to_access_remote_from_local>

1. SSH to local_host and establish tunnel from (any_host) <port_to_access_remote_from_local> to localhost:<port_to_access_remote_from_local>
2. SSH from any_host to localhost:<port_to_access_remote_from_local>

Connections from any location cannot tunnel to other services on the remote network directly. Instead, we can open a (temporary) tunnel to any host on the remote network and add a tunnel to the same port to the connection from any_host to local_host.

1. Login to remote_host, then establish an additional tunnel:

   remote_host$ ssh -R <port_to_access_additional_service>:host_on_remote_network:<port_to_additional_service> user@<domain_name_of_local_host> -p <ssh_port_local_host>

2. SSH to local_host and establish tunnel from (any_host) <port_to_access_additional_service> to localhost:<port_to_access_additional_service>
3. Connect from any_host to localhost:<port_to_access_additional_service>
4. Example: to access a https website on remote host 192.168.1.1, host_on_remote_network=192.168.1.1, <port_to_access_additional_service>=50443, <port_to_additional_service>=443

• SSH tunneling with Autossh