ssh tunnels are magical

After getting the Pi connected upstairs, I figured it would be nice to be able to connect to it when I’m out and about. Now, I don’t have a static IP, and don’t really want to open ports to the Internet anyway, but I do have a shell account on the Oxford linux.ox.ac.uk machine. SSH tunnels to the rescue!

1. Add linux.ox.ac.uk to the Pi’s ssh config

   ~/.ssh/config on the Pi

   Host ox
       User <me>
       HostName linux.ox.ac.uk
   

2. Tell the Pi to autossh to ox on boot, and forward port 3141 there to port 22 here

   /etc/rc.local on the Pi

   su - pi -c 'autossh -f -N -R 3141:localhost:22 <me>@linux.ox.ac.uk'
   

3. Add a ProxyCommand on my machine that tells ssh “if you want to ssh to pi, instead of making the TCP connection yourself instead do this.”

   ~/.ssh/config on my machine

   Host pi
       User pi
       ProxyCommand ssh raven nc -q0 localhost 3141
   

Et voilà, ssh pi on my local machine now connects to the Pi via linux.ox.ac.uk.

Bonus: you can tell SSH to reuse connections by adding the following to config

ControlMaster auto
ControlPath .../.ssh/connections/%h_%p_%r