SSH tunnel with single hop, using systemd-networkd and autossh

David Runge — Sun, 01 Feb 2015 18:00:00 GMT

Recently I had the pleasure of setting up a SSH tunnel between two virtual machines that share no route and are located in two different subnets.
They can however reach each other via SSH, hopping their host.
Let's assume the following setup:

client1 (Arch Linux) has 10.0.5.2/24
client2 (Arch Linux) has 10.0.6.2/24
host (Debian) is 10.0.5.1/24 to client1 and 10.0.6.1/24 to client2

As I needed the two clients to be able to send mail to each other and reach each others' services, I did some digging and opted for a SSH connection using TUN devices (aka. "poor man's VPN").

The following is needed to set this up:

root access on both virtual machines (client1 & client2)
a user account on the host system
SSH (OpenSSH assumed) installed on all three machines

SleepMap (Posts about TUN)

SSH tunnel with single hop, using systemd-networkd and autossh