How to Fix SSH (and git) Not Working Over Wireguard on Mobile Hotspot

I had the issue on my ChromeOS, that through the Wireguard VPN internet connections were working, but ssh was not working - and neither was git pull, since I was cloning via SSH.

The command ssh $ip -vvv got stuck on debug1: expecting SSH2_MSG_KEX_ECDH_REPLY, which apparently is an issue commonly caused by the MTU being to big.

I first couldn't debug the issue, since the SSH in the ChromeOS terminal was working - it was only not working from within the Linux VM in ChromeOS. Therefore, the root cause was the MTU value not being propagated properly into the Linux VM within ChromeOS.

I could find a suitable value by using the following ping command ping -M do $ip -s 1337, where the value of 1337 was adjusted until it didn't work anymore. Linux had an MTU of 1500 set (found by using ip a | grep mtu), and the highest working packet size for me was 1392.

Then I just adjusted the MTU size as follows:

sudo ip link set dev eth0 mtu 1337

And afterwards everything was working from within the Linux VM over wireguard!