I solved this problem for myself yesterday and couldn’t find the answer anywhere online (clearly stated), so here’s what I did.
This also works for Plex, games, etc it’s policy based routing so you can have your VPN and remote access at the same time.
This configuration is for your ssh server (ie your home PC) that has a VPN running like ProtonVPN etc and allows you to connect back to your home PC remotely either for SSH, plex, anything you’re serving.
This is changing the default gateway for particular ports, so that return traffic from connection attempts doesn’t go back out through the VPN.
I used this page to figure out how to do this:
http://linux-ip.net/html/tools-ip-rule.html
Add a default route to some table, arbitrarily table 10 but you can use whatever number (RTFM), also obviously needs to be your router IP
sudo ip route add default via 192.168.19.1 table 10
Add a rule for the return traffic from your ssh host
sudo ip rule add sport 22 table 10
sudo ip route flush cache
check out your fancy new rule
ip rule show
And to make this persistent across reboots, add to:
/etc/systemd/network/20-wired.network
(or whatever your file there is, add the following to the bottom. This is the same as above, just permanent)
[Route]
Gateway=192.168.19.1
Table=10
[RoutingPolicyRule]
SourcePort=22
Table=10
Goddamn I didn’t even think of that, I spent days on an alternate solution to a problem this would’ve solved.
I spent most of the day intensely learning nftables and ulogd thinking that was the way. Nope, there was a simple way all along.