I found lots of how-to guides already but none really matched what I wanted to achieve and quite a few seemed pretty out of date, with commands for RouterOS that no longer work.
What I wanted to end up with is something like this:
So fairly standard for a VPN but I was keen that once set up, it just keeps working. Things at Site A on 192.168.88.0/24 subnet should be able to access things at Site B on the 192.168.89.0/24 subnet automatically. It also needed to survive a reboot of either router.
One big stumbling block I ran into with OpenVPN on Mikrotiks is that they don't support push-route so you can get the VPN server to push routes to the client(s). So in the end I had to set up static IPs for the VPN to use (on the 10.9.9.50/32 subnet) and static routes by IP address.
Worth noting that the Mikrotik routers also don't support OpenVPN over UDP but this wasn't an issue for me.
