Clients connect successfully but there’s no level 3 communication. The TUN/TAP interface is up but lacking IP address and routes are missing, too. The OpenVPN log file at /var/log/openvpn/openvpn.log shows the following, in particular no errors have been logged:
/sbin/ip addr add dev tun_vpn local 10.7.0.1 peer 10.7.0.2 /sbin/ip route add 10.7.0.0/24 via 10.7.0.2
We’re running Debian Linux kernel version 4.19.0-2-amd64 .
There’s not much to be found matching this exact setup/failure combination. The basic issue however is not uncommon. Somewhere there was some kernel version posted regarding a similar issue, the kernel version was more recent that our local kernel version. This possibly caused the same issue, in conjunction with an update that was introduced to openvpn. This was a valuable hint to update our kernel. Bad thing if you’re working with an embedded device for which no BSP nor updates are available. Luckily, in this case we are able to update to Linux kernel version 5.4.0-4-amd64 . And.. it worked. Easy. If you know how.
Issue solved. Ticket closed.
Nota bene: You might want to use wireguard.