Set up multicast route across a middle hop

I have a host with two Docker containers (with NET_ADMIN capability): backend with an interface eth0 (172.16.7.3) openvpn-server with interfaces eth0 (172.16.7.2) and tun0 (10.8.0.1), running an OpenVPN server (tun mode) There is an OpenVPN client on another machine openvpn-client with interface tun0 (10.8.0.2). The VPN is working. Additional route setup: backend has routes 10.8.0.0/24…