Port forwarding & relaying

Is port forwarding necessary on both network firewalls to avoid using Relaying?

I assumed that if I have port-forwarding set-up on one network firewall, that devices in the other network should be able to connect without relaying. But, so far, the devices are not connecting unless relaying is enabled.

In theory yes, one should he enough, but the forwarded port must be the same as the port its listening on.