Port forwarding working for incoming traffic but not outgoing

Hello,

I have a licensing server. Other computers need to turn on a program, they send a message to the licensing server, and it responds that they have permission to run.

Until today the licensing server was plugged into its own ethernet wall socket and configured with a static IP address. Today I put a router into that wall socket and now the server's plugged into the router.

The router (WRT-54G) was set to the static IP - and now the internet on its network works. I set all ports to be forwarded to the server's internal IP address - and now my programs can detect and ping it. But now the server won't send back permissions to use licensed software, or even reply with a list of the software which it can license.

Is there something else besides port forwarding that I should setup?

First, I must ask the obvious question: Why did you move it behind a router?

How does the licensing server send back the permissions? TCP? UDP? UDP broadcast?

I suspect it might be UDP broadcast, and in that case it will not work behind a router.