Without giving any information about your setup (No, saying that you have 3 interfaces is NOT giving information) noone will be able to help you.
Start with the basic things like:
How is your network set up (diagram, inclusive the used IPs),
what firewallrules you have where (screenshots of the rules),
NAT-rules (screenshots of them),
how you test (where is the testclient,
to what do you connect),
what you expect,
and what actually happens.