+1
I'm facing the same problem. I've performed a careful search in the forum, but failed to find a decision.
So, I configured the port forwarding as topic starter did (except one difference: I don't use a virtual interface, but the real one; I've tried both "ip_address/32" and "Zetyal" as Original destination). Another difference is that I have eth2 as external interface, eth0 as internal one.
Moreover, I created the service RDP (protocol TCP, source port any, destination port 3389) and allowed it in Firewall Packet Filter sections "Internal networks to Zentyal", "External networks to Zentyal", and even "External networks to internal networks".
It's supposed to be working, but it isn't!
Firewall logs show the packets from eth2 to eth0 with source ip of external host and correct destination (ip address of the internal server), decision is REDIRECT. But external host fails to establish the connection!
Where's the problem? Please, help.
P.S. Zetyal 2.0.3 installed from original iso.
Update: I have solved this myself. The problem wasn't actually with Zentyal. Sorry for that little panic.