[FW1] Open ports on Firewall

[Gunjan @ chat4help]

Hi, Is there any way through which we can find out what all ports are open on firewall. Like if Database server is behind the firewall then can we cahek wether port for DB service is open or not.   I already tried nmap to do that, it shows port open on FW m/c but that does not reflect that gave us access to DB server.       Thanks