Port Forwarding some ports works some don't
 

I am working on setting up a firewall to do port forwarding. I am using RH 7.3 and gShield as the firewall script. I currently have port forwarding working for port 3389 and have to get it working for port 5900. I am using the forwards file of gShield and created a rule exactly the same as the one I used for 3389 but for 5900. I can connect to both ports from the servers command prompt using telnet but from outside I can only connect to 3389. Port 5900 is for our vnc program, I have tried changing it to port 6900 which didn't help. Does VNC need any other rules setup like active ftp would or is there any other suggestions on what I can try to help troubleshoot this issue.

Thanks for any and all help
-Scott

P.S. I have just tried forwarding all ports from 3300-6000 and can still only connect to 3389 and not 5900 don't know if this helps.

You could eventually run
...to show how your iptables go

Here is the output of iptables -L -n -t nat

Chain PREROUTING (policy ACCEPT)
target prot opt source destination
DNAT tcp -- 0.0.0.0/0 192.168.7.2 tcp dpts:3300:6900 to:10.0.3.151
DNAT udp -- 0.0.0.0/0 192.168.7.2 udp dpts:3300:6900 to:10.0.3.151

Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
SNAT all -- 10.0.3.0/24 0.0.0.0/0 to:192.168.7.2

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

Does that look right? The 192.168.7.2 is the external NIC the internal nic is 10.3.0.1 and the 10.0.3.151 is the internal server things are being forwarded to.