Can not port forward on WRT54GS v6 "You cannot use the router IP"

Question

Hello, I'm trying to open a port number, but when I try to use my router's IP, the following message appears
 "You cannot use the router IP, network, or broadband address"
[IMG]http://i45.tinypic.com/107qond.jpg[/IMG]
My ADSL was working as a NAT behind a NAT connection, so I had to change my Local IP Address to 192.168.2.1.
Router: WRT54GS v6 firmware 1.52.8 (latest)  -  Bellsouth router: Westell 6100
Microsoft Windows [Version 6.1.7600]
Ethernet adapter Local Area Connection:
   Connection-specific DNS Suffix  . : launchmodem.com
   Link-local IPv6 Address . . . . . : fe80::40a9:a76e:61b3:6435%11
   IPv4 Address. . . . . . . . . . . : 192.168.2.100
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.2.1
So, please help me, how can I open ports on my router? =[
PS: I tried to use 192.168.2.100, and even though it lets me use it, it still seems not to open that port... my IP is dynamic.

Answer 1

Generally: NAT behind NAT is a bad idea. There is usually no need for double NAT. Either configure the ADSL router as bridge and use the WRT for your internet connection or set up the WRT as simple access point behind the ADSL router.
It's also unclear to me what is working or not. First I thought you can't set up forwarding at all because you get that error message. Then, in your PS you write you tried to use 192.168.2.100 and that seemed to be possible. The IP address to forward to must be the IP address of the computer to which you want to forward. Thus 192.168.2.100 is exactly the IP address you have to set up. Does this work or not?
Also remember: with double NAT you must set up two forwardings: first on the ADSL router then on the WRT. Port forwarding is necessary to allow incoming traffic through NAT. All incoming traffic arrives on the ADSL router. Thus setting up port forwarding on the WRT only won't do a thing.
It's also not recommend to use dynamic IPs for forwarding destinations. Dynamic IP addresses may change over time and that requires you to adjust forwardings accordingly. It's better to reserve fixed IP addresses (if your WRT supports this) or set a static IP address on the computer outside the DHCP address pool.