I'm not sure if this is the place to post this, but figured I'd give it a try.

My router is an ASUS RT-N16 running DD-WRT:
DD-WRT v24-sp2 (11/21/10) big
(SVN revision 15778)

I tried to open a port to permit Windows RDP connections to a laptop on my LAN -- but only to specific remote IP ranges. I have done the following:

1 - Assign static IP to the laptop
I did this under Services->Static leases. I added the MAC address of the laptop and gave it a name and static IP with lease time of 1440 minutes. This appears to work as I can connect using RDP from another machine on my LAN to the laptop using the IP address 192.168.1.X.

2 - Set up a port forward to the laptop
I did this under NAT/QoS->Port Forwarding
I created an entry with these parameters:
Application - RDP
Protocol - Both (although I think only TCP is required)
Source Net - [IP of remote machine...tried my WAN ip and also my entire local subnet 192.168.1.0/24]
Port from - 3389
IP Address - [IP on my LAN of the laptop, 192.168.1.X]
Port to - 3389
Enable - on

I have managed to use these techniques to forward http traffic on port 80 to my linux desktop but can't seem to get remote RDP machines to connect.

I ran nmap on my IP address and it shows the port as open:
Code:
Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2012-06-17 16:42 CDT
Interesting ports on foo.example.com (WWW.XXX.YYY.ZZZ):
Not shown: 1678 filtered ports
PORT     STATE SERVICE
80/tcp   open  http
3389/tcp open  ms-term-serv
I'd like to know if there's any way to check if the traffic is reaching the laptop and the connection refusal is happening there or if I have somehow failed to forward the port. Is there some way to check on the Win XP laptop to see if incoming connections have been refused for some reason?

Any help would be much appreciated.