WRT54GL config. advice please

Question

I am trying to install "Express Talk" soft phone and it is giving me the following message:- >>"A 'Symetric' NAT or router has been detected between this computer and the internet. This means audio cannot be routed to this computer automatically. You are strongly advised to manually set up RTP/UDP redirection at the router or NAT otherwise audio may be delayed, low quality or broken." I checked to manual and the only thing that looks related is the "Filter Internet NAT Redirection" which I have tried "on" & "off" which made no difference, ie still get the same message. Could someone give me some directions please?? Cheers, Phill.

Answer 1

Most standard NAT routers are symmetric NAT. As they try to preserve the port number if possible they may be perceived at times as restricted cone or port restricted cone nat but this will immediately disappear for one computer in the LAN if two computers try to access the same port on the same server in the internet at the same time.
Thus it is pretty much inevitable to configure port forwardings instead. In particular in case you to try access the same internet server from two computers inside the LAN.
You have to configure a static IP address on the computer on which you run the softphone first, e.g 192.168.1.10.
Then forward the ports which the softphone uses. It depends on what you have configured in the softphone. Check the configuration for that. You have to look for the SIP port is listens to (do not confuse this with the SIP port of the service provider) and the RTP ports is uses. With the softphone running you can check the SIP port in a command prompt window. First enter "tasklist" and look the name of the executable of your softphone. Remember the PID number in the second column of that line. Next enter "netstat -aon" and look for the PID in the last column. All lines with the PID in the last column are the SIP ports on which the soft phones listens. If you'll see something like "UDP 0.0.0.0:5060" it means the program listens on port 5060. Take a note of all ports on which the program listens. If in doubt, post the full output of "netstat -aon".
Again, this will only show the SIP ports. It probably won't show the RTP ports as they are allocated during the call. Look through the configuration to find those ports. It has been suggested before that ports 8000-8020 are used for this purpose. But I don't know express talk and the ports can probably be changed in the program.
Now forward all SIP ports and the range of RTP ports to the static IP address of your computer. Always forward UDP. Save the changes.
Next please also verify that your router is directly connected to the internet: click on the Status tab. This will show you the current IP address of the router on the internet port. Then open http://whatismyip.com/ in your browser. It shows your public IP address as seen from the internet. Both IP addresses must be identical. If they are not identical you have another NAT router in your path to the internet. (Often the modem.) Your router is not directly connected to the internet. Configuring port forwarding on your router is futile unless you also configure the same port forwardings on the upstream NAT router.