Quote Originally Posted by ctaranto View Post
With modem -> router -> ATA, how does one get single NAT? Turning NAT off on the RT makes it not get Phone 1 lit.

And where are my "4 NATs"? Not knowing what happens internally, I believe that having the RT entirely on the 172.20.0 network, it's not doing NAT at all. I thought NAT happens when going from 172 to 192, or public to private.

-Craig
Assuming your modem is bridged, there's only one IP change from your public IP through your DHCP router to ATA ......thus single NAT.

If your ATA is attached directly to a bridged modem, there's no NAT at all since the ATA is seeing your public IP. Only the device's attached to the LAN port of the RT31P2 experience NAT.

My apologies, it looks like there is less than 4 NAT's since you turned off the DHCP server in the RT31P2. I'd have to study your setup a little closer to get a better idea of how many NAT's are going on.

There's still a problem somewhere in your setup if you are having to go to this trouble.