I've got an ASUS RT-N56U wending its way to me and have been thinking about how to set this up on my home network. I currently have a Netgear DG634g V5 and was hoping to use this device as a modem only, with everything else being done by the router. Problem is, my ISP uses PPPoA and the asus seems only to support PPPoE.

I'm aware that a double NAT configuration should be avoided and I've seen some instructions here:

http://www.tomshardware.co.uk/forum/33700-17-ultimate-modem-router-setup-thread

Specifically, I was going to follow the guidance in the section entitled "Chaining Two Networks Together In a Cascading Fashion (Modem handles PPPoA)". That seems like it could work. However, is this a double NAT configuration or even a good way to do it? Would UPnP still work?

The other option, I understand, is to buy the Draytek Vigor 120 but I'd ideally like to avoid the cost of that if its not necessary.