http://www.dd-wrt.com/wiki/index.php/Default_internal_device_networks
http://wiki.openwrt.org/toh/asus/rt-n16#specific.configuration
http://www.christopherkois.com/?p=497
I had looked this (or something like it) up not that long ago as I wanted to do some VLAN trunking through my Asus RT-N16, and I managed to lose it before getting it implemented. It took a little bit of digging, but I think this got me back to a good starting point at least.
My plan is to trunk several networks from my basement up to a manged switch upstairs, from which I will support a second WAN router for a test network as well as an internal 5GHz wireless network , and possibly some additional internal segmented networks. I have quite some distance to go to accomplish this yet, but at least now I have the base reference to the physical/internal port mappings again. That’s an hour and a half I won’t have to spend next time.