I've got a cable modem (A) which is also a wireless router and a dd-wrt wireless router (B).
I've connected (B)'s "internet" port to one of (A)'s local ports.
I can connect to (B) over the air just fine, but when connected, cannot connect to the internet.
Questions like How to bring Internet to a DD-WRT router from another router? seem to indicate I shouldn't have to do anything at all.