I have cable internet at home but 2 remote office locations setup with DSL.
I have configured routers with Cable/DSL for friends/family so many times I can no longer keep count....simple setup change to move PPP login to router rather than on the modem.
I am in the process of setting up an office location closer to home and ordered DSL service.
The new Motorola 2210 modems (as opposed to the older Speedstream 4100s) now shipping with new ATT DSL service will not work this way.
I tinkered back and forth only to learn that for this model modem you have to set the modem to bridge mode in place of "PPP on Computer" to get it to work.
You still configure PPPoE login in the same way on the router.
Small chance that someone needing this will see it before it scrolls but thought I would pass it along for future use.
YMMV