I’m guessing that 2Wire sent another firmware update without notification and it messed-up the DHCP settings.
It appeared that everything was good on the 2Wire side, because I could plug my laptop in directly and it worked fine. That inferred that the problem was with a downstream router (I utilize a “router-behind-a-router” network to reduce domain collisions and increase security), so I performed a power cycle on the unit, and when that failed to correct the issue, did a Factory Reset. It still didn’t work, so I plugged in a spare router, still nada. This was good evidence that the upstream 2Wire really was the cause of the problem.
So I went back to the 2Wire router and looked around. Then I saw it: the DHCP Mask, which is usually 255.255.255.0. But on the 2Wire, it was 255.255.252.0. Doh!
AT&T seems to be mucking around with my customized settings….