Who'd have thought it? A month ago I was cursing my ADSL modem, on the verge of replacing it for one that actually worked. Instead, I've bought an identical one to install for Mum. Am I really that cruel?
No, I just figured out how to make it work. (And someone at work was flogging one on the cheap.)
The rest of this is just techie detail for anyone similarly struggling. Non-techies, look away now.
The D-Link DSL-300G+ is a good product if you want to connect just one machine to the Internet, but if you try to plug it into an Apple AirPort Base Station you'll be tearing your hair out in no time.
The problem seems to be that while the AirPort Base Station correctly obtains an IP address from the ADSL modem, it doesn't pick up a default route and so doesn't know what to do with IP packets coming in from the wireless clients.
Here's the fix.
In the UK most ADSL modems are set up to talk PPPoA. It turns out that BT now supports PPPoE on its ADSL lines, and that's something the AirPort Base Station can talk too; we just need a device to convert the ATM signal on your ADSL line into Ethernet: an RFC 1483 bridge. The DSL-300G+ can work in such a mode.
And you're away! I hope that helps anyone struggling with the same problem.
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