I suppose I should say right from the start that this story probably isn’t the standard 10.7 connection problem you’ll read about all over the net. This solution may help some people, though. This post also acts as a kind of addendum to this one, about general technology malaise at Rosam Towers.

When I upgraded my late 2010 MacBook Air to OS X 10.7 Lion just a few days after it launched, everything was fine. So fine that I upgraded my iMac, too.

Somewhere along the line, the Air started having problems with connecting to my wi-fi, and occasionally the iMac, as well. I upgraded Lion immediately updates became available, but the problems continued, so that I needed to reboot the Air, and increasingly the Apple AirPort Extreme.

Then I started getting an error message – just now and then – that there was already a device on the IP address that had been assigned to the Air as it reconnected. The penny dropped. Over a year ago, when we upgraded to 50Mbit/sec broadband, Virgin had installed a new wireless router in place of the cable modem we had previously.

Loathe to substitute a ‘free’ ISP wireless router for my AirPort Extreme, and to spend time reconfiguring the network, I first tried plugging the Extreme into the Virgin router. I ‘knew’ this wouldn’t work because I’d then have two DHCP servers on the network, but I could switch one off, couldn’t I?

The thing was, the network worked immediately, without any further messing, and continued to work with no problems at all until Lion turned up.

Once I’d remembered I had two DHCP servers in the network, I decided that the simplest way to get it all working was to remove the Extreme and reconfigure the Virgin router with the same network name and password as the Extreme.

That was more than two weeks ago, and there has not been a single network problem from any device on the network. Lion doesn’t like having two DHCP servers on the network, unlike Leopard, Snow Leopard, iPhone, iPad, iPod Touch or Apple TV.