The server was down for a couple of days for reasons unexplained by my hosting provider. I do know that it went down on Saturday night around midnight (or thereabouts), and that they replaced the network interface card. I suspect that when they installed the new card they failed to set up networking properly, so things remained broken until they sorted that out. Then when it did return they still hadn’t set things up properly (it was only binding to one of my IP addresses, and not the one associated with this Web site), so I had to fix it myself.
Have I mentioned that I really am not a systems administrator?