Ladysolly wants to be able to print from her various i-things. Once upon a time, she could. But now she couldn't. And since the whole process of printing from an i-thing is shrouded in the obscurity of "it just works" (which doesn't work when it doesn't), I couldn't work out why.
Today, I had a long investigation of this. And I soon saw that althought the IP address of her iPad was 10.149.16.254, the IP address of the Dell printer was 192.168.1.129. And there's no way one would talk to the other.
The IP address of her iPad is set dynamically by DHCP. So, I thought, let's change the IP address of the printer. But how? There's no obvious way. So I googled the printer, and it told me that I could use the setup program on the CD Rom, but that's long gone to goodness-knows-where. I could download the setup program, but first I downloaded the manual, in PDF form. From that, I realised that I could connect to a web server built in to the printer and reconfigure it that way.
So I changed the IP address of one of my computers to 192.168.1.2 (same subnet as the printer) and it was able to view the printer's web page. Good start, but how to change the details? There was a login button, I hit that and it asked for a username and password, which I couldn't remember, of course. So I went to the place where I carefully keep all the million usernames and passwords, and there was the password for the Dell printer.
I logged in to the printer, and changed the IP address from the static 192.168.1.129 to a dynamic one, so that it got the IP address from the router. I immediately lost contact with the printer, but there's a button that lets you print out the printer's info, and that told me that the new address was 169.254.203.109, which sounded pretty random to me, but heigh ho! I changed the computer's IP address to something nearby, and was able to access the printer. And then we tried to print. And it worked!
So now ladysolly can airprint from her i-things to this Dell printer, but only if she's connected to the Wifi that the printer is on, which means that she has to be upstairs to print, which is no great hardship because not even Apple have found a way to get the printed piece of paper from upstairs to downstairs without someone going to fetch it.
And, as a bonus, I can also print to my usual HP printer, as well as the Dell. Which is just as well, because the Dell powers itself off if left alone for a while, and doesn't wake up to print unless you prod a button.