Hi, thank you for the reply. That bottom image, I just grabbed on the internet, looking for an example of the "Allow Ethernet Clients" checkbox (that I can't seem to find). My stuff is always very current. I haven't seen an Apple UI that looks like that since I had hair.
The version of the AirPort Express I am using is: A1264
(is there another number you were looking for?)
In any case:
<<I would guess that you want to configure it as a wireless Ethernet bridge so that you can connect an Ethernet client to an existing wireless network. Is that correct?>>
Yes, that is correct. I have actually been using the Airport Express like that for about 6-7 years now. But our wifi network's password changed. And I couldn't get into the AirPort Express. So I factory reset it. Connected to it. And, suddenly, the ethernet jack wasn't providing me...well, ethernet. :)
So I looked at the settings, thinking the "Allow Ethernet Clients" checkbox had gotten unchecked in the factory reset, and couldn't find any such checkbox. The Airport Express also said it needed a little update. So I ran that, hoping that might help. Still...no checkbox.
If I was a guessing man, I'd say Apple removed that functionality from the Airport Utility. So I was wondering if anyone else was seeing it, and the problem was somewhere else. Or perhaps that functionality is always on now (hence no checkbox) and the problem is coincidentally somewhere else.