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I've been using cups network printing with my HP Officejet Pro 8620 for several years. I generally used the cups web interface to set up or modify printers. I set them up as AppSocket/HP JetDirect using port 9100. Typically I've had the same printer set up with 4 different print queues so that I can leave one as single sided black and white, another as double sided color, etc. This worked fine until about a week ago when all four of my 8620 print queues stopped working. I would print to it but nothing would happen. I couldn't even use the web localhost interface to send a test page. The queue would just indicate Idle - "The printer is not responding."
Uninstalling and reinstalling didn't work either. When trying to understand what was wrong I ran across this post,
https://bbs.archlinux.org/viewtopic.php?id=204133
which mentions a way to set it up for port 515 and seems to treat it as equally good as my way with port 9100.
I tried it: lpd setup worked fine and the printers work.
Does anyone know why port 515 might work while 9100 doesn't anymore (but did for years)? I'd rather understand the problem than just move on without understanding because I've found a work around.
Is there some data I should gather and post to help diagnose the problem with the port 9100 setup?
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It could be a package update that has caused it - look through your pacman log and see what was updated "about a week ago".
Have you changed any networking hardware (router for instance ?) or changed any firewall settings?
Following on from the link you posted (into which I originally posted), does "nmap {your printer ip}" show you that port 9100 is open?
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I had the same problem. Fix was adding the port explicitly.
On CUPS webinterface, modify printer:
Changed
socket://192.168.178.89to
socket://192.168.178.89:9100Offline