I'm trying to get a very old, but working great C2001A/J4100A (HP LaserJet 4) to work with the HP Linux Imaging and Printing library, but I'm having an awful time of it.
1) There's no entry in /usr/share/hplip/data/models/models.dat for [hp_laserjet_4]. This is the first problem so far when I used Bonjour discovery through an avahi.service file I put on my OpenWRT router. I don't currently have an iPhone I want it to discover with AirPrint, but this is how I started off and helps CUPS finds printers anyways.
2) SLP discovery is a complete bomb. I've traced it down to the UDP packet the JetDirect sends off in response to the broadcast discovery request. The part that is 'x-hp-p1=0' should be something like 'x-hp-p1=MFG:HP;MDL:LaserJet4;etc..' and it causes hp-probe to fail to see what printer the JetDirect is plugged into.
I can't seem to force HPLIP to bypass the bad discovery methods and it's too smart and wants to verify.
I've posted to the HPLIP help area, but they seem to run a week slow.
Instead of doing JetDirect, try LPR directly to the IP address. And any of the older PCL drivers should work against that printer.