CUPS only creates Xerox printers when AirPrint is enabled

[bdaileyumich]

Hi folks -

I work at a place with a large managed print environment, and for a number of reasons, we leave AirPrint disabled on our devices.

We are finally evaluating IPP Everywhere to handle driver management for our Linux and Mac users, but I'm noticing some inconsistent behavior with how manufacturers have their devices respond to the Get-Printer-Attributes operation, and how CUPS handles the response.

I'm running these tests on an Ubuntu 24.04 machine, CUPS 2.4.7.

For the purposes of this test, I'm using two devices: a Xerox AltaLink C8135 and an HP Color LaserJet Flow X57945.

Xerox Device
With the Xerox device, I ensured IPP is enabled, and AirPrint is disabled. If I try to actually create an IPPE print queue in this state, I get the following response:
PPD creation failed: Printer does not support required IPP attributes or document formats.

Running the Get-Printer-Attributes test via ipptool for this printer reveals that the document-format-supported list does not include image/urf (AirPrint's raster format):
document-format-supported (1setOf mimeMediaType) = application/octet-stream,application/vnd.hp-PCL,text/plain,image/pwg-raster,application/postscript,application/pdf,application/PCLm,image/jpeg,image
/tiff

If I enable AirPrint and rerun the test, image/urf gets added to the list, and I am able to create the IPPE printer.

HP Device
With the HP device, I again ensured IPP is enabled, and AirPrint (and Bonjour) are both disabled. If I try to create an IPPE print queue in this state, it works without issue. Running Get-Printer-Attributes via ipptool in this state returns the following list:
document-format-supported (1setOf mimeMediaType) = text/plain,application/octet-stream,image/jpeg,application/vnd.hp-PCL,application/vnd.hp-PCLXL,application/postscript,application/pdf,image/urf,imag
e/pwg-raster,image/tiff,application/PCLm

So ultimately, my question is this: Which vendor is doing what CUPS/PWG expects? I didn't see anything about this called out in the IPP specification. I can see any argument for either behavior, though obviously in my current situation, I prefer how HP is handling things. Another question would be, is it necessary for CUPS to see the img/urf format supported, when we aren't using AirPrint anyway?

Thanks in advance for your thoughts!

[michaelrsweet]

Apologies for the delay in responding...

WRT printer-specific features that allow for enabling/disabling AirPrint or other "standard" protocols/features, there is no right answer. When enabled, the printer needs to respond as supporting the named protocol or feature (obviously), but since AirPrint, IPP Everywhere, Mopria, and Wi-Fi Direct Print Services all share the same core IPP interface it is possible that for some vendors/printers disabling AirPrint will disable all of the driverless IPP printing features on the printer while another vendor/printer could still support IPP Everywhere, Mopria, etc. which CUPS can use for driverless printing.

So IMHO both printers are "doing the right thing".

There may be ways for you to disable mDNS/DNS-SD on the printers or network so that AirPrint clients will not see the printers on the network and will instead use your CUPS server. That said, if disabling direct printing is important you might want to look at isolating your printers on a separate network/VLAN/etc. that is only accessible from your print server.

[bdaileyumich]

Thanks for the reply Michael! That makes sense. We thankfully already do have our printers on an isolated network - it had slipped my mind that AirPrint, unlike something like Bluetooth, would still require access to the printer via IP address to actually function.