CUPS and IPP strangeness

CUPS and IPP strangeness

[Dave Close]

I'm managing a small network with about a dozen printers. Some are
unable to accept IPP and are configured to use JetDirect. All others
are configured with IPP.

But one JetDirect printer in particular is having some strangeness.
The /etc/cups/printers.conf file contains these lines.

  <Printer PF0>
  Info HP p2055dn
  DeviceURI socket://pf0

But /var/log/cups/error_log contains lines like this one (wrapped here).

  E [29/Jul/2025:22:03:18 -0700] Returning IPP client-error-bad-request
  for Send-Document (ipp://localhost:631/printers/PF0) from localhost

That sure look to me like CUPS is trying to send IPP traffic to this
printer. That certainly won't work, port 631 is not open on this printer.
I've restarted CUPS without effect. What can I do to fix this?

My major task on this network is to port it to a new system running a
much more recent OS. At this time, CUPS is running on CentOS 6 and is
version cups-1.4.2-81.el6_10.x86_64. I need to keep it running awhile
longer.
-- 
         Dave Close, Compata, Irvine CA       +1 714 434 7359
       dave@compata.com              dhclose@alumni.caltech.edu
  "One thing a person cannot do, no matter how rigorous his analysis
   or heroic his imagination, is to draw up a list of things
   that would never occur to him." -- Thomas Schelling

Re: CUPS and IPP strangeness

[Solomon Peachy]

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On Tue, Jul 29, 2025 at 11:15:40PM -0700, Dave Close wrote:
>   E [29/Jul/2025:22:03:18 -0700] Returning IPP client-error-bad-request
>   for Send-Document (ipp://localhost:631/printers/PF0) from localhost
> 
> That sure look to me like CUPS is trying to send IPP traffic to this
> printer. That certainly won't work, port 631 is not open on this printer.
> I've restarted CUPS without effect. What can I do to fix this?

To me this reads that something sent the _CUPS server_ a "bad" IPP 
request; if it was talking to the printer via JD the URI would include 
the printer's address/name ("pf0") instead of "localhost".

> My major task on this network is to port it to a new system running a
> much more recent OS. At this time, CUPS is running on CentOS 6 and is
> version cups-1.4.2-81.el6_10.x86_64. I need to keep it running awhile
> longer.

I see no reason why you'd need to keep such an old CUPS version around; 
as an example I currently have a CUPS queue talking to a Brother printer 
via JetDirect with CUPS 2.4.x.  It works more reliably than the 
printer's native driverless IPP functionality..

 - Solomon
-- 
Solomon Peachy			      pizza at shaftnet dot org (email&xmpp)
                                      @pizza:shaftnet dot org   (matrix)
Dowling Park, FL                      speachy (libera.chat)

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