Re: Difference between ipp, ipps, http, https CUPS protocols?

[Kent West]

On 11/17/19 3:02 AM, Anthony DeRobertis wrote:
Quick search of 
https://sources.debian.org/src/cups/2.3.0-7/backend/ipp.c/ shows there 
is no different between ipp and http, and no difference between ipps 
and https.


ipps and https force encryption, using SSL/TLS (just like you'd expect 
from https) (so if your printer doesn't offer encryption, say due to 
no certificates, it'll fail).


ipp and http do not require encryption (but may use it anyway, if 
available, via a TLS upgrade).


Probably CUPS offers both because some printers' documentation gives 
http:// URLs and some give ipp:// URLs.




Thank you! Good information!


--

Kent

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Anthony DeRobertis]

Quick search of 
https://sources.debian.org/src/cups/2.3.0-7/backend/ipp.c/ shows there 
is no different between ipp and http, and no difference between ipps and 
https.


ipps and https force encryption, using SSL/TLS (just like you'd expect 
from https) (so if your printer doesn't offer encryption, say due to no 
certificates, it'll fail).


ipp and http do not require encryption (but may use it anyway, if 
available, via a TLS upgrade).


Probably CUPS offers both because some printers' documentation gives 
http:// URLs and some give ipp:// URLs.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Fri 15 Nov 2019 at 12:44:16 -, Dan Purgert wrote:

> mick crane wrote:
> > On 2019-11-14 23:52, Dan Purgert wrote:
> >
> >>> What is more interesting is why a user thinks that the LPD protocol
> >>> gives them something that IPP doesn't.
> >> 
> >> Who said that LPR/LPD gave people "something" that IPP doesn't?

My musing could be seen as a question exploring whether the LPD
protocol has any advantages over the IPP protocol.

> > I'm not really sure about what happens.
> > Is it that a CUPS server translates what it receives from client to
> > sequence of instructions printer understands ?
> > Certain on client
> >
> > " mytext | lpr "
> >
> > worked, which could be handy.
> 
> Yeah, CUPS does provide hooks for some commands (similarly to how say
> postfix or exim provide 'sendmail(tm)').
> 
> This entire discourse between Brian and myself started with a question
> to the effect of "what will 'we' (presumably 'Dan' and 'Brian') do

The "we" was intended to encompass all users of the Debian printing
system.

> if/when CUPS removes PPD support for our old printers?" ( MID
>  ).  I responded with a crack about LPRng
> being the "solution" to continue supporting the old stuff (and, in the
> case of 'new stuff' that still supports the old LPR/LPD protocols; why
> bother mucking around with changes I don't "need" to make).

There is no "if" about? When? After CUPS 2.3. A couple of years?

-- 
Brian.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

mick crane wrote:
> On 2019-11-14 23:52, Dan Purgert wrote:
>
>>> What is more interesting is why a user thinks that the LPD protocol
>>> gives them something that IPP doesn't.
>> 
>> Who said that LPR/LPD gave people "something" that IPP doesn't?
>
> I'm not really sure about what happens.
> Is it that a CUPS server translates what it receives from client to
> sequence of instructions printer understands ?
> Certain on client
>
> " mytext | lpr "
>
> worked, which could be handy.

Yeah, CUPS does provide hooks for some commands (similarly to how say
postfix or exim provide 'sendmail(tm)').

This entire discourse between Brian and myself started with a question
to the effect of "what will 'we' (presumably 'Dan' and 'Brian') do
if/when CUPS removes PPD support for our old printers?" ( MID
 ).  I responded with a crack about LPRng
being the "solution" to continue supporting the old stuff (and, in the
case of 'new stuff' that still supports the old LPR/LPD protocols; why
bother mucking around with changes I don't "need" to make).

I've so far never been a proponent of X over Y (excepting plaintext IPP
over trying to set up SSL/TLS on your printer for IPPS).

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Re: Difference between ipp, ipps, http, https CUPS protocols?

[mick crane]

On 2019-11-14 23:52, Dan Purgert wrote:


What is more interesting is why a user thinks that the LPD protocol
gives them something that IPP doesn't.


Who said that LPR/LPD gave people "something" that IPP doesn't?


I'm not really sure about what happens.
Is it that a CUPS server translates what it receives from client to
sequence of instructions printer understands ?
Certain on client

" mytext | lpr "

worked, which could be handy.

mick



--
Key ID4BFEBB31

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

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Hash: SHA256

Brian wrote:
> On Thu 14 Nov 2019 at 11:12:38 -, Dan Purgert wrote:
>> Sorting by "newest" on their (laser / color led) models listing results
>> in the "HL-L3270CDW" being listed as "newest" -- digging around, it
>> seems that it's a 2018 model.  Still has LPR/LPD listed under the
>> "Protocols" sections (both IPv4 and v6, actually).
>> 
>> I would expect that pretty much everything of theirs (well, at least in
>> terms of "business lineup") would then still support it. Their site
>> seems a bit broken right now (or perhaps it's on my end), so I can't get
>> at the 'home' stuff to check.
>
> One would think that a business machine supporting the LPD protocol
> would cost a vendor pennies. After all, the vendor doesn't have to
> do much when they already have the code to put in their firmware.

Yup, if that.  

>
> What is more interesting is why a user thinks that the LPD protocol
> gives them something that IPP doesn't.

Who said that LPR/LPD gave people "something" that IPP doesn't?



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Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Thu 14 Nov 2019 at 11:12:38 -, Dan Purgert wrote:

> Brian wrote:
> > I wonder how many modern printers support the lpd protocol?
> 
> How do we define "modern"?  Just looked at a few Brother MFPs, and they
> still support it (although I don't know how old the actual models are).

Modern? I'd say something sold in the past 5/10 years that supports
AirPrint.

> Sorting by "newest" on their (laser / color led) models listing results
> in the "HL-L3270CDW" being listed as "newest" -- digging around, it
> seems that it's a 2018 model.  Still has LPR/LPD listed under the
> "Protocols" sections (both IPv4 and v6, actually).
> 
> I would expect that pretty much everything of theirs (well, at least in
> terms of "business lineup") would then still support it. Their site
> seems a bit broken right now (or perhaps it's on my end), so I can't get
> at the 'home' stuff to check.

One would think that a business machine supporting the LPD protocol
would cost a vendor pennies. After all, the vendor doesn't have to
do much when they already have the code to put in their firmware.

What is more interesting is why a user thinks that the LPD protocol
gives them something that IPP doesn't.

-- 
Brian.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

Brian wrote:
> On Wed 13 Nov 2019 at 13:55:57 -, Dan Purgert wrote:
>> You asked about the "classic" printers we both (apparently) own.  Mine
>> here still support being addressed via LPR/LPD, not to mention PCL,
>> postscript, etc.
>
> I wish I hadn't been so disparaging about about LPRng. People should be
> able to use what they want to use, and, if LPRng fits, why not? OTOH,
> it is unable to do what a modern CUPS system can do and does not offer
> what many users want, particularly when it comes to easy setup.

Sure, CUPS does make it comparatively easy for "Joe Average" ... I've
found things to be about on-par when you're talking about small offices
though; where the print-jobs are pretty boring/standard (all text, all
b, all 2-sided, etc.). 

LPR/LPD needs a little extra setup at first, but then "just runs".

CUPS doesn't take as long to setup, but does require an hour or two
every few months to keep behaving ... but then again, those two sites
are also the busiest in terms of printing; so maybe that plays into it.

> [...]
> I wonder how many modern printers support the lpd protocol?

How do we define "modern"?  Just looked at a few Brother MFPs, and they
still support it (although I don't know how old the actual models are).

Sorting by "newest" on their (laser / color led) models listing results
in the "HL-L3270CDW" being listed as "newest" -- digging around, it
seems that it's a 2018 model.  Still has LPR/LPD listed under the
"Protocols" sections (both IPv4 and v6, actually).

I would expect that pretty much everything of theirs (well, at least in
terms of "business lineup") would then still support it. Their site
seems a bit broken right now (or perhaps it's on my end), so I can't get
at the 'home' stuff to check.


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Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Wed 13 Nov 2019 at 13:55:57 -, Dan Purgert wrote:

> -BEGIN PGP SIGNED MESSAGE-
> Hash: SHA256
> 
> Brian wrote:
> > On Tue 12 Nov 2019 at 20:27:00 -, Dan Purgert wrote:
> >
> >> Brian wrote:
> >> >> 
> >> >> Not really, tbh.  I haven't had to look that deeply into the state of
> >> >> printing in ... well, much longer than I thought it'd been this morning.
> >> >> 
> >> >> Time flies :| 
> >> >
> >> > So, when CUPS ceases to support PPDs (probably in a couple of years),
> >> > your and mine classic printers will cease to work. Is there a magic
> >> > wand someone can wave?
> >> 
> >> LPRng? :)
> >
> > A clapped-out, unsupported and ancient printing system. That's
> > going to go down well with users in 2019.
> 
> You asked about the "classic" printers we both (apparently) own.  Mine
> here still support being addressed via LPR/LPD, not to mention PCL,
> postscript, etc.

I wish I hadn't been so disparaging about about LPRng. People should be
able to use what they want to use, and, if LPRng fits, why not? OTOH,
it is unable to do what a modern CUPS system can do and does not offer
what many users want, particularly when it comes to easy setup.

> Can't speak for your users, but mine don't know their print jobs are
> (still) backed by LPD/LPR.  But then again, they don't notice much
> beyond "does facebook work today".  Good people, just not the most
> technical.

I wonder how many modern printers support the lpd protocol?

-- 
Brian.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

Brian wrote:
> On Tue 12 Nov 2019 at 20:27:00 -, Dan Purgert wrote:
>
>> Brian wrote:
>> >> 
>> >> Not really, tbh.  I haven't had to look that deeply into the state of
>> >> printing in ... well, much longer than I thought it'd been this morning.
>> >> 
>> >> Time flies :| 
>> >
>> > So, when CUPS ceases to support PPDs (probably in a couple of years),
>> > your and mine classic printers will cease to work. Is there a magic
>> > wand someone can wave?
>> 
>> LPRng? :)
>
> A clapped-out, unsupported and ancient printing system. That's
> going to go down well with users in 2019.

You asked about the "classic" printers we both (apparently) own.  Mine
here still support being addressed via LPR/LPD, not to mention PCL,
postscript, etc.

Can't speak for your users, but mine don't know their print jobs are
(still) backed by LPD/LPR.  But then again, they don't notice much
beyond "does facebook work today".  Good people, just not the most
technical.


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Re: Difference between ipp, ipps, http, https CUPS protocols?

[Gene Heskett]

On Tuesday 12 November 2019 11:01:39 Klaus Singvogel wrote:

> Gene Heskett wrote:
> > > CreateProfile failed:
> > > org.freedesktop.ColorManager.AlreadyExists:profile ... already
> > > exists
> >
> > Thats permissions.. But why can't the same software that wrote that
> > profile, rewrite that profile?
>
> Ask the software developer, which I'm not.
>
> > So what do I do to get admin writes, including overwriting the
> > edited ppd or whatever when there is no root pw, only sudo.
>
> ever did: sudo su
Thats not scripted in the permissions user/pw the admin menu presents.

> > So if its complaining it can't overwrite the file, when its the
> > exact same sw that wrote it three days back up the log.

And you are mixing instantly generated logs with old logs, what I'm 
seeing is generated and logged when the modify printer button at the 
bottom of the firefox screen is clicked.
> No, the regular rotated logfile shows the error in the logfile three
> days ago. But I think this happened more often - in older logfiles.

No argument there, with the log blossoming in no permission reports as I 
try to print a linuxcnc config file I want to modify for better machine 
performance. So I get curious a week ago and find I am now denied, no 
permission, from a machine that worked 4 weeks back. The list now 
includes the buster-10.1 install on the rpi4, and all 3 of the wheezy's 
that run my machinery, and they haven't been updated of anything but 
linuxcnc since wheezy support ended.  The key I feel is the install of 
stretch and subsequent updates on this machine. I've had screaming good 
luck building a realtime kernel for the rpi4, runs smoothly at very low 
latency's and I want that to be propagated to other users, but its a 
built kernel=2.5G, which someone is pulling right now.  But the instant 
thats done, I'll be watching the logs and playing whackamole with the 
bots until I've stopped them again.

In the meantime I need to learn how to save those rules and restart 
iptables fully armed at reboot time. But the man page might as well be 
in swahili.

So two things: 

1: How do I save what I have applied already in a reloadable format?

2: how do I restart it at boot time fully armed with those saved rules.

> Best regars,
>   Klaus.

It all worked, for a few days after the stretch install, say till 
synaptic brought it all uptodate, then its gone to hell in a handbasket 
since.

Should I reach around the FF interface with a sudo -i login shell and 
delete all references to that printer in the /etc/cups directory tree 
just before clicking on modify printer the last time? Will that get 
around the no permissions problem? This is after all software, and it 
can be fixed but probably not forever since somebodies paranoia will see 
to it that fix route is blocked eventually. I'd much druther make your 
way work. Currently that doesn't seem possible with the tooling 
provided. But I'd be delighted to be proven wrong. Its certainly holding 
up progress here.

Thank you Klaus.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Tue 12 Nov 2019 at 20:27:00 -, Dan Purgert wrote:

> Brian wrote:
> >> 
> >> Not really, tbh.  I haven't had to look that deeply into the state of
> >> printing in ... well, much longer than I thought it'd been this morning.
> >> 
> >> Time flies :| 
> >
> > So, when CUPS ceases to support PPDs (probably in a couple of years),
> > your and mine classic printers will cease to work. Is there a magic
> > wand someone can wave?
> 
> LPRng? :)

A clapped-out, unsupported and ancient printing system. That's
going to go down well with users in 2019.

-- 
Brian

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

Brian wrote:
>> 
>> Not really, tbh.  I haven't had to look that deeply into the state of
>> printing in ... well, much longer than I thought it'd been this morning.
>> 
>> Time flies :| 
>
> So, when CUPS ceases to support PPDs (probably in a couple of years),
> your and mine classic printers will cease to work. Is there a magic
> wand someone can wave?

LPRng? :)


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Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Tue 12 Nov 2019 at 19:51:42 -, Dan Purgert wrote:

> Brian wrote:
> > On Tue 12 Nov 2019 at 11:30:33 -, Dan Purgert wrote:
> >
> >> I believe the newest printers offer a way to print "driverless" via IPP
> >
> > "Newest" encompasses the past 5-10 years.
> 
> Yeah, meant "newer" there.  Have had my current lasers longer than that,
> so ... :/
> 
> >
> >> told it via the control channel gets you a nice document.  Though, that
> >> might just be vaporware at the moment.
> >
> > Vaporware? Are you aware of the effort put in by upstream CUPS and
> > cups-filters to support modern printers? Driverless printing is a
> > reality now and is the future.
> 
> Not really, tbh.  I haven't had to look that deeply into the state of
> printing in ... well, much longer than I thought it'd been this morning.
> 
> Time flies :| 

So, when CUPS ceases to support PPDs (probably in a couple of years),
your and mine classic printers will cease to work. Is there a magic
wand someone can wave?

-- 
Brian.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

Brian wrote:
> On Tue 12 Nov 2019 at 11:30:33 -, Dan Purgert wrote:
>
>> I believe the newest printers offer a way to print "driverless" via IPP
>
> "Newest" encompasses the past 5-10 years.

Yeah, meant "newer" there.  Have had my current lasers longer than that,
so ... :/

>
>> told it via the control channel gets you a nice document.  Though, that
>> might just be vaporware at the moment.
>
> Vaporware? Are you aware of the effort put in by upstream CUPS and
> cups-filters to support modern printers? Driverless printing is a
> reality now and is the future.

Not really, tbh.  I haven't had to look that deeply into the state of
printing in ... well, much longer than I thought it'd been this morning.

Time flies :| 
>


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Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Tue 12 Nov 2019 at 11:30:33 -, Dan Purgert wrote:

> I believe the newest printers offer a way to print "driverless" via IPP

"Newest" encompasses the past 5-10 years.

> as well -- that is, rather than needing a device-specific PPD, the use
> of IPP lets you just send a standardized "printing format" (PDF, PCL,
> something like that), and that "printing format" plus the options you

PDLS are PDF, Apple Raster and PWG Raster. pclm too (but that is not
PCL).

> told it via the control channel gets you a nice document.  Though, that
> might just be vaporware at the moment.

Vaporware? Are you aware of the effort put in by upstream CUPS and
cups-filters to support modern printers? Driverless printing is a
reality now and is the future.

-- 
Brian.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Gene Heskett]

On Tuesday 12 November 2019 10:15:33 David Wright wrote:

> On Tue 12 Nov 2019 at 09:26:03 (-0500), Gene Heskett wrote:
> > On Tuesday 12 November 2019 08:48:41 Klaus Singvogel wrote:
> > > Gene Heskett wrote:
> > > > That [v1.::1] looks like shorthand for ipv6, but the nearest
> > > > ipv6 capable connection is probably 185 miles north of here in
> > > > Pittsburgh PA. There is not AFAIK, any ipv6 provisioned anyplace
> > > > on my local ISP the local cable folks
> > >
> > > Forget this. This message is hours away from your real issue.
> > >
> > > Most proably caused by a "Listen [v1.::1]:631" entry in
> > > /etc/cups/cupsd.conf
> >
> > is
> > Listen localhost:631
>
> And a conventional installation would show:
>
> $ grep localhost /etc/hosts
> 127.0.0.1  localhost
>
> ::1localhost ip6-localhost ip6-loopback
>
> $
>
> but has that been nuked?
>
Yes, no trace of ipv6 stuff. its all been commented out:
127.0.0.1   localhost
192.168.71.1router.coyote.den   router
192.168.71.3coyote.coyote.den   coyote
192.168.71.4shop.coyote.den shop
192.168.71.5lathe.coyote.denlathe
192.168.71.6lappy.coyote.denlappy
192.168.71.7vna.coyote.den  vna
192.168.71.10   GO704.coyote.denGO704
192.168.71.2rock64.coyote.den   rock64
192.168.71.12   picnc.coyote.denpicnc
192.168.71.13   rpi4.coyote.den rpi4
192.168.71.21   scanner.coyote.den  scanner
192.168.71.30   redpitaya.coyote.denred
# The following lines are desirable for IPv6 capable hosts
#::1 localhost ip6-localhost ip6-loopback
#ff02::1 ip6-allnodes
#ff02::2 ip6-allrouters
# the following may be dns blacklisted,due to a lawsuit, so
31.184.194.81 Sci-Hub


> Cheers,
> David.

If cups is looking for ipv6 stuff, I don't intend to allow it to find it. 
Any time an ipv6 capability is found, route flat refuses to use a legal 
ipv4 address and I cannot get off the property.  This bit of having ipv6 
everwhere, when the nearest ipv6 connectivity is 100 + mile away is the 
biggest pain in the ass ever about doing a modern os install.  It took 
me  wholesale removal of avahi-* and dhcphd to get a working network 
when I install stretch on anything because with them installed, route 
insisted my gateway was the 169 shit ahahi assigned.  Avahi is, in my 
opinion, a plant from microsoft to screw up linux. Get rid of it with 
prejudice.

I have one buster 10.1 install, from raspbian, and knowing what it took 
to get networking, to just work, that stuff got removed from its sd card 
boot image before it was plugged in and booted the first time, and it 
all Just Works.

But thats not fixing my cups install. So lets do that. Its seems obvious 
I've a perms problem but where is it? To repeat, there is not a root 
password, never been set, and man vi doesn't even tell you how to exit 
visudo which I used to view the contents of sudoers. I have used vi/vim 
but that was 20 years ago and I found many far more convenient editors 
since.  So I guess another reboot to get rid of visudo is coming up.  
Except that will interrupt a download ahh no it won't, the ddos is back 
because an earlier reboot canceled all my iptabes rules. And semrush et 
all is downloading my whole site again and again. usng up all my upload 
bandwidth. I'll be back, when I have regained control of my website.


Thanks David

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Kent West]

On 11/12/19 9:02 AM, Brian wrote:

On Mon 11 Nov 2019 at 10:18:26 -0600, Kent West wrote:

When adding a printer via the CUPS web interface (localhost:631) on my
Debian box, Administration / Add Printer / Other Network Printers,
there are
four Internet Printing Protocol options:

https

ipp

http

ipps

Which one do I want to select? What are the differences?

Essentially, use ipp unless you have a good reason not to.


^

This is the information I needed, which (IMO) should have been on the 
CUPS setup page.




Not quite. Both ipp and ipps do encryption. The difference is that ipp
does oportunistic encryption (using an http upgrade) whereas, with ipps,
encryption is always on (the encryption is immediate, using https). The
rationale for having a ipps URI is in RFC7472.

http is the transport protocol for ipp and ipps, and ipp and ipps URIs
are mapped to http and https URLs. Every modern printer would support
ipp; in addition, some could support ipps too. I believe the http and
https backends exist to facilitate connections with Windows machines,
which historically have lagged far behind in implementing ipp.



And this information helps, too.

Thanks!


--

Kent

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Klaus Singvogel]

Gene Heskett wrote:
> > CreateProfile failed:
> > org.freedesktop.ColorManager.AlreadyExists:profile ... already exists
> >
> Thats permissions.. But why can't the same software that wrote that 
> profile, rewrite that profile?

Ask the software developer, which I'm not.

> So what do I do to get admin writes, including overwriting the 
> edited ppd or whatever when there is no root pw, only sudo.

ever did: sudo su

> So if its complaining it can't overwrite the file, when its the exact 
> same sw that wrote it three days back up the log.

No, the regular rotated logfile shows the error in the logfile three days
ago. But I think this happened more often - in older logfiles.

Best regars,
Klaus.
-- 
Klaus Singvogel
GnuPG-Key-ID: 1024R/5068792D  1994-06-27

Re: Difference between ipp, ipps, http, https CUPS protocols?

[David Wright]

On Tue 12 Nov 2019 at 09:26:03 (-0500), Gene Heskett wrote:
> On Tuesday 12 November 2019 08:48:41 Klaus Singvogel wrote:
> > Gene Heskett wrote:
> > > That [v1.::1] looks like shorthand for ipv6, but the nearest ipv6
> > > capable connection is probably 185 miles north of here in Pittsburgh
> > > PA. There is not AFAIK, any ipv6 provisioned anyplace on my local
> > > ISP the local cable folks
> >
> > Forget this. This message is hours away from your real issue.
> >
> > Most proably caused by a "Listen [v1.::1]:631" entry in
> > /etc/cups/cupsd.conf
> is
> Listen localhost:631

And a conventional installation would show:

$ grep localhost /etc/hosts
127.0.0.1  localhost
::1localhost ip6-localhost ip6-loopback
$ 

but has that been nuked?

Cheers,
David.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Tue 12 Nov 2019 at 08:46:50 +1300, Richard Hector wrote:

> On 12/11/19 8:38 AM, Kent West wrote:
> > 
> > On 11/11/19 10:40 AM, Brian wrote:
> >> On Mon 11 Nov 2019 at 10:18:26 -0600, Kent West wrote:
> >>
> >>> Probably answered somewhere, but I've been DuckDuckGo-ing for the
> >>> past two
> >>> hours and can't find the answer.
> >>>
> >>> When adding a printer via the CUPS web interface (localhost:631) on my
> >>> Debian box, Administration / Add Printer / Other Network Printers,
> >>> there are
> >>> four Internet Printing Protocol options:
> >>>
> >>> https
> >>>
> >>> ipp
> >>>
> >>> http
> >>>
> >>> ipps
> >>>
> >>> Which one do I want to select? What are the differences?
> >> 'ls -l /usr/lib/cups/backend' tells you that it doesn't matter what
> >> choice you make.
> >>
> > 
> > lrwxrwxrwx 1 root root  3 Oct 31 02:44 http -> ipp
> > lrwxrwxrwx 1 root root  3 Oct 31 02:44 https -> ipp
> > -rwxr-xr-x 1 root root  80120 Oct 31 02:44 ipp
> > lrwxrwxrwx 1 root root  3 Oct 31 02:44 ipps -> ipp
> > 
> > Thank you. That does tell me they are all the same.
> 
> It doesn't tell me that.

I've come round to your way of thinking.

> It tells me that they're all the same file, but an executable can find
> out what name it was called with, and change its behaviour accordingly.
> Busybox is an extreme example.

That went through my mind at the time, but I went for the easy (and not
quite correct) response to keep things simple. Essentially, use ipp
unless you have a good reason not to.

> > It does not tell me
> > why CUPS on Debian makes the other three options available (thereby
> > confusing the person adding the printer). There must be some reason why
> > a person would expect to choose X over Y; that's the difference I'm
> > looking for.
> > 
> > But your answer certainly helps. I now know it doesn't matter which of
> > these I select.
> 
> I would guess that the *s versions use TLS, but beyond that I don't
> know. I'd agree with deloptes that it probably depends on what the
> remote end can support.

Not quite. Both ipp and ipps do encryption. The difference is that ipp
does oportunistic encryption (using an http upgrade) whereas, with ipps,
encryption is always on (the encryption is immediate, using https). The
rationale for having a ipps URI is in RFC7472.

http is the transport protocol for ipp and ipps, and ipp and ipps URIs
are mapped to http and https URLs. Every modern printer would support
ipp; in addition, some could support ipps too. I believe the http and
https backends exist to facilitate connections with Windows machines,
which historically have lagged far behind in implementing ipp.

-- 
Brian.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Gene Heskett]

On Tuesday 12 November 2019 09:11:04 Curt wrote:

> On 2019-11-12, Klaus Singvogel  wrote:
> > CreateProfile failed:
> > org.freedesktop.ColorManager.AlreadyExists:profile ... already
> > exists
>
> Maybe as simple as "Resume Printer" (wouldn't that be wonderful?).
>
Except there is no place advising printer is paused,
> > Best regars,
> > Klaus.


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Gene Heskett]

On Tuesday 12 November 2019 08:48:41 Klaus Singvogel wrote:

> Gene Heskett wrote:
> > This is my logs:
> > root@coyote:cups$ cat /var/log/cups/access_log
> > localhost - - [12/Nov/2019:00:11:00 -0500] "POST / HTTP/1.1" 200 349
> > Create-Printer-Subscriptions successful-ok localhost - -
> > [12/Nov/2019:00:11:00 -0500] "POST / HTTP/1.1" 200 176
> > Create-Printer-Subscriptions successful-ok root@coyote:cups$ cat
> > /var/log/cups/error_log.1
> > E [11/Nov/2019:00:10:25 -0500] Unable to open listen socket for
> > address [v1.::1]:631 - Cannot assign requested address. E
> > [11/Nov/2019:16:16:00 -0500] [cups-deviced] PID 22513
> > (gutenprint52+usb) stopped with status 1! E [11/Nov/2019:16:16:00
> > -0500] [cups-deviced] PID 22511 (begonia) stopped with status 1! W
> > [11/Nov/2019:16:18:17 -0500] CreateProfile failed:
> > org.freedesktop.ColorManager.AlreadyExists:profile id
> > \'Brother_HL-2140_series-Gray..\' already exists
> > E [11/Nov/2019:16:18:45 -0500] [cups-deviced] PID 22693 (begonia)
> > stopped with status 1! E [11/Nov/2019:16:18:45 -0500] [cups-deviced]
> > PID 22695 (gutenprint52+usb) stopped with status 1! W
> > [11/Nov/2019:16:20:12 -0500] CreateProfile failed:
> > org.freedesktop.ColorManager.AlreadyExists:profile id
> > \'Brother_HL-2140_series-Gray..\' already exists
> >
> > That [v1.::1] looks like shorthand for ipv6, but the nearest ipv6
> > capable connection is probably 185 miles north of here in Pittsburgh
> > PA. There is not AFAIK, any ipv6 provisioned anyplace on my local
> > ISP the local cable folks
>
> Forget this. This message is hours away from your real issue.
>
> Most proably caused by a "Listen [v1.::1]:631" entry in
> /etc/cups/cupsd.conf
is
Listen localhost:631

> > So thats probably the first thing to fix, but where is it?
>
> No, forget this. Put your focus on that error message:
>
> CreateProfile failed:
> org.freedesktop.ColorManager.AlreadyExists:profile ... already exists
>
Thats permissions.. But why can't the same software that wrote that 
profile, rewrite that profile?  I'm in sudoers. Looking for perms to 
admin this presents a requester with root filled and a password about a 
week long, which I change me me and my password so sudo will work, there 
is no root pw on any of my machines, and does not complain until the 
log.  So what do I do to get admin writes, including overwriting the 
edited ppd or whatever when there is no root pw, only sudo.
So if its complaining it can't overwrite the file, when its the exact 
same sw that wrote it three days back up the log.

> Best regars,
>   Klaus.


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Curt]

On 2019-11-12, Klaus Singvogel  wrote:
>
> CreateProfile failed: org.freedesktop.ColorManager.AlreadyExists:profile ... 
> already exists

Maybe as simple as "Resume Printer" (wouldn't that be wonderful?).

> Best regars,
>   Klaus.


-- 
“The cradle rocks above an abyss, and common sense tells us that our existence
is but a brief crack of light between two eternities of darkness.” 
"Speak, Memory," Vladimir Nabokov

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Klaus Singvogel]

Gene Heskett wrote:
> 
> This is my logs:
> root@coyote:cups$ cat /var/log/cups/access_log
> localhost - - [12/Nov/2019:00:11:00 -0500] "POST / HTTP/1.1" 200 349 
> Create-Printer-Subscriptions successful-ok
> localhost - - [12/Nov/2019:00:11:00 -0500] "POST / HTTP/1.1" 200 176 
> Create-Printer-Subscriptions successful-ok
> root@coyote:cups$ cat /var/log/cups/error_log.1
> E [11/Nov/2019:00:10:25 -0500] Unable to open listen socket for address 
> [v1.::1]:631 - Cannot assign requested address.
> E [11/Nov/2019:16:16:00 -0500] [cups-deviced] PID 22513 (gutenprint52+usb) 
> stopped with status 1!
> E [11/Nov/2019:16:16:00 -0500] [cups-deviced] PID 22511 (begonia) stopped 
> with status 1!
> W [11/Nov/2019:16:18:17 -0500] CreateProfile failed: 
> org.freedesktop.ColorManager.AlreadyExists:profile id 
> \'Brother_HL-2140_series-Gray..\' already exists
> E [11/Nov/2019:16:18:45 -0500] [cups-deviced] PID 22693 (begonia) stopped 
> with status 1!
> E [11/Nov/2019:16:18:45 -0500] [cups-deviced] PID 22695 (gutenprint52+usb) 
> stopped with status 1!
> W [11/Nov/2019:16:20:12 -0500] CreateProfile failed: 
> org.freedesktop.ColorManager.AlreadyExists:profile id 
> \'Brother_HL-2140_series-Gray..\' already exists
> 
> That [v1.::1] looks like shorthand for ipv6, but the nearest ipv6 capable 
> connection is probably 185 miles north of here in Pittsburgh PA.
> There is not AFAIK, any ipv6 provisioned anyplace on my local ISP the 
> local cable folks

Forget this. This message is hours away from your real issue.

Most proably caused by a "Listen [v1.::1]:631" entry in /etc/cups/cupsd.conf

> So thats probably the first thing to fix, but where is it?

No, forget this. Put your focus on that error message:

CreateProfile failed: org.freedesktop.ColorManager.AlreadyExists:profile ... 
already exists

Best regars,
Klaus.
-- 
Klaus Singvogel
GnuPG-Key-ID: 1024R/5068792D  1994-06-27

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Gene Heskett]

Since I installed stretch on this machine, my printer server since the 
early 2000's, suddenly nothing works. No printers are shared despite 
my checking the box to share it during a reconfiguration of that profile.

What do I do to restore what was an "everything just worked" when this 
machine was running wheezy?  All I get in the logs here when another 
machine attempts to print to one of 4 printer profiles seems to 
indicate no permission.

I only have 1 printer defined because I want to fix whatever is wrong 
before I re-add the others. I have ripped out and, killed the etc/cups
directory in hopes a fresh cops install might fix it.  Didn't happen.

This is my logs:
root@coyote:cups$ cat /var/log/cups/access_log
localhost - - [12/Nov/2019:00:11:00 -0500] "POST / HTTP/1.1" 200 349 
Create-Printer-Subscriptions successful-ok
localhost - - [12/Nov/2019:00:11:00 -0500] "POST / HTTP/1.1" 200 176 
Create-Printer-Subscriptions successful-ok
root@coyote:cups$ cat /var/log/cups/error_log.1
E [11/Nov/2019:00:10:25 -0500] Unable to open listen socket for address 
[v1.::1]:631 - Cannot assign requested address.
E [11/Nov/2019:16:16:00 -0500] [cups-deviced] PID 22513 (gutenprint52+usb) 
stopped with status 1!
E [11/Nov/2019:16:16:00 -0500] [cups-deviced] PID 22511 (begonia) stopped with 
status 1!
W [11/Nov/2019:16:18:17 -0500] CreateProfile failed: 
org.freedesktop.ColorManager.AlreadyExists:profile id 
\'Brother_HL-2140_series-Gray..\' already exists
E [11/Nov/2019:16:18:45 -0500] [cups-deviced] PID 22693 (begonia) stopped with 
status 1!
E [11/Nov/2019:16:18:45 -0500] [cups-deviced] PID 22695 (gutenprint52+usb) 
stopped with status 1!
W [11/Nov/2019:16:20:12 -0500] CreateProfile failed: 
org.freedesktop.ColorManager.AlreadyExists:profile id 
\'Brother_HL-2140_series-Gray..\' already exists

That [v1.::1] looks like shorthand for ipv6, but the nearest ipv6 capable 
connection is probably 185 miles north of here in Pittsburgh PA.
There is not AFAIK, any ipv6 provisioned anyplace on my local ISP the 
local cable folks

So thats probably the first thing to fix, but where is it?

An ip a shows
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group 
default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
   valid_lft forever preferred_lft forever
2: eth0:  mtu 1500 qdisc pfifo_fast state UP 
group default qlen 1000
link/ether 00:1f:c6:62:fc:bb brd ff:ff:ff:ff:ff:ff
inet 192.168.71.3/24 brd 192.168.71.255 scope global eth0
   valid_lft forever preferred_lft forever
3: eth1:  mtu 1500 qdisc noop state DOWN group default 
qlen 1000
link/ether 00:1f:c6:63:07:97 brd ff:ff:ff:ff:ff:ff

Nothing is connected at eth1, this mobo has 2 rj45's on it.

And all of that looks like ipv6 crap, yet I have an ipv6 disable in the 
/proc system someplace I've forgotten as this install is now several 
months old. Or is that volatile and needs to be done at every reboot?.

Thanks for any help.

Cheers, Gene Heskett

-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Klaus Singvogel]

Dan Purgert wrote:
> Kent West wrote:
> >
> > Unable to open PPD file:
> >
> > Missing asterisk in column 1
[...]

It's your PPD file for the printer, which seams not to be readable,
most likely not existend.

The PPD (PostScript Printer Defintion) file is locate under /etc/cups/ppds
(or similiar pathname) and named as your "printer name" with suffix ".ppd"

Example: printer name is "oki6EX", than it is /etc/cups/ppds/oki6EX.ppd

Check, if file is existend and readable for cups.

Best regards,
Klaus.
-- 
Klaus Singvogel
GnuPG-Key-ID: 1024R/5068792D  1994-06-27

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

Kent West wrote:
> After some testing, I find that selecting "http" creates a working 
> printer; selecting "ipps" does not. The latter generates an error page 
> that says:
>
> Unable to open PPD file:
>
> Missing asterisk in column 1
>
>
> So apparently there is some difference between these protocols, and I'm 
> left wondering what the differences are, and which one I should select.
>

Most likely, the spooler chokes because you don't have a valid SSL
certificate on the printer (or the print-server). Therefore, neither
"IPPS" nor "HTTPS" would work.

Again, the "choice" of protocol comes down to "what does your printer
support" (most everything newish should support IPP). 

Without getting into way too much detail (and needing to google to
refresh my memory), IPP is basically an "enhanced" LPR/LPD, that instead
of you needing to write all the control software "client side" (i.e. the
machine sending the print job having the options in an rc file, on top
of one or more page filters), an extra communications / settings channel
is opened between the printer and machine trying to print, so they can
communicate about capabilities, and change them on the fly (e.g. want
this job to one-off print single-sided? Just tell the printer), rather
than having to edit a config file (and possibly restart services on the
machine printing).

I believe the newest printers offer a way to print "driverless" via IPP
as well -- that is, rather than needing a device-specific PPD, the use
of IPP lets you just send a standardized "printing format" (PDF, PCL,
something like that), and that "printing format" plus the options you
told it via the control channel gets you a nice document.  Though, that
might just be vaporware at the moment.

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|_|_|O| Github: https://github.com/dpurgert
|O|O|O| PGP: 05CA 9A50 3F2E 1335 4DC5  4AEE 8E11 DDF3 1279 A281

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Kent West]

On 11/11/19 1:44 PM, Kent West wrote:



On 11/11/19 1:38 PM, Kent West wrote:


On 11/11/19 10:40 AM, Brian wrote:

On Mon 11 Nov 2019 at 10:18:26 -0600, Kent West wrote:


When adding a printer via the CUPS web interface (localhost:631) on my
Debian box, Administration / Add Printer / Other Network Printers, 
there are

four Internet Printing Protocol options:

https

ipp

http

ipps

Which one do I want to select? What are the differences?

'ls -l /usr/lib/cups/backend' tells you that it doesn't matter what
choice you make.



lrwxrwxrwx 1 root root  3 Oct 31 02:44 http -> ipp
lrwxrwxrwx 1 root root  3 Oct 31 02:44 https -> ipp
-rwxr-xr-x 1 root root  80120 Oct 31 02:44 ipp
lrwxrwxrwx 1 root root  3 Oct 31 02:44 ipps -> ipp

Thank you. That does tell me they are all the same. It does not tell 
me why CUPS on Debian makes the other three options available 
(thereby confusing the person adding the printer). There must be some 
reason why a person would expect to choose X over Y; that's the 
difference I'm looking for.




After some testing, I find that selecting "http" creates a working 
printer; selecting "ipps" does not. The latter generates an error page 
that says:


Unable to open PPD file:

   Missing asterisk in column 1


So apparently there is some difference between these protocols, and I'm 
left wondering what the differences are, and which one I should select.


--

Kent

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Dan Purgert]

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Kent West wrote:
> Probably answered somewhere, but I've been DuckDuckGo-ing for the past 
> two hours and can't find the answer.
>
> When adding a printer via the CUPS web interface (localhost:631) on my 
> Debian box, Administration / Add Printer / Other Network Printers, there 
> are four Internet Printing Protocol options:
>
> https
>
> ipp
>
> http
>
> ipps
>
> Which one do I want to select? What are the differences?

Whichever your printer supports (consult your manual).  Most would
probably go with ipp (or ipps, if you wanted TLS) these days.

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Re: Difference between ipp, ipps, http, https CUPS protocols?

[Klaus Singvogel]

Kent West wrote:
> 
> lrwxrwxrwx 1 root root  3 Oct 31 02:44 http -> ipp
> lrwxrwxrwx 1 root root  3 Oct 31 02:44 https -> ipp
> -rwxr-xr-x 1 root root  80120 Oct 31 02:44 ipp
> lrwxrwxrwx 1 root root  3 Oct 31 02:44 ipps -> ipp
> 
> Thank you. That does tell me they are all the same. It does not tell me why
> CUPS on Debian makes the other three options available (thereby confusing
> the person adding the printer). There must be some reason why a person would
> expect to choose X over Y; that's the difference I'm looking for.

Not exactly.

Depending on argv[0] (under which name program is started) the program
might work different.

Common practice, if protocols are similiar and only slightly different.

Best regards,
Klaus.
-- 
Klaus Singvogel
GnuPG-Key-ID: 1024R/5068792D  1994-06-27

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Richard Hector]

On 12/11/19 8:38 AM, Kent West wrote:
> 
> On 11/11/19 10:40 AM, Brian wrote:
>> On Mon 11 Nov 2019 at 10:18:26 -0600, Kent West wrote:
>>
>>> Probably answered somewhere, but I've been DuckDuckGo-ing for the
>>> past two
>>> hours and can't find the answer.
>>>
>>> When adding a printer via the CUPS web interface (localhost:631) on my
>>> Debian box, Administration / Add Printer / Other Network Printers,
>>> there are
>>> four Internet Printing Protocol options:
>>>
>>> https
>>>
>>> ipp
>>>
>>> http
>>>
>>> ipps
>>>
>>> Which one do I want to select? What are the differences?
>> 'ls -l /usr/lib/cups/backend' tells you that it doesn't matter what
>> choice you make.
>>
> 
> lrwxrwxrwx 1 root root  3 Oct 31 02:44 http -> ipp
> lrwxrwxrwx 1 root root  3 Oct 31 02:44 https -> ipp
> -rwxr-xr-x 1 root root  80120 Oct 31 02:44 ipp
> lrwxrwxrwx 1 root root  3 Oct 31 02:44 ipps -> ipp
> 
> Thank you. That does tell me they are all the same.

It doesn't tell me that.

It tells me that they're all the same file, but an executable can find
out what name it was called with, and change its behaviour accordingly.
Busybox is an extreme example.

> It does not tell me
> why CUPS on Debian makes the other three options available (thereby
> confusing the person adding the printer). There must be some reason why
> a person would expect to choose X over Y; that's the difference I'm
> looking for.
> 
> But your answer certainly helps. I now know it doesn't matter which of
> these I select.

I would guess that the *s versions use TLS, but beyond that I don't
know. I'd agree with deloptes that it probably depends on what the
remote end can support.

Richard




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Re: Difference between ipp, ipps, http, https CUPS protocols?

[Kent West]

On 11/11/19 1:38 PM, Kent West wrote:


On 11/11/19 10:40 AM, Brian wrote:

On Mon 11 Nov 2019 at 10:18:26 -0600, Kent West wrote:


When adding a printer via the CUPS web interface (localhost:631) on my
Debian box, Administration / Add Printer / Other Network Printers, 
there are

four Internet Printing Protocol options:

https

ipp

http

ipps

Which one do I want to select? What are the differences?

'ls -l /usr/lib/cups/backend' tells you that it doesn't matter what
choice you make.



lrwxrwxrwx 1 root root  3 Oct 31 02:44 http -> ipp
lrwxrwxrwx 1 root root  3 Oct 31 02:44 https -> ipp
-rwxr-xr-x 1 root root  80120 Oct 31 02:44 ipp
lrwxrwxrwx 1 root root  3 Oct 31 02:44 ipps -> ipp

Thank you. That does tell me they are all the same. It does not tell 
me why CUPS on Debian makes the other three options available (thereby 
confusing the person adding the printer). There must be some reason 
why a person would expect to choose X over Y; that's the difference 
I'm looking for.



Okay, just learned why the CUPS web interface presents all four options; 
it's because it's just reading what's available in 
/usr/lib/cups/backend. When I did this:



cd /usr/lib/cups/backend

sudo ln -s ipp bub


I got this when I refreshed my CUPS web interface page:

Other Network Printers: Backend Error Handler
Internet Printing Protocol (https)
Internet Printing Protocol (ipp)
Internet Printing Protocol (http)
AppSocket/HP JetDirect
LPD/LPR Host or Printer
Internet Printing Protocol (ipps)
Internet Printing Protocol (bub)
Windows Printer via SAMBA

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Kent West]

On 11/11/19 10:40 AM, Brian wrote:

On Mon 11 Nov 2019 at 10:18:26 -0600, Kent West wrote:


Probably answered somewhere, but I've been DuckDuckGo-ing for the past two
hours and can't find the answer.

When adding a printer via the CUPS web interface (localhost:631) on my
Debian box, Administration / Add Printer / Other Network Printers, there are
four Internet Printing Protocol options:

https

ipp

http

ipps

Which one do I want to select? What are the differences?

'ls -l /usr/lib/cups/backend' tells you that it doesn't matter what
choice you make.



lrwxrwxrwx 1 root root  3 Oct 31 02:44 http -> ipp
lrwxrwxrwx 1 root root  3 Oct 31 02:44 https -> ipp
-rwxr-xr-x 1 root root  80120 Oct 31 02:44 ipp
lrwxrwxrwx 1 root root  3 Oct 31 02:44 ipps -> ipp

Thank you. That does tell me they are all the same. It does not tell me 
why CUPS on Debian makes the other three options available (thereby 
confusing the person adding the printer). There must be some reason why 
a person would expect to choose X over Y; that's the difference I'm 
looking for.


But your answer certainly helps. I now know it doesn't matter which of 
these I select.


--

Kent

Re: Difference between ipp, ipps, http, https CUPS protocols?

[deloptes]

Brian wrote:

>> When adding a printer via the CUPS web interface (localhost:631) on my
>> Debian box, Administration / Add Printer / Other Network Printers, there
>> are four Internet Printing Protocol options:
>> 
>> https
>> 
>> ipp
>> 
>> http
>> 
>> ipps
>> 
>> Which one do I want to select? What are the differences?
> 
> 'ls -l /usr/lib/cups/backend' tells you that it doesn't matter what
> choice you make.

Hmm, I was thinking it depends on what protocol the printer can talk.

But if it is a network printer it might be supporting all of these.

Re: Difference between ipp, ipps, http, https CUPS protocols?

[Brian]

On Mon 11 Nov 2019 at 10:18:26 -0600, Kent West wrote:

> Probably answered somewhere, but I've been DuckDuckGo-ing for the past two
> hours and can't find the answer.
> 
> When adding a printer via the CUPS web interface (localhost:631) on my
> Debian box, Administration / Add Printer / Other Network Printers, there are
> four Internet Printing Protocol options:
> 
> https
> 
> ipp
> 
> http
> 
> ipps
> 
> Which one do I want to select? What are the differences?

'ls -l /usr/lib/cups/backend' tells you that it doesn't matter what
choice you make.

-- 
Brian.

Difference between ipp, ipps, http, https CUPS protocols?

[Kent West]

Probably answered somewhere, but I've been DuckDuckGo-ing for the past 
two hours and can't find the answer.


When adding a printer via the CUPS web interface (localhost:631) on my 
Debian box, Administration / Add Printer / Other Network Printers, there 
are four Internet Printing Protocol options:


https

ipp

http

ipps

Which one do I want to select? What are the differences?

Thanks!

--

Kent