Network Working Group R. Herriot
Request for Comments: 3510 I. McDonald
Updates: 2910 High North Inc.
Category: Standards Track April 2003

Internet Printing Protocol/1.1:
IPP URL Scheme

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

This memo defines the "ipp" URL (Uniform Resource Locator) scheme.
This memo updates IPP/1.1: Encoding and Transport (RFC2910), by
eXPanding and clarifying Section 5, "IPP URL Scheme", of RFC2910.
An "ipp" URL is used to specify the network location of a print
service that supports the IPP Protocol (RFC2910), or of a network
resource (for example, a print job) managed by sUCh a print service.

Table of Contents

1. Introduction ............................................... 2
2. Terminology ................................................ 3
2.1. Conformance Terminology .............................. 3
2.2. Model Terminology .................................... 3
3. IPP Model for Printers and Jobs ............................ 3
4. IPP URL Scheme ............................................. 4
4.1. IPP URL Scheme Applicability ......................... 4
4.2. IPP URL Scheme Associated Port ....................... 4
4.3. IPP URL Scheme Associated MIME Type .................. 5
4.4. IPP URL Scheme Character Encoding .................... 5
4.5. IPP URL Scheme Syntax ................................ 5
4.6. IPP URL Examples ..................................... 6
4.6.1. IPP Printer URL Examples ..................... 6
4.6.2. IPP Job URL Examples ......................... 6
4.7. IPP URL Comparisons .................................. 7

5. Conformance Requirements ................................... 8
5.1. IPP Client Conformance Requirements .................. 8
5.2. IPP Printer Conformance Requirements ................. 8
6. IANA Considerations ........................................ 9
7. Internationalization Considerations ........................ 9
8. Security Considerations .................................... 9
9. Intellectual Property Rights ............................... 10
10. Normative References ....................................... 11
11. Informative References ..................................... 11
12. Acknowledgments ............................................ 12
Appendix A - Registration of "ipp" URL Scheme .................. 13
Authors' Addresses ............................................. 15
Full Copyright Statement ....................................... 16

1. Introduction

This memo conforms to all of the requirements in Registration
Procedures for URL Scheme Names [RFC2717]. This memo also follows
all of the recommendations in Guidelines for new URL Schemes
[RFC2718].

See section 1, "Introduction", of [RFC2911] and section 1,
"Introduction", of [RFC3196] for overview information about IPP. See
section 10, "Description of the Base IPP Documents", of [RFC3196] for
a full description of the IPP document set.

This memo updates IPP/1.1: Encoding and Transport (RFC2910), by
expanding and clarifying Section 5, "IPP URL Scheme", of RFC2910,
but does not define any new parameters or other new extensions to the
syntax of IPP URLs.

The IPP URL scheme defined in this document is based on the ABNF for
the HTTP URL scheme defined in HTTP [RFC2616], which in turn is
derived from the URI Generic Syntax [RFC2396] and further updated for
IPv6 by [RFC2732]. An IPP URL is transformed into an HTTP URL
according to the rules specified in section 5 of IPP Protocol
[RFC2910].

This document defines IPP URL scheme applicability, associated port
(631), associated MIME type ("application/ipp"), character encoding,
and syntax.

This document is laid out as follows:

- Section 2 defines the terminology used throughout the document.

- Section 3 supplies references to the IPP Printer and IPP Job
object model defined in IPP Model [RFC2911].

- Section 4 specifies the IPP URL scheme.

- Section 5 specifies the conformance requirements for IPP Clients
and IPP Printers that claim conformance to this document.

- Sections 6, 7, and 8 specify IANA, internationalization, and
security considerations.

- Sections 9, 10, 11, 12, and 13 specify normative references,
informative references, acknowledgements, authors' addresses, and
full IETF copyright statement.

- Section 14 (Appendix A) is a completed registration template for
the IPP URL Scheme (see section 6.0 of [RFC2717]).

2. Terminology

This specification document uses the terminology defined in this
section.

2.1. Conformance Terminology

The uppercase terms "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT" "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. These terms are used to specify conformance
requirements for all implementations (both print clients and print
services) of this specification.

2.2. Model Terminology

See section 12.2, "Model Terminology", in IPP Model [RFC2911].

3. IPP Model for Printers and Jobs

See section 2, "IPP Objects", section 2.1, "Printer Object", and
section 2.2, "Job Object", in [RFC2911] for a full description of
the IPP object model and terminology.

In this document, "IPP Client" means the software (on some
hardware platform) that submits, monitors, and/or manages print
jobs via the IPP Protocol [RFC2910] to a print spooler, print
gateway, or physical printing device.

In this document, "IPP Printer object" means the software (on some
hardware platform) that receives print jobs and/or printer/job
operations via the IPP Protocol [RFC2910] from an "IPP Client".

In this document, "IPP Printer" is a synonym for "IPP Printer
object".

In this document, "IPP Job object" means the set of attributes and
documents for one print job instantiated on an "IPP Printer".

In this document, "IPP Job" is a synonym for "IPP Job object".

In this document, "IPP URL" means a URL with the "ipp" scheme.

Note: In this document, "IPP URL" is a synonym for "ipp-URL" (in
section 4, "IPP URL Scheme", of this document) and "ipp-URL" (in
section 5, "IPP URL Scheme", of [RFC2910]).

4. IPP URL Scheme

4.1. IPP URL Scheme Applicability

The "ipp" URL scheme MUST only be used to specify absolute URLs
(relative IPP URLs are not allowed) for IPP print services and
their associated network resources. The "ipp" URL scheme MUST
only be used to specify the use of the abstract protocol defined
in IPP Model [RFC2911] over an HTTP [RFC2616] transport, as
defined in IPP Protocol [RFC2910]. Any other transport binding
for the abstract protocol defined in IPP Model [RFC2911] would
require a different URL scheme.

The "ipp" URL scheme allows an IPP client to choose an appropriate
IPP print service (for example, from a Directory). The IPP client
can establish an HTTP connection to the specified IPP print
service. The IPP client can send IPP protocol requests (for
example, a "Print-Job" request) and receive IPP protocol responses
over that HTTP connection.

4.2. IPP URL Scheme Associated Port

All IPP URLs which do NOT explicitly specify a port MUST be
resolved to IANA-assigned well-known port 631, as registered in
[IANA-PORTREG].

See: IANA Port Numbers Registry [IANA-PORTREG].
See: IPP Protocol [RFC2910].

4.3. IPP URL Scheme Associated MIME Type

All IPP URLs MUST be used to specify network print services which
support the "application/ipp" MIME media type as registered in
[IANA-MIMEREG] for IPP protocol requests and responses.

See: IANA MIME Media Types Registry [IANA-MIMEREG].
See: IPP Protocol [RFC2910].

4.4. IPP URL Scheme Character Encoding

IPP URLs MUST use [RFC2396] encoding, as do their equivalent HTTP
URLs. Characters other than those in the "reserved" and "unsafe"
sets [RFC2396] are equivalent to their ""%" HEX HEX" encoding.

4.5. IPP URL Scheme Syntax

The abstract protocol defined in IPP Model [RFC2911] places a
limit of 1023 octets (NOT characters) on the length of a URI (see
section 4.1.5, "uri", in [RFC2911]).

Note: IPP Printers ought to be cautious about depending on URI
lengths above 255 bytes, because some older client implementations
might not properly support these lengths.

IPP URLs MUST be represented in absolute form. Absolute URLs MUST
always begin with a scheme name followed by a colon. For definitive
information on URL syntax and semantics, see "Uniform Resource
Identifiers (URI): Generic Syntax and Semantics" [RFC2396]. This
specification adopts the definitions of "host", "port", "abs_path",
and "query" from [RFC2396], as updated for IPv6 by [RFC2732].

The IPP URL scheme syntax in ABNF is as follows:

ipp-URL = "ipp:" "//" host [ ":" port ] [ abs_path [ "?" query ]]

If the port is empty or not given, port 631 is assumed. The
semantics are that the identified resource (see section 5.1.2 of
[RFC2616]) is located at the IPP print service listening for HTTP
connections on that port of that host, and the Request-URI for the
identified resource is 'abs_path'.

If the 'abs_path' is not present in the URL, it MUST be given as "/"
when used as a Request-URI for a resource (see section 5.1.2 of
[RFC2616]).

4.6. IPP URL Examples

Note: Literal IPv4 or IPv6 addresses SHOULD NOT be used in IPP URLs.

4.6.1. IPP Printer URL Examples

The following are examples of well-formed IPP URLs for IPP Printers
(for example, to be used as protocol elements in 'printer-uri'
operation attributes of 'Print-Job' request messages):

ipp://example.com
ipp://example.com/printer
ipp://example.com/printer/tiger
ipp://example.com/printer/fox
ipp://example.com/printer/tiger/bob
ipp://example.com/printer/tiger/ira

Each of the above URLs are well-formed URLs for IPP Printers and each
would reference a logically different IPP Printer, even though some
of those IPP Printers might share the same host system. The 'bob' or
'ira' last path components might represent two different physical
printer devices, while 'tiger' might represent some grouping of IPP
Printers (for example, a load-balancing spooler). Or the 'bob' and
'ira' last path components might represent separate human recipients
on the same physical printer device (for example, a physical printer
supporting two job queues). In either case, both 'bob' and 'ira'
would behave as different and independent IPP Printers.

The following are examples of well-formed IPP URLs for IPP Printers
with (optional) ports and paths:

ipp://example.com
ipp://example.com/~smith/printer
ipp://example.com:631/~smith/printer

The first and second IPP URLs above MUST be resolved to port 631
(IANA assigned well-known port for IPP). The second and third IPP
URLs above are equivalent (see section 4.7 below).

4.6.2. IPP Job URL Examples

The following are examples of well-formed IPP URLs for IPP Jobs (for
example, to be used as protocol elements in 'job-uri' attributes of
'Print-Job' response messages):

ipp://example.com/printer/123
ipp://example.com/printer/tiger/job123

IPP Job URLs are valid and meaningful only until Job completion and
possibly an implementation defined optional period of persistence
after Job completion (see IPP Model [RFC2911]).

Ambiguously, section 4.3.1 'job-uri' of IPP Model [RFC2911] states
that:

"the precise format of a Job URI is implementation dependent."

Thus, the relationship between the value of the "printer-uri"
operation attribute used in a 'Print-Job' request and the value of
the "job-uri" attribute returned in the corresponding 'Print-Job'
response is implementation dependent. Also, section 4.3.3 'job-
printer-uri' of IPP Model [RFC2911] states that the 'job-printer-uri'
attribute of a Job object:

"permits a client to identify the Printer object that created this
Job object when only the Job object's URI is available to the
client."

However, the above statement is false, because the transform from an
IPP Job URL to the corresponding IPP Printer URL is unspecified in
either IPP Model [RFC2911] or IPP Protocol [RFC2910].

IPP Printers that conform to this specification SHOULD only generate
IPP Job URLs (for example, in the "job-uri" attribute in a 'Print-
Job' response) by appending exactly one path component to the
corresponding IPP Printer URL (for interoperability).

4.7. IPP URL Comparisons

When comparing two IPP URLs to decide if they match or not, an IPP
Client MUST use the same rules as those defined for HTTP URI
comparisons in [RFC2616], with the sole following exception:

- A port that is empty or not given MUST be treated as equivalent to
the well-known port for that IPP URL (port 631);

See: Section 3.2.3, "URI Comparison", in [RFC2616].

5. Conformance Requirements

5.1. IPP Client Conformance Requirements

IPP Clients that conform to this specification:

a) MUST only send IPP protocol connections to the port specified in
each given IPP URL (if present) or otherwise to IANA assigned
well-known port 631;

b) MUST only send IPP URLs used as protocol elements in outgoing IPP
protocol request messages (for example, in the "printer-uri"
operation attribute in a 'Print-Job' request) that conform to the
ABNF specified in section 4.5, "IPP URL Scheme Syntax, of this
document;

c) MUST only convert IPP URLs to their corresponding HTTP URL forms
according to the rules in section 5, "IPP URL Scheme", in
[RFC2910].

5.2. IPP Printer Conformance Requirements

IPP Printers that conform to this specification:

a) MUST listen for incoming IPP protocol connections on IANA-assigned
well-known port 631, unless explicitly configured by system
administrators or site policies;

b) SHOULD NOT listen for incoming IPP protocol connections on any
other port, unless explicitly configured by system administrators
or site policies;

c) SHOULD only accept IPP URLs used as protocol elements in incoming
IPP protocol request messages (for example, in the "printer-uri"
operation attribute in a 'Print-Job' request) that conform to the
ABNF specified in section 4.5, "IPP URL Scheme Syntax", of this
document;

d) SHOULD only send IPP URLs used as protocol elements in outgoing
IPP protocol response messages (for example, in the "job-uri"
attribute in a 'Print-Job' response) that conform to the ABNF
specified in section 4.5, "IPP URL Scheme Syntax", of this
document;

e) SHOULD only generate IPP Job URLs (for example, in the "job-uri"
attribute in a 'Print-Job' response) by appending exactly one path
component to the corresponding IPP Printer URL (for
interoperability);

f) SHOULD NOT use literal IPv6 or IPv4 addresses in configured or
locally generated IPP URLs.

6. IANA Considerations

This IPP URL Scheme specification does not introduce any additional
IANA considerations, beyond those described in [RFC2910] and
[RFC2911].

See: Section 6, "IANA Considerations" in [RFC2910]
See: Section 6, "IANA Considerations" in [RFC2911].

7. Internationalization Considerations

This IPP URL Scheme specification does not introduce any additional
internationalization considerations, beyond those described in
[RFC2910] and [RFC2911].

See: Section 7, "Internationalization Considerations", in [RFC2910].
See: Section 7, "Internationalization Considerations", in [RFC2911].

8. Security Considerations

This IPP URL Scheme specification does not introduce any additional
security considerations, beyond those described in [RFC2910] and
[RFC2911], except the following:

a) An IPP URL might be faked to point to a rogue IPP print service,
thus collecting confidential document contents from IPP clients.
Server authentication mechanisms and security mechanisms specified
in the IPP Protocol [RFC2910] are sufficient to address this
threat.

b) An IPP URL might be used to Access an IPP print service by an
unauthorized IPP client. Client authentication mechanisms and
security mechanisms specified in the IPP Protocol [RFC2910] are
sufficient to address this threat.

c) An IPP URL might be used to access an IPP print service at a print
protocol application layer gateway (for example, an IPP to LPD
gateway [RFC2569]) causing silent compromise of IPP security
mechanisms. There is no practical defense against this threat by
a client system. System administrators should avoid such
compromising configurations.

d) An IPP URL does not have parameters to specify the required client
authentication mechanism (for example, 'certificate' as defined in
section 4.4.2, "uri-authentication-supported", of IPP Model

[RFC2911]) and required security mechanism (for example, 'tls' as
defined in section 4.4.3, "uri-security-supported", of IPP Model
[RFC2911]). Service discovery or directory protocols might be
used to discover the required client authentication and security
mechanisms associated with given IPP URLs.

Historical Note: During the development of this document,
consideration was given to the addition of standard IPP URL
parameters for the client authentication and security mechanisms.
However, based on a strong IETF IPP Working Group consensus, no
parameters were added to the "ipp" URL scheme as originally defined
in IPP Protocol [RFC2910] in September 2000, for reasons of backwards
compatibility with the many currently shipping implementations of
IPP/1.1.

See: Section 8, "Security Considerations", in [RFC2910].
See: Section 8, "Security Considerations", in [RFC2911].

9. Intellectual Property Rights

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
oBTain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.

10. Normative References

[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC2234, November 1997.

[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter,
"Uniform Resource Identifiers (URI): Generic Syntax",
RFC2396, August 1998.

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC2616, June 1999.

[RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format for
Literal IPv6 Addresses in URL's", RFC2732, December
1999.

[RFC2910] Herriot, R., Butler, S., Moore, P., Turner, R. and J.
Wenn, "IPP/1.1 Encoding and Transport [IPP Protocol]",
RFC2910, September 2000.

[RFC2911] Hastings, T., Herriot, R., deBry, R., Isaacson, S. and
P. Powell, "IPP/1.1 Model and Semantics [IPP Model]",
RFC2911, September 2000.

[US-ASCII] Coded Character Set -- 7-bit American Standard Code
for Information Interchange, ANSI X3.4-1986.

11. Informative References

[IANA-MIMEREG] IANA MIME Media Types Registry.
FTP://ftp.iana.org/in-notes/iana/assignments/media-
types/...

[IANA-PORTREG] IANA Port Numbers Registry. ftp://ftp.iana.org/in-
notes/iana/assignments/port-numbers

[RFC2569] Herriot, R., Hastings, T., Jacobs, N. and J. Martin,
"Mapping between LPD and IPP Protocols", RFC2569,
April 1999.

[RFC2717] Petke, R. and I. King, "Registration Procedures for
URL Scheme Names", RFC2717, November 1999.

[RFC2718] Masinter, L., Alvestrand, H., Zigmond, D. and R.
Petke, "Guidelines for new URL Schemes", RFC2718,
November 1999.

[RFC3196] Hastings, T., Manros, C., Zehler, P., Kugler, C. and
H. Holst, "Internet Printing Protocol/1.1:
Implementor's Guide", RFC3196, November 2001.

12. Acknowledgments

This document is a product of the Internet Printing Protocol Working
Group of the Internet Engineering Task Force (IETF).

Thanks to Pat Fleming (IBM), Tom Hastings (Xerox), Harry Lewis (IBM),
Hugo Parra (Novell), Don Wright (Lexmark), and all the members of the
IETF IPP WG.

Section 5, "IPP URL Scheme", in IPP Protocol [RFC2910] was the
primary input to this IPP URL Scheme specification.

Appendix A - Registration of "ipp" URL Scheme

Note: The following registration obsoletes section 5, "IPP URL
Scheme", of IPP Protocol [RFC2911].

URL Scheme Name: ipp

URL Scheme Syntax:

ipp-URL = "ipp:" "//" host [ ":" port ] [ abs_path [ "?" query ]]

Character Encoding Considerations:

IPP URLs MUST use [RFC2396] encoding, as do their equivalent HTTP
URLs. Characters other than those in the "reserved" and "unsafe"
sets [RFC2396] are equivalent to their ""%" HEX HEX" encoding.

Intended Usage:

The intended usage of the "ipp" URL scheme is COMMON.

An "ipp" URL is used to specify the network location of a print
service that supports the IPP Protocol [RFC2910], or of a network
resource (for example, a print job) managed by such a print
service. An IPP client can choose to establish an HTTP connection
to the specified print service for transmission of IPP protocol
requests (for example, IPP print job submission requests).

Applications or Protocols which use this URL scheme:

See: Section 5, "IPP URL Scheme", in IPP Protocol [RFC2910].

Interoperability Considerations:

See: Section 9, "Interoperability with IPP/1.0 Implementations",
in IPP Protocol [RFC2910].

Security Considerations:

See: Section 8, "Security Considerations", in IPP Protocol
[RFC2910].

Relevant Publications:

[RFC2910] Herriot, R., Butler, S., Moore, P., Turner, R. and J. Wenn,
"IPP/1.1 Encoding and Transport [IPP Protocol]", RFC2910,
September 2000.

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,
L., Leach, P. and T. Berners-Lee, "Hypertext Transfer
Protocol -- HTTP/1.1", RFC2616, June 1999.

[RFC3510] Herriot, R. and I. McDonald, "IPP/1.1: IPP URL Scheme", RFC
3510, April 2003.

Person & email address to contact for further information:

Robert Herriot
Consultant
706 Colorado Ave
Palo Alto, CA 94303

Phone: +1 650-327-4466
EMail: bob@herriot.com

Ira McDonald
High North Inc
221 Ridge Ave
Grand Marais, MI 49839

Phone: +1 906-494-2434
EMail: imcdonald@sharplabs.com

Authors' Addresses

Robert Herriot
Consultant
706 Colorado Ave
Palo Alto, CA 94303

Phone: +1 650-327-4466
EMail: bob@herriot.com

Ira McDonald
High North Inc
221 Ridge Ave
Grand Marais, MI 49839

Phone: +1 906-494-2434
EMail: imcdonald@sharplabs.com

Usage questions and comments on this IPP URL Scheme should be sent
directly to the editors at their above addresses (and to the IPP
mailing list, if you are a subscriber - see below).

IPP Web Page: http://www.pwg.org/ipp/
IPP Mailing List: ipp@pwg.org

To subscribe to the IPP mailing list, send the following email:

1) send it to majordomo@pwg.org

2) leave the subject line blank

3) put the following two lines in the message body: subscribe ipp

Implementers of this specification are encouraged to join the IPP
Mailing List in order to participate in any discussions of
clarification issues and comments. In order to reduce spam the
mailing list rejects mail from non-subscribers, so you must subscribe
to the mailing list in order to send a question or comment to the IPP
mailing list.

Full Copyright Statement

Copyright (C) The Internet Society (2003). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
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The limited permissions granted above are perpetual and will not be
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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