Internet DRAFT - draft-ietf-tsvwg-iana-dscp-registry
draft-ietf-tsvwg-iana-dscp-registry
Transport Area Working Group G. Fairhurst
Internet-Draft University of Aberdeen
Updates: 2474 (if approved) June 07, 2018
Intended status: Standards Track
Expires: December 07, 2018
IANA Assignment of DSCP Pool 3 (xxxx01) Values to require Publication of
a Standards Track or Best Current Practice RFC
draft-ietf-tsvwg-iana-dscp-registry-08
Abstract
The Differentiated Services (Diffserv) architecture specifies use of
a field in the IPv4 and IPv6 packet headers to carry Diffserv
Codepoint (DSCP) values. The Internet Assigned Numbers Authority
(IANA) maintains a registry of assigned DSCP values.
This update to RFC2474 changes the IANA assignment policy for Pool 3
of the registry (i.e., DSCP values of the form xxxx01) to Standards
Action, i.e., values are assigned through a Standards Track or Best
Current Practice RFC. The update also removes permission for
experimental and Local Use of the Codepoints that form Pool 3 of the
DSCP registry; Pool 2 Codepoints (i.e., DSCP values of the form
xxxx11) remain available for these purposes.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 07, 2018.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The update to RFC2474 . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The Differentiated Services (Diffserv) [RFC2475] architecture
(updated by [RFC3260]) provides scalable service differentiation in
the Internet. Diffserv uses the six most significant bits of the
former IPv4 Type of Service (TOS) octet or the former IPv6 Traffic
Class octet to convey the field, which is used to carry the Diffserv
Codepoint (DSCP). This DSCP value is used to select a Diffserv Per
hop Behaviour, PHB.
The six bit field is capable of conveying 64 distinct codepoints, and
this codepoint space has been divided into three pools for the
purpose of codepoint assignment and management (as shown in figure
1). Pool 1 comprises 32 codepoints [RFC2474]. These are assigned by
Standards Action, as defined in [RFC8126]. Pool 2 comprises a pool
of 16 codepoints reserved for experimental or Local Use (EXP/LU) as
defined in [RFC2474], and Pool 3 comprises 16 codepoints, which were
specified as "initially available for experimental or local use, but
which should be preferentially utilized for standardized assignments
if Pool 1 is ever exhausted" [RFC2474].
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+------+-----------------+
| Pool | Codepoint Space |
+------+-----------------+
| 1 | xxxxx0 |
+------+-----------------+
| 2 | xxxx11 |
+------+-----------------+
| 3 | xxxx01 |
+------+-----------------+
Figure 1: Format of the field for codepoints allocated in the
three IANA pools (where 'x' refers to either '0' or '1').
At the time of writing this document, 22 of the 32 Pool 1 codepoints
have currently been assigned.
Although Pool 1 has not yet been completely exhausted, there is a
need to assign codepoints for particular PHBs that are unable to use
any of the unassigned values in Pool 1. This document changes the
IANA registration policy of Pool 3 to assignment by Standards Action
(Section 4.9 of [RFC8126] defines this as "assigned only through
Standards Track or Best Current Practice RFCs in the IETF Stream").
An example is the need to assign a suitable recommended default
codepoint for the Lower Effort (LE) per-hop behavior (PHB) [I-D.ietf-
tsvwg-le-phb]. The LE PHB is designed to protect best-effort (BE)
traffic (packets forwarded with the default PHB) from LE traffic in
congestion situations (i.e., when resources become scarce, best-
effort traffic has precedence over LE traffic and is allowed to
preempt it). In deployed networks, there is continued use of
bleaching (i.e. intentionally setting to zero) of the IP precedence
field. (Setting the IP Precedence field to zero disables any class-
based flow management by routers configured with TOS-based packet
processing). This causes the first three bits of the former TOS byte
(now the upper part of the DSCP field) to become zero. There is
therefore a need to avoid this remapping of the DSCP for the LE PHB
by assigning a codepoint that already has a zero value in the first
three bits [I-D.ietf-tsvwg-le-phb].
Furthermore, if the LE PHB were to have been assigned one of the
currently unused Pool 1 codepoints with a zero value in the first
three bits, any bleaching of the IP precedence field would result in
other (higher assurance) traffic being also remapped to the assigned
DSCP. This remapping could then cause diffserv-marked traffic to
receive an unintentional LE treatment for the remainder of the
Internet path. It is therefore important to avoid the resulting
priority inversion. The absence of unassigned codepoints in Pool 1
that exhibit these important properties motivates assigning a Pool 3
codepoint as the default that is recommended for use with this PHB.
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To allow the IETF to utilise Pool 3 codepoints, this document
requests IANA to to manage Pool 3 assignments for DSCP values in Pool
3 via the Standards Action policy [RFC8126].
2. Terminology
This document assumes familiarity with the terminology used in
[RFC2475] updated by [RFC3260].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
3. The update to RFC2474
This document updates section 6 of [RFC2474], in the following ways.
It updates the following text concerning the assignment policy:
OLD: which are initially available for experimental or local use, but
which should be preferentially utilized for standardized
assignments if Pool 1 is ever exhausted.
NEW: which are utilized for standardized assignments (replacing the
previous availability for experimental or local use).
It removes the footnote in RFC2474 relating to Pool 3:
DELETE: "(*) may be utilized for future Standards Action allocations
as necessary"
The new registry assignment policy is shown in Figure 2.
Pool Codepoint space Assignment Policy
---- --------------- ------------------
1 xxxxx0 Standards Action
2 xxxx11 EXP/LU
3 xxxx01 Standards Action
Note for Pool 2: "Reserved for experimental or Local Use"
Figure 2: Updated Assignment Policy for the DSCP Registry
4. Security Considerations
Security considerations for the use of DSCP values are described in
the RFCs that define their usage. This document does not present new
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security considerations.
5. IANA Considerations
This section requests IANA to change the use of Pool 3 in the DSCP
registry and to manage this pool using Standards Action, as defined
as Section 4.9 of [RFC8126].
This requests IANA to make the following changes to the
Differentiated Services field Codepoints (DSCP) Registry, made
available at [Registry].
IANA is requested to reference RFC2474 and Section 4 of RFC3260 for
the overall format of the DSCP registry.
IANA is requested to reference RFC2474 and Section 4 of RFC3260 for
Pool 1.
This update does not modify the IANA registry text for Pool 2. This
pool continues to preserve the note shown in Figure 2.
The previous registry text:
3 xxxx01 Experimental or Local Use May be utilized for future
Standards Action allocations as necessary.
is replaced with the following registry text:
3 xxxx01 Standards Action.
To manage codepoints in Pool 3, IANA is requested to create and
maintain a "Pool 3 Codepoints" subregistry. Pool 3 of the registry
is to be created initially empty, with a format identical to that
used for "Pool 1 Codepoints".
IANA is requested to reference RFC2474, Section 4 of RFC3260, and the
current document for Pool 3.
The Registration Procedure for use of Pool 3 is Standards Action, as
defined as Section 4.9 of [RFC8126]. IANA is expected to normally
make assignments from Pool 1, until this Pool is exhausted, but MAY
make assignments from Pool 3 where the format of the codepoint has
properties that are needed for a specific PHB. The required
characteristics for choosing a requested DSCP value MUST be explained
in the IANA considerations of the document that requests any
assignment from Pool 3.
6. Acknowledgments
G. Fairhurst received funding from the European Union's Horizon 2020
research and innovation program 2014-2018 under grant agreement No.
644334 (NEAT).
7. References
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7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, <http://www.rfc-editor.org/info/
rfc2119>.
[RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI
10.17487/RFC2474, December 1998, <http://www.rfc-
editor.org/info/rfc2474>.
[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
<http://www.rfc-editor.org/info/rfc3260>.
[RFC8126] Cotton, M., Leiba, B. and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www
.rfc-editor.org/info/rfc8126>.
[Registry]
IANA, "Differentiated Services Field Codepoints (DSCP),
https://www.iana.org/assignments/dscp-registry/dscp-
registry.xhtml", .
7.2. Informative References
[I-D.ietf-tsvwg-le-phb]
Bless, R., "A Lower Effort Per-Hop Behavior (LE PHB)",
Internet-Draft draft-ietf-tsvwg-le-phb-02, June 2017.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<http://www.rfc-editor.org/info/rfc2475>.
Appendix A. Revision Notes
Note to RFC-Editor: please remove this entire section prior to
publication.
Individual submission as draft -00.
o This is the initial version of the document.
o Advice in this rev. from Michelle Cotton on the IANA procedure.
o Thanks to Brian Carpenter for helpful inputs to this ID.
Individual submission as draft -01.
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o Thanks to Roland Bless for review comments.
Individual submission as draft -02 (author requests adoption as a
TSVWG WG draft).
o Thanks to David Black for review comments in preparing rev -02.
Working Group submission as draft -00
o Adopted by the TSVWG working group.
Working Group submission as draft -01
o Fixed exploded acronyms.
Working Group submission as draft -02
o Corrections after WGLC.
Working Group submission as draft -03
o Corrections after TSVWG Shepherd Review.
Working Group submission as draft -04
o Added RFC 3260 as a necessary downref, with IANA asked to
reference this.
Working Group submission as draft -05
o Corrections following AD review.
o Expansion of explanation about why the proposed change will help
in assignment of a suitable DSCP for the LE PHB.
Working Group submission as draft -06
o GenART feedback to changed assignment method to assignment
policy,.
o Correction to the IANA reference documents.
Working Group submission as draft -07
o Revised after IESG feedback - Assignment Policy changed final para
text; Figure 2 reference changed; bleaching defined; definition of
standards action aligned with actual IANA policy.
Working Group submission as draft -08
o Revised after AD feedback - definition of standards action.
Author's Address
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Godred Fairhurst
University of Aberdeen
Department of Engineering
Fraser Noble Building
Aberdeen, AB24 3UE
Scotland
Email: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/
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