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


   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

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  The update to RFC2474  . . . . . . . . . . . . . . . . . . . .  4
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5  4
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  5
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  5
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  6  5
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  6
     7.2.  Informative References . . . . . . . . . . . . . . . . . .  6
   Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . .  6
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  8  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].

                  | 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,
   i.e., values are assigned by Action
   (Section 4.9 of [RFC8126] defines this as "assigned only through
   Standards Track or Best Current Practice
   RFCs, allowing these codepoints to be assigned. 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.

   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], i.e.,  values are
   assigned only through Standards Track or Best Current Practice RFCs
   in the IETF Stream. [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",
   "OPTIONAL" in this document are to be interpreted as described in

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
   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 a Standards Action assignment
   policy. 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" 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
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, <

   [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-

   [RFC3260]  Grossman, D., "New Terminology and Clarifications for
              Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,

   [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

              IANA, "Differentiated Services Field Codepoints (DSCP),
              registry.xhtml", .

7.2.  Informative References

              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,

Appendix A.  Revision Notes

   Note to RFC-Editor: please remove this entire section prior to

   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.

   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

   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
   Godred Fairhurst
   University of Aberdeen
   Department of Engineering
   Fraser Noble Building
   Aberdeen, AB24 3UE