Re-assignment of Pool 3 of the DSCP Registry to assignment by IETF Standards Action
draft-fairhurst-tsvwg-iana-dscp-registry-00

Abstract

The Differentiated Services (Diffserv) architecture specifies use of the DSField in the IPv4 and IPv6 packet header to carry the Diffserv Codepoint (DSCP). The Internet Assigned Numbers Authority (IANA) maintains a registry of assigned DSCP values.

This update to RFC2474 requests a change to the IANA assignment method for Pool 3 of the registry to change this to Standards Action assignment. The update also removes permission for Local Use of the codepoints that form Pool 3 of the DSCP registry.

Status of This Memo

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This Internet-Draft will expire on June 17, 2018.

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Table of Contents

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

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 DSField, 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 DSField 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 [RFC2474], which were initially "available for experimental or local use, but which were indicated should be preferentially utilized for standardized assignments if Pool 1 is ever exhausted."

+------+-----------------+
| Pool | Codepoint Space |
+------+-----------------+
|  1   |     xxxxx0      |
+------+-----------------+
|  2   |     xxxx11      |
+------+-----------------+
|  3   |     xxxx01      |
+------+-----------------+

Figure 1: Format of the DSField for Codepoints allocated in the
three IANA pools (where 'x' refers to either '0' or '1').

At the time of writing this document, 23 of the 32 Pool 1 codepoints have currently been assigned. Although Pool 1 has not yet been completely exhausted, this document requests IANA to change the use of Pool 3 to allow assignment to this pool. The rationale for this request is a need to assign codepoints for particular PHBs that are unable to use any of the unassigned values in Pool 1.

An example is the need to assign a suitable 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 may preempt it. This use case requires a DSCP with a zero value for the first three bits [I-D.ietf-tsvwg-le-phb]. At the same time, it is also important to reduce the probability of accidental re-mapping of other (higher assurance) traffic to the DSCP used for the LE PHB. Since there are no unassigned codepoints in Pool 1 that exhibit the required properties, this motivates the desire to allow the IETF to use a codepoint in Pool 3.

To allow the IETF to utilise Pool 3 codepoints, this document requests IANA to manage Pool 3 and make assignments for DSCP codepoints in Pool 3 when requested by Standards Action. This assignment method requires publication of a Standards Track RFC approved by the IESG.

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 method:

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 format is shown in Figure 2.

              Pool        Codepoint space          Assignment Policy
              ----        ---------------          -----------------
              
              1            xxxxx0                 Standards Action
              2            xxxx11                 EXP/LU
              3            xxxx01                 Standards Action
              
              Figure 2: Updated Assignment Policy for the DSCP Registry

4. Security Considerations

Security considerations for the use of DSCPs 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 method.

This requests IANA to make the following changes to the Differentiated Services Field Codepoints (DSCP) Registry, made available at [Registry].

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" entry. Pool 3 of the registry is to be created initially empty, with a format identical to that used for "Pool 1 Codepoints".

The Registration Procedure for use of Pool 3 is "Standards Action" [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 need to be explained in the IANA considerations requesting this assignment.

IANA is requested to reference RFC3260 and this current document.

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

7.2. Informative References

Appendix A. Revision Notes

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

This document is an individual submission, seeking adoption by the Transport and Services Working Group (TSVWG).

Inidividual submission as draft -00.

• This is the initial version of the document.
• Advice in this rev. from Michelle Cotton on the IANA procedure.
• Thanks to Brian Carpenter for helpful inputs to this ID.

Author's Address