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+Internet Engineering Task Force (IETF)                      G. Fairhurst
+Request for Comments: 8436                        University of Aberdeen
+Updates: 2474                                                August 2018
+Category: Standards Track
+ISSN: 2070-1721
+
+
+    Update to IANA Registration Procedures for Pool 3 Values in the
+        Differentiated Services Field Codepoints (DSCP) Registry
+
+Abstract
+
+   The Differentiated Services (Diffserv) architecture specifies use of
+   the DS field in the IPv4 and IPv6 packet headers to carry one of 64
+   distinct differentiated services field codepoint (DSCP) values.  The
+   Internet Assigned Numbers Authority (IANA) maintains a registry of
+   assigned DSCP values.
+
+   This update to RFC 2474 changes the IANA registration 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 is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 7841.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   https://www.rfc-editor.org/info/rfc8436.
+
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+Fairhurst                    Standards Track                    [Page 1]
+
+RFC 8436      IANA Registration Procedures for DSCP Pool 3   August 2018
+
+
+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
+   Provisions Relating to IETF Documents
+   (https://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+Table of Contents
+
+   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
+   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
+   3.  The Updates to RFC 2474 . . . . . . . . . . . . . . . . . . .   4
+   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
+   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
+   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
+     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
+     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
+   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   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 DSCP.
+   This DSCP value is used to select a Diffserv per-hop behavior (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].  Pool 3 comprises 16
+   codepoints, which were originally specified as "initially available
+   for experimental or local use, but which should be preferentially
+   utilized for standardized assignments if Pool 1 is ever exhausted" by
+   [RFC2474].
+
+
+
+Fairhurst                    Standards Track                    [Page 2]
+
+RFC 8436      IANA Registration Procedures for DSCP Pool 3   August 2018
+
+
+                  +------+-----------------+
+                  | 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 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) PHB [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 (when
+   resources become scarce, best-effort traffic has precedence over LE
+   traffic and is allowed to preempt it).  In deployed networks,
+   bleaching (i.e. intentionally setting to zero) of the IP Precedence
+   field continues to be used.  (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.  Therefore, there is 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 [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.  Therefore, it is 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.
+
+
+
+Fairhurst                    Standards Track                    [Page 3]
+
+RFC 8436      IANA Registration Procedures for DSCP Pool 3   August 2018
+
+
+   To allow the IETF to utilize Pool 3 codepoints, this document
+   requests IANA 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
+   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
+   capitals, as shown here.
+
+3.  The Updates to RFC 2474
+
+   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 RFC 2474 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
+
+
+
+
+
+
+
+Fairhurst                    Standards Track                    [Page 4]
+
+RFC 8436      IANA Registration Procedures for DSCP Pool 3   August 2018
+
+
+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
+
+   IANA has changed the use of Pool 3 in the "Differentiated Services
+   Field Codepoints (DSCP)" registry and will manage this pool using
+   Standards Action, as defined as Section 4.9 of [RFC8126].
+
+   IANA has made the following changes to the "Differentiated Services
+   Field Codepoints (DSCP)" registry, made available at [Registry].
+
+   IANA has referenced RFC 2474 and Section 4 of RFC 3260 for the
+   overall format of this registry.
+
+   IANA has referenced RFC 2474 and Section 4 of RFC 3260 for Pool 1.
+
+   This document 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 for Pool 3:
+
+      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 has created and will maintain
+   the "DSCP Pool 3 Codepoints" subregistry.  Pool 3 of the registry has
+   been created initially empty, with a format identical to that used
+   for "DSCP Pool 1 Codepoints".
+
+   IANA has referenced RFC 2474, Section 4 of RFC 3260, 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 it
+   MAY make assignments from Pool 3 when 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 section of the document that requests any
+   assignment from Pool 3.
+
+
+
+Fairhurst                    Standards Track                    [Page 5]
+
+RFC 8436      IANA Registration Procedures for DSCP Pool 3   August 2018
+
+
+6.  References
+
+6.1.  Normative References
+
+   [Registry]
+              IANA, "Differentiated Services Field Codepoints (DSCP)",
+              <https://www.iana.org/assignments/dscp-registry/>.
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119,
+              DOI 10.17487/RFC2119, March 1997,
+              <https://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,
+              <https://www.rfc-editor.org/info/rfc2474>.
+
+   [RFC3260]  Grossman, D., "New Terminology and Clarifications for
+              Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
+              <https://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>.
+
+   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
+              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
+              May 2017, <https://www.rfc-editor.org/info/rfc8174>.
+
+6.2.  Informative References
+
+   [LE-PHB]   Bless, R., "A Lower Effort Per-Hop Behavior (LE PHB)",
+              Work in Progress, draft-ietf-tsvwg-le-phb-05, July 2018.
+
+   [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,
+              <https://www.rfc-editor.org/info/rfc2475>.
+
+Acknowledgments
+
+   Godred Fairhurst received funding from the European Union's Horizon
+   2020 research and innovation program 2014-2018 under grant agreement
+   No. 644334 (NEAT).
+
+
+
+
+Fairhurst                    Standards Track                    [Page 6]
+
+RFC 8436      IANA Registration Procedures for DSCP Pool 3   August 2018
+
+
+Author's Address
+
+   Godred Fairhurst
+   University of Aberdeen
+   Department of Engineering
+   Fraser Noble Building
+   Aberdeen  AB24 3UE
+   United Kingdom
+
+   Email: gorry@erg.abdn.ac.uk
+   URI:   http://www.erg.abdn.ac.uk/
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+Fairhurst                    Standards Track                    [Page 7]
+