draft-ietf-tsvwg-iana-dscp-registry-04.txt   draft-ietf-tsvwg-iana-dscp-registry-05.txt 
Transport Area Working Group G. Fairhurst Transport Area Working Group G. Fairhurst
Internet-Draft University of Aberdeen Internet-Draft University of Aberdeen
Updates: 2474 (if approved) May 08, 2018 Updates: 2474 (if approved) May 10, 2018
Intended status: Standards Track Intended status: Standards Track
Expires: November 07, 2018 Expires: November 09, 2018
IANA Assignment of DSCP Pool 3 (xxxx01) Values to require Publication of IANA Assignment of DSCP Pool 3 (xxxx01) Values to require Publication of
a Standards Track or Best Current Practice RFC a Standards Track or Best Current Practice RFC
draft-ietf-tsvwg-iana-dscp-registry-04 draft-ietf-tsvwg-iana-dscp-registry-05
Abstract Abstract
The Differentiated Services (Diffserv) architecture specifies use of The Differentiated Services (Diffserv) architecture specifies use of
a field in the IPv4 and IPv6 packet headers to carry Diffserv a field in the IPv4 and IPv6 packet headers to carry Diffserv
Codepoint (DSCP) values. The Internet Assigned Numbers Authority Codepoint (DSCP) values. The Internet Assigned Numbers Authority
(IANA) maintains a registry of assigned DSCP values. (IANA) maintains a registry of assigned DSCP values.
This update to RFC2474 changes the IANA assignment method for Pool 3 This update to RFC2474 changes the IANA assignment method for Pool 3
of the registry (i.e., DSCP values of the form xxxx01) to Standards of the registry (i.e., DSCP values of the form xxxx01) to Standards
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 07, 2018. This Internet-Draft will expire on November 09, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (http://trustee.ietf.org/ Provisions Relating to IETF Documents (http://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License. provided without warranty as described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The update to RFC2474 . . . . . . . . . . . . . . . . . . . . 4 3. The update to RFC2474 . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . . 6 Appendix A. Revision Notes . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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the Internet. Diffserv uses the six most significant bits of the the Internet. Diffserv uses the six most significant bits of the
former IPv4 Type of Service (TOS) octet or the former IPv6 Traffic 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 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 Codepoint (DSCP). This DSCP value is used to select a Diffserv Per
hop Behaviour, PHB. hop Behaviour, PHB.
The six bit field is capable of conveying 64 distinct codepoints, and The six bit field is capable of conveying 64 distinct codepoints, and
this codepoint space has been divided into three pools for the this codepoint space has been divided into three pools for the
purpose of codepoint assignment and management (as shown in figure purpose of codepoint assignment and management (as shown in figure
1). Pool 1 comprises 32 codepoints [RFC2474]. These are assigned by 1). Pool 1 comprises 32 codepoints [RFC2474]. These are assigned by
Standards Action, as defined in [RFC8126]. Pool 2 comprises a pool Standards Action, as defined in [RFC8126], i.e., values are assigned
of 16 codepoints reserved for experimental or Local Use (EXP/LU) as by Standards Track or Best Current Practice RFCs. Pool 2 comprises a
defined in [RFC2474], and Pool 3 comprises 16 codepoints, which were pool of 16 codepoints reserved for experimental or Local Use (EXP/LU)
specified as "initially available for experimental or local use, but as defined in [RFC2474], and Pool 3 comprises 16 codepoints, which
which should be preferentially utilized for standardized assignments were specified as "initially available for experimental or local use,
if Pool 1 is ever exhausted" [RFC2474]. but which should be preferentially utilized for standardized
assignments if Pool 1 is ever exhausted" [RFC2474].
+------+-----------------+ +------+-----------------+
| Pool | Codepoint Space | | Pool | Codepoint Space |
+------+-----------------+ +------+-----------------+
| 1 | xxxxx0 | | 1 | xxxxx0 |
+------+-----------------+ +------+-----------------+
| 2 | xxxx11 | | 2 | xxxx11 |
+------+-----------------+ +------+-----------------+
| 3 | xxxx01 | | 3 | xxxx01 |
+------+-----------------+ +------+-----------------+
Figure 1: Format of the field for codepoints allocated in the Figure 1: Format of the field for codepoints allocated in the
three IANA pools (where 'x' refers to either '0' or '1'). 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 At the time of writing this document, 22 of the 32 Pool 1 codepoints
have currently been assigned. have currently been assigned.
Although Pool 1 has not yet been completely exhausted, this document Although Pool 1 has not yet been completely exhausted, there is a
changes the IANA registration policy of Pool 3 to assignment by need to assign codepoints for particular PHBs that are unable to use
Standards Action, i.e., values are assigned by Standards Track or any of the unassigned values in Pool 1. This document changes the
Best Current Practice RFCs. The rationale for this update is a need IANA registration policy of Pool 3 to assignment by Standards Action,
to assign codepoints for particular PHBs that are unable to use any i.e., values are assigned by Standards Track or Best Current Practice
of the unassigned values in Pool 1. RFCs, allowing these codepoints to be assigned.
An example is the need to assign a suitable recommended default An example is the need to assign a suitable recommended default
codepoint for the Lower Effort (LE) per-hop behavior (PHB) [I-D.ietf- 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) tsvwg-le-phb]. The LE PHB is designed to protect best-effort (BE)
traffic (packets forwarded with the default PHB) from LE traffic in traffic (packets forwarded with the default PHB) from LE traffic in
congestion situations, i.e., when resources become scarce, best- congestion situations (i.e., when resources become scarce, best-
effort traffic has precedence over LE traffic and may preempt it. effort traffic has precedence over LE traffic and is allowed to
The continued presence of bleaching of the IP precedence field, preempt it). The continued presence of bleaching of the IP precedence
setting the first three bits of the former TOS byte to zero (i.e., field in deployed networks can result in setting the first three bits
zeroing the top three bits of the DSCP) in deployed networks of the former TOS byte to zero (disabling any class-based flow
motivates the desire for the LE PHB to use a DSCP with a zero value management by routers configured with TOS-based packet processing).
for the first three bits [I-D.ietf-tsvwg-le-phb]. At the same time, There is a need to avoid this remapping of the DSCP for the LE PHB by
it is also important to reduce the likelihood of priority inversion assigning a codepoint that has a zero value in the first three bits
caused by unintentional re-mapping of other (higher assurance) [I-D.ietf-tsvwg-le-phb]. Furthermore, if the LE PHB were to have
traffic to the DSCP used for this PHB. The absence of unassigned been assigned one of the currently unused Pool 1 codepoints with a
codepoints in Pool 1 that exhibit these important properties zero value in the first three bits, any bleaching of the IP
motivates assigning a Pool 3 codepoint as the default that is precedence field would result in other (higher assurance) traffic
recommended for use with this PHB. 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 To allow the IETF to utilise Pool 3 codepoints, this document
requests IANA to to manage Pool 3 assignments for DSCP values in Pool requests IANA to to manage Pool 3 assignments for DSCP values in Pool
3 via the Standards Action policy [RFC8126]. This assignment method 3 via the Standards Action policy [RFC8126]. This assignment method
requires publication of a Standards Track or Best Current Practice requires publication of a Standards Track or Best Current Practice
RFC. RFC.
2. Terminology 2. Terminology
This document assumes familiarity with the terminology used in This document assumes familiarity with the terminology used in
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Working Group submission as draft -03 Working Group submission as draft -03
o Corrections after TSVWG Shepherd Review. o Corrections after TSVWG Shepherd Review.
Working Group submission as draft -04 Working Group submission as draft -04
o Added RFC 3260 as a necessary downref, with IANA asked to o Added RFC 3260 as a necessary downref, with IANA asked to
reference this. 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.
Author's Address Author's Address
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Department of Engineering Department of Engineering
Fraser Noble Building Fraser Noble Building
Aberdeen, AB24 3UE Aberdeen, AB24 3UE
Scotland Scotland
Email: gorry@erg.abdn.ac.uk Email: gorry@erg.abdn.ac.uk
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