IETF S. Brim
Internet Draft B. Carpenter
April 1999
Per Hop Behavior Identification Codes
Copyright Notice
Placeholder for ISOC copyright.
Abstract
draft-brim-diffserv-phbid-00.txt
This document defines a 16 bit encoding mechanism for the identification
of differentiated services Per Hop Behaviors in protocol messages.
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Table of Contents:
Status of this Memo.............................................1
1. Introduction.................................................3
2. Encoding.....................................................3
3. IANA Considerations..........................................4
4. Security considerations......................................5
Acknowledgements................................................5
References......................................................5
Authors' Addresses..............................................5
Intellectual Property...........................................6
Full Copyright Statement........................................6
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1. Introduction
Differentiated Services [RFC 2474, RFC 2475] introduces the notion of
Per Hop Behaviors (PHBs) that define how traffic belonging to a
particular behavior aggregate is treated at an individual network
node. In IP packet headers, PHBs are not indicated as such; instead
Differentiated Services Codepoint (DSCP) values are used. There are
only 64 possible DSCP values, but there is no such limit on the
number of PHBs. In a given network domain, there is a locally defined
mapping between DSCP values and PHBs. Standardized PHBs recommend a
DSCP mapping, but network operators may choose alternative mappings.
In some cases it is necessary or desirable to identify a particular
PHB in a protocol message, such as a message negotiating bandwidth
management or path selection. Examples where work is in progress
include communication between bandwidth brokers, and MPLS support of
diffserv.
In certain cases, what needs to be identified is not an individual
PHB, but a set of PHBs. One example is a set of PHBs that must follow
the same physical path to prevent re-ordering. An instance of this
is the set of three PHBs belonging to a single Assured Forwarding
class, such as the PHBs AF11, AF12 and AF13 [Assured].
This document defines a binary encoding to uniquely identify PHBs
and/or sets of PHBs in protocol messages. This encoding MUST be used
when such identification is required.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Encoding
PHBs and sets of PHBs are encoded in an unsigned 16 bit binary field,
using the same encoding. It is determined by context whether the
encoding represents a PHB or a set of PHBs.
The 16 bit field is arranged as follows:
Case 1: PHBs defined by standards action, as per [RFC 2474].
The encoding for a single PHB is the recommended DSCP value for that
PHB, left-justified in the 16 bit field, with bits 6 through 15 set
to zero. Note that the recommended DSCP value MUST be used, even if
the network in question has chosen a different mapping.
The encoding for a set of PHBs is the numerically smallest of the set
of encodings for the various PHBs in the set. (Thus for the AF1x
PHBs, the encoding is that of the AF11 PHB.)
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| DSCP | 0 0 0 0 0 0 0 0 0 0 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Case 2: PHBs not defined by standards action, i.e. experimental or
local use PHBs as allowed by [RFC 2474]. In this case an arbitrary 12
bit PHB identification code, assigned by the IANA, is placed left-
justified in the 16 bit field, and bits 12 through 15 contain the
value 0x1.
A set of non-standard PHBs is identified by a single PHB
identification code.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| PHB id code | 0 0 0 1 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Bits 12 through 14 are reserved either for expansion of the PHB
identification code, or for other use such as distinguishing PHB
groups from individual PHBs, at some point in the future.
3. IANA Considerations
IANA is requested to create a new assignment registry for "Per-Hop
Behavior Identification Codes", initially allowing values in the
range 0 to 4095 decimal.
Assignment of values in this field require:
-the identity of the assignee
-a brief description of the new PHB, with enough detail to
distinguish it from existing standardized and non-standardized
PHBs. In the case of a set of PHBs, this description should cover
all PHBs in the set.
-a reference to a stable document describing the PHB in detail.
During the first year of existence of this registry, IANA is
requested to refer all requests to the IETF diffserv WG for review.
Subsequently, requests should be reviewed by the IETF Transport Area
Directors or by an expert that they designate.
If the number of assignments begins to approach 4096, the Transport
Area Directors should be alerted.
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4. Security considerations
This encoding in itself raises no security issues. However, users of
this encoding should consider that modifying a PHB identification
code may constitute theft or denial of service, so protocols using
this encoding must be adequately protected.
Acknowledgements
Useful comments were made by Francois Le Faucheur and others.
References
[RFC 2119] Key words for use in RFCs to Indicate Requirement Levels,
S. Bradner, RFC 2119, March 1997.
[RFC 2474] Definition of the Differentiated Services Field (DS Field)
in the IPv4 and IPv6 Headers. K. Nichols, S. Blake, F. Baker, D.
Black, RFC 2474, December 1998.
[RFC 2475] An Architecture for Differentiated Services. S. Blake, D.
Black, M. Carlson, E. Davies, Z. Wang, W. Weiss, RFC 2475, December
1998.
[Assured] Assured Forwarding PHB Group, J. Heinanen, F. Baker, W.
Weiss, J. Wroclawski, draft-ietf-diffserv-af-06.txt, work in
progress.
Authors' Addresses
Scott W. Brim
146 Honness Lane
Ithaca, NY 14850
USA
E-mail: swb@newbridge.com
Brian E. Carpenter
IBM United Kingdom Laboratories
MP 185, Hursley Park
Winchester, Hampshire SO21 2JN, UK
E-mail: brian@hursley.ibm.com
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Intellectual Property
PLACEHOLDER for full IETF IPR Statement if needed.
Full Copyright Statement
PLACEHOLDER for full ISOC copyright Statement if needed.
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