RFC - 2474

Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers

Original:	ftp://ftp.isi.edu/in-notes/rfc2474.txt
Authors:	K. Nichols [Cisco Systems], S. Blake [Torrent Networking Technologies], F. Baker [Cisco Systems], D. Black [EMC Corporation]
Date:	December 1998
Category:	Proposed Standard

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Obsoletes:
RFC-1455	Physical Link Security Type of Service (Obsoleted by RFC-2474prop)
RFC-1349	Type of Service in the Internet Protocol Suite (Obsoleted by RFC-2474prop)

Updated by:
RFC-3260	New Terminology and Clarifications for Diffserv
RFC-3168prop	The Addition of Explicit Congestion Notification (ECN) to IP

Referred by:	87 RFC
Refers to:	9 RFC

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Status

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1998). All Rights Reserved.

Abstract

Differentiated services enhancements to the Internet protocol are intended to enable scalable service discrimination in the Internet without the need for per-flow state and signaling at every hop. A variety of services may be built from a small, well-defined set of building blocks which are deployed in network nodes. The services may be either end-to-end or intra-domain; they include both those that can satisfy quantitative performance requirements (e.g., peak bandwidth) and those based on relative performance (e.g., "class" differentiation). Services can be constructed by a combination of:

• setting bits in an IP header field at network boundaries (autonomous system boundaries, internal administrative boundaries, or hosts),
• using those bits to determine how packets are forwarded by the nodes inside the network, and
• conditioning the marked packets at network boundaries in accordance with the requirements or rules of each service.

The requirements or rules of each service must be set through administrative policy mechanisms which are outside the scope of this document. A differentiated services-compliant network node includes a classifier that selects packets based on the value of the DS field, along with buffer management and packet scheduling mechanisms capable of delivering the specific packet forwarding treatment indicated by the DS field value. Setting of the DS field and conditioning of the temporal behavior of marked packets need only be performed at network boundaries and may vary in complexity.

This document defines the IP header field, called the DS (for differentiated services) field. In IPv4, it defines the layout of the TOS octet; in IPv6, the Traffic Class octet. In addition, a base set of packet forwarding treatments, or per-hop behaviors, is defined.

For a more complete understanding of differentiated services, see also the differentiated services architecture [ARCH].

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