RFC 2873 (rfc2873) - Page 1 of 8

TCP Processing of the IPv4 Precedence Field

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Network Working Group                                            X. Xiao
Request for Comments: 2873                               Global Crossing
Category: Standards Track                                      A. Hannan
                                                                    iVMG
                                                               V. Paxson
                                                              ACIRI/ICSI
                                                               E. Crabbe
                                                   Exodus Communications
                                                               June 2000


              TCP Processing of the IPv4 Precedence Field

Status of this Memo

   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 (2000).  All Rights Reserved.

Abstract

   This memo describes a conflict between TCP [RFC 793] and DiffServ
   [RFC 2475] on the use of the three leftmost bits in the TOS octet of
   an IPv4 header [RFC 791]. In a network that contains DiffServ-capable
   nodes, such a conflict can cause failures in establishing TCP
   connections or can cause some established TCP connections to be reset
   undesirably. This memo proposes a modification to TCP for resolving
   the conflict.

   Because the IPv6 [RFC 2460] traffic class octet does not have any
   defined meaning except what is defined in RFC 2474, and in particular
   does not define precedence or security parameter bits, there is no
   conflict between TCP and DiffServ on the use of any bits in the IPv6
   traffic class octet.

1. Introduction

   In TCP, each connection has a set of states associated with it. Such
   states are reflected by a set of variables stored in the TCP Control
   Block (TCB) of both ends. Such variables may include the local and
   remote socket number, precedence of the connection, security level




Xiao, et al.                Standards Track
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