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Type of Service in the Internet Protocol Suite
RFC 1349

Document type: RFC - Proposed Standard (July 1992)
Obsoleted by RFC 2474
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Document shepherd: No shepherd assigned

IESG State: RFC 1349 (Proposed Standard)
Responsible AD: (None)
Send notices to: No addresses provided

Network Working Group                                        P. Almquist
Request for Comments: 1349                                    Consultant
Updates: RFCs 1248, 1247, 1195,                                July 1992
         1123, 1122, 1060, 791

             Type of Service in the Internet Protocol Suite

Status of This Memo

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

Summary

   This memo changes and clarifies some aspects of the semantics of the
   Type of Service octet in the Internet Protocol (IP) header.  The
   handling of IP Type of Service by both hosts and routers is specified
   in some detail.

   This memo defines a new TOS value for requesting that the network
   minimize the monetary cost of transmitting a datagram.  A number of
   additional new TOS values are reserved for future experimentation and
   standardization.  The ability to request that transmission be
   optimized along multiple axes (previously accomplished by setting
   multiple TOS bits simultaneously) is removed.  Thus, for example, a
   single datagram can no longer request that the network simultaneously
   minimize delay and maximize throughput.

   In addition, there is a minor conflict between the Host Requirements
   (RFC-1122 and RFC-1123) and a number of other standards concerning
   the sizes of the fields in the Type of Service octet.  This memo
   resolves that conflict.

Table of Contents

   1.  Introduction ...............................................    3

   2.  Goals and Philosophy .......................................    3

   3.  Specification of the Type of Service Octet .................    4

   4.  Specification of the TOS Field .............................    5

Almquist                                                        [Page 1]



RFC 1349                    Type of Service                    July 1992

   5.  Use of the TOS Field in the Internet Protocols .............    6
      5.1  Internet Control Message Protocol (ICMP) ...............    6
      5.2  Transport Protocols ....................................    7
      5.3  Application Protocols ..................................    7

   6.  ICMP and the TOS Facility ..................................    8
      6.1  Destination Unreachable ................................    8
      6.2  Redirect ...............................................    9

   7.  Use of the TOS Field in Routing ............................    9
      7.1  Host Routing ...........................................   10
      7.2  Forwarding .............................................   12

   8.  Other consequences of TOS ..................................   13

   APPENDIX A.  Updates to Other Specifications ...................   14
      A.1  RFC-792 (ICMP) .........................................   14
      A.2  RFC-1060 (Assigned Numbers) ............................   14
      A.3  RFC-1122 and RFC-1123 (Host Requirements) ..............   16
      A.4  RFC-1195 (Integrated IS-IS) ............................   16
      A.5  RFC-1247 (OSPF) and RFC-1248 (OSPF MIB) ................   17

   APPENDIX B.  Rationale .........................................   18
      B.1  The Minimize Monetary Cost TOS Value ...................   18
      B.2  The Specification of the TOS Field .....................   19
      B.3  The Choice of Weak TOS Routing .........................   21
      B.4  The Retention of Longest Match Routing .................   22
      B.5  The Use of Destination Unreachable .....................   23

   APPENDIX C.  Limitations of the TOS Mechanism ..................   24
      C.1  Inherent Limitations ...................................   24
      C.2  Limitations of this Specification ......................   25

   References .....................................................   27

   Acknowledgements ...............................................   28

   Security Considerations ........................................   28

   Author's Address ...............................................   28

Almquist                                                        [Page 2]



RFC 1349                    Type of Service                    July 1992

1.  Introduction

   Paths through the Internet vary widely in the quality of service they
   provide.  Some paths are more reliable than others.  Some impose high
   call setup or per-packet charges, while others do not do usage-based
   charging.  Throughput and delay also vary widely.  Often there are
   tradeoffs: the path that provides the highest throughput may well not
   be the one that provides the lowest delay or the lowest monetary

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