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Internet Protocol
RFC 791

Document type: RFC - Internet Standard (September 1981; Errata)
Obsoletes RFC 760
Document stream: Legacy
Last updated: 2013-03-02
Other versions: plain text, pdf, html

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

IESG State: RFC 791 (Internet Standard)
Responsible AD: (None)
Send notices to: No addresses provided

RFC:  791
                                    
                                    
                                    
                                    
                                    
                                    
                                    
                           INTERNET PROTOCOL
                                    
                                    
                         DARPA INTERNET PROGRAM
                                    
                         PROTOCOL SPECIFICATION
                                    
                                    
                                    
                             September 1981

                              prepared for

               Defense Advanced Research Projects Agency
                Information Processing Techniques Office
                         1400 Wilson Boulevard
                       Arlington, Virginia  22209

                                   by

                     Information Sciences Institute
                   University of Southern California
                           4676 Admiralty Way
                   Marina del Rey, California  90291





September 1981                                                          
                                                       Internet Protocol

                           TABLE OF CONTENTS

    PREFACE ........................................................ iii

1.  INTRODUCTION ..................................................... 1

  1.1  Motivation .................................................... 1
  1.2  Scope ......................................................... 1
  1.3  Interfaces .................................................... 1
  1.4  Operation ..................................................... 2

2.  OVERVIEW ......................................................... 5

  2.1  Relation to Other Protocols ................................... 9
  2.2  Model of Operation ............................................ 5
  2.3  Function Description .......................................... 7
  2.4  Gateways ...................................................... 9

3.  SPECIFICATION ................................................... 11

  3.1  Internet Header Format ....................................... 11
  3.2  Discussion ................................................... 23
  3.3  Interfaces ................................................... 31

APPENDIX A:  Examples & Scenarios ................................... 34
APPENDIX B:  Data Transmission Order ................................ 39

GLOSSARY ............................................................ 41

REFERENCES .......................................................... 45

                                                                [Page i]



                                                          September 1981
Internet Protocol

[Page ii]                                                               



September 1981                                                          
                                                       Internet Protocol

                                PREFACE

This document specifies the DoD Standard Internet Protocol.  This
document is based on six earlier editions of the ARPA Internet Protocol
Specification, and the present text draws heavily from them.  There have
been many contributors to this work both in terms of concepts and in
terms of text.  This edition revises aspects of addressing, error
handling, option codes, and the security, precedence, compartments, and
handling restriction features of the internet protocol.

                                                           Jon Postel

                                                           Editor

                                                              [Page iii]





                                                          September 1981

RFC:  791
Replaces:  RFC 760
IENs 128, 123, 111,
80, 54, 44, 41, 28, 26

                           INTERNET PROTOCOL

                         DARPA INTERNET PROGRAM
                         PROTOCOL SPECIFICATION

                            1.  INTRODUCTION

1.1.  Motivation

  The Internet Protocol is designed for use in interconnected systems of
  packet-switched computer communication networks.  Such a system has
  been called a "catenet" [1].  The internet protocol provides for
  transmitting blocks of data called datagrams from sources to
  destinations, where sources and destinations are hosts identified by
  fixed length addresses.  The internet protocol also provides for
  fragmentation and reassembly of long datagrams, if necessary, for
  transmission through "small packet" networks.

1.2.  Scope

  The internet protocol is specifically limited in scope to provide the

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