RAP: Internet Route Access Protocol
RFC 1476

Document Type RFC - Experimental (June 1993; No errata)
Last updated 2013-03-02
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Network Working Group                                        R. Ullmann
Request for Comments: 1476                 Process Software Corporation
                                                              June 1993

                  RAP: Internet Route Access Protocol

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard.  Discussion and
   suggestions for improvement are requested.  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.

Abstract

   This RFC describes an open distance vector routing protocol for use
   at all levels of the internet, from isolated LANs to the major
   routers of an international commercial network provider.

Table of Contents

   1.       Introduction  . . . . . . . . . . . . . . . . . . . 2
   1.1       Link-State and Distance-Vector . . . . . . . . . . 3
   1.2       Terminology  . . . . . . . . . . . . . . . . . . . 3
   1.3       Philosophy . . . . . . . . . . . . . . . . . . . . 3
   2.       RAP Protocol  . . . . . . . . . . . . . . . . . . . 4
   2.1       Command Header Format  . . . . . . . . . . . . . . 4
   2.1.1     Length field . . . . . . . . . . . . . . . . . . . 4
   2.1.2     RAP version  . . . . . . . . . . . . . . . . . . . 5
   2.2       RAP Commands . . . . . . . . . . . . . . . . . . . 5
   2.2.1     No operation . . . . . . . . . . . . . . . . . . . 5
   2.2.2     Poll . . . . . . . . . . . . . . . . . . . . . . . 6
   2.2.3     Error  . . . . . . . . . . . . . . . . . . . . . . 7
   2.2.4     Add Route  . . . . . . . . . . . . . . . . . . . . 8
   2.2.5     Purge Route  . . . . . . . . . . . . . . . . . . . 9
   3.       Attributes of Routes  . . . . . . . . . . . . . . . 9
   3.1       Metric and Option Format . . . . . . . . . . . . .10
   3.1.1     Option Class . . . . . . . . . . . . . . . . . .  10
   3.1.2     Type . . . . . . . . . . . . . . . . . . . . . .  10
   3.1.3     Format . . . . . . . . . . . . . . . . . . . . .  11
   3.2       Metrics and Options  . . . . . . . . . . . . . .  11
   3.2.1     Distance . . . . . . . . . . . . . . . . . . . .  12
   3.2.2     Delay  . . . . . . . . . . . . . . . . . . . . .  12
   3.2.3     MTU  . . . . . . . . . . . . . . . . . . . . . .  12
   3.2.4     Bandwidth  . . . . . . . . . . . . . . . . . . .  12

Ullmann                                                         [Page 1]
RFC 1476                          RAP                          June 1993

   3.2.5     Origin . . . . . . . . . . . . . . . . . . . . .  12
   3.2.6     Target . . . . . . . . . . . . . . . . . . . . .  13
   3.2.7     Packet Cost  . . . . . . . . . . . . . . . . . .  13
   3.2.8     Time Cost  . . . . . . . . . . . . . . . . . . .  13
   3.2.9     Source Restriction . . . . . . . . . . . . . . .  14
   3.2.10    Destination Restriction  . . . . . . . . . . . .  14
   3.2.11    Trace  . . . . . . . . . . . . . . . . . . . . .  14
   3.2.12    AUP  . . . . . . . . . . . . . . . . . . . . . .  15
   3.2.13    Public . . . . . . . . . . . . . . . . . . . . .  15
   4.       Procedure   . . . . . . . . . . . . . . . . . . .  15
   4.1       Receiver filtering . . . . . . . . . . . . . . .  16
   4.2       Update of metrics and options  . . . . . . . . .  16
   4.3       Aggregation  . . . . . . . . . . . . . . . . . .  17
   4.4       Active route selection . . . . . . . . . . . . .  17
   4.5       Transmitter filtering  . . . . . . . . . . . . .  17
   4.6       Last resort loop prevention  . . . . . . . . . .  18
   5.       Conclusion  . . . . . . . . . . . . . . . . . . .  18
   6.       Appendix: Real Number Representation  . . . . . .  19
   7.       References  . . . . . . . . . . . . . . . . . . .  20
   8.       Security Considerations . . . . . . . . . . . . .  20
   9.       Author's Address  . . . . . . . . . . . . . . . .  20

1.  Introduction

   RAP is a general protocol for distributing routing information at all
   levels of the Internet, from private LANs to the widest-flung
   international carrier networks.  It does not distinguish between
   "interior" and "exterior" routing (except as restricted by specific
   policy), and therefore is not as restricted nor complex as those
   protocols that have strict level and area definitions in their
   models.

   The protocol encourages the widest possible dissemination of topology
   information, aggregating it only when limits of thrust, bandwidth, or
   administrative policy require it.  Thus RAP permits aggressive use of
   resources to optimize routes where desired, without the restrictions
   inherent in the simplifications of other models.

   While RAP uses IPv7 [RFC1475] addressing internally, it is run over
   both IPv4 and IPv7 networks, and shares routing information between
   them.  A IPv4 router will only be able to activate and propagate
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