Requirements for IP Version 4 Routers
RFC 1812

Document Type RFC - Proposed Standard (June 1995; Errata)
Updated by RFC 2644, RFC 6633
Obsoletes RFC 1716, RFC 1009
Last updated 2013-03-02
Stream IETF
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IESG IESG state RFC 1812 (Proposed Standard)
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Network Working Group                                   F. Baker, Editor
Request for Comments: 1812                                 Cisco Systems
Obsoletes: 1716, 1009                                          June 1995
Category: Standards Track

                 Requirements for IP Version 4 Routers

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.

PREFACE

   This document is an updated version of RFC 1716, the historical
   Router Requirements document.  That RFC preserved the significant
   work that went into the working group, but failed to adequately
   describe current technology for the IESG to consider it a current
   standard.

   The current editor had been asked to bring the document up to date,
   so that it is useful as a procurement specification and a guide to
   implementors.  In this, he stands squarely on the shoulders of those
   who have gone before him, and depends largely on expert contributors
   for text.  Any credit is theirs; the errors are his.

   The content and form of this document are due, in large part, to the
   working group's chair, and document's original editor and author:
   Philip Almquist.  It is also largely due to the efforts of its
   previous editor, Frank Kastenholz.  Without their efforts, this
   document would not exist.

Table of Contents

   1. INTRODUCTION ........................................    6
   1.1 Reading this Document ..............................    8
   1.1.1 Organization .....................................    8
   1.1.2 Requirements .....................................    9
   1.1.3 Compliance .......................................   10
   1.2 Relationships to Other Standards ...................   11
   1.3 General Considerations .............................   12
   1.3.1 Continuing Internet Evolution ....................   12
   1.3.2 Robustness Principle .............................   13
   1.3.3 Error Logging ....................................   14

Baker                       Standards Track                     [Page 1]
RFC 1812         Requirements for IP Version 4 Routers         June 1995

   1.3.4 Configuration ....................................   14
   1.4 Algorithms .........................................   16
   2. INTERNET ARCHITECTURE ...............................   16
   2.1 Introduction .......................................   16
   2.2 Elements of the Architecture .......................   17
   2.2.1 Protocol Layering ................................   17
   2.2.2 Networks .........................................   19
   2.2.3 Routers ..........................................   20
   2.2.4 Autonomous Systems ...............................   21
   2.2.5 Addressing Architecture ..........................   21
   2.2.5.1 Classical IP Addressing Architecture ...........   21
   2.2.5.2 Classless Inter Domain Routing (CIDR) ..........   23
   2.2.6 IP Multicasting ..................................   24
   2.2.7 Unnumbered Lines and Networks Prefixes ...........   25
   2.2.8 Notable Oddities .................................   26
   2.2.8.1 Embedded Routers ...............................   26
   2.2.8.2 Transparent Routers ............................   27
   2.3 Router Characteristics .............................   28
   2.4 Architectural Assumptions ..........................   31
   3. LINK LAYER ..........................................   32
   3.1 INTRODUCTION .......................................   32
   3.2 LINK/INTERNET LAYER INTERFACE ......................   33
   3.3 SPECIFIC ISSUES ....................................   34
   3.3.1 Trailer Encapsulation ............................   34
   3.3.2 Address Resolution Protocol - ARP ................   34
   3.3.3 Ethernet and 802.3 Coexistence ...................   35
   3.3.4 Maximum Transmission Unit - MTU ..................   35
   3.3.5 Point-to-Point Protocol - PPP ....................   35
   3.3.5.1 Introduction ...................................   36
   3.3.5.2 Link Control Protocol (LCP) Options ............   36
   3.3.5.3 IP Control Protocol (IPCP) Options .............   38
   3.3.6 Interface Testing ................................   38
   4. INTERNET LAYER - PROTOCOLS ..........................   39
   4.1 INTRODUCTION .......................................   39
   4.2 INTERNET PROTOCOL - IP .............................   39
   4.2.1 INTRODUCTION .....................................   39
   4.2.2 PROTOCOL WALK-THROUGH ............................   40
   4.2.2.1 Options: RFC 791 Section 3.2 ...................   40
   4.2.2.2 Addresses in Options: RFC 791 Section 3.1 ......   42
   4.2.2.3 Unused IP Header Bits: RFC 791 Section 3.1 .....   43
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