RFC 1812: Requirements for IP Version 4 Routers | RFC Editor

Skip to content Primary navigationThe RFC SeriesFor AuthorsAbout UsHomeRFC 1812 View as: Plain Text, Compact HTML Info RFC 1812: Requirements for IP Version 4 RoutersIPv4routingJune 1995. F. Baker, Ed.Proposed StandardSubscribe6 subscribed Add to Set Read aloud This RFC was updated, see RFC 2644, RFC 6633.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 4.2.2.4 Type of Service: RFC 791 Section 3.1 ........... 44 4.2.2.5 Header Checksum: RFC 791 Section 3.1 ........... 44 4.2.2.6 Unrecognized Header Options: RFC 791, Section 3.1 .................................... 44 4.2.2.7 Fragmentation: RFC 791 Section 3.2 ............. 45 4.2.2.8 Reassembly: RFC 791 Section 3.2 ................ 46 4.2.2.9 Time to Live: RFC 791 Section 3.2 .............. 46 4.2.2.10 Multi-subnet Broadcasts: RFC 922 .............. 47 Baker Standards Track [Page 2] RFC 1812 Requirements for IP Version 4 Routers June 1995 4.2.2.11 Addressing: RFC 791 Section 3.2 ............... 47 4.2.3 SPECIFIC ISSUES .................................. 50 4.2.3.1 IP Broadcast Addresses ......................... 50 4.2.3.2 IP Multicasting ................................ 50 4.2.3.3 Path MTU Discovery ............................. 51 4.2.3.4 Subnetting ..................................... 51 4.3 INTERNET CONTROL MESSAGE PROTOCOL - ICMP ........... 52 4.3.1 INTRODUCTION ..................................... 52 4.3.2 GENERAL ISSUES ................................... 53 4.3.2.1 Unknown Message Types .......................... 53 4.3.2.2 ICMP Message TTL .