Towards Requirements for IP Routers
RFC 1716

Document Type RFC - Informational (November 1994; No errata)
Obsoleted by RFC 1812
Last updated 2013-03-02
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Network Working Group                                P. Almquist, Author
Request for Comments: 1716                                    Consultant
Category: Informational                            F. Kastenholz, Editor
                                                      FTP Software, Inc.
                                                           November 1994

                  Towards Requirements for IP Routers

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Almquist & Kastenholz                                           [Page i]


RFC 1716          Towards Requirements for IP Routers      November 1994

Table of Contents

0.  PREFACE .......................................................    1
1.  INTRODUCTION ..................................................    2
1.1  Reading this Document ........................................    4
1.1.1  Organization ...............................................    4
1.1.2  Requirements ...............................................    5
1.1.3  Compliance .................................................    6
1.2  Relationships to Other Standards .............................    7
1.3  General Considerations .......................................    8
1.3.1  Continuing Internet Evolution ..............................    8
1.3.2  Robustness Principle .......................................    9
1.3.3  Error Logging ..............................................    9
1.3.4  Configuration ..............................................   10
1.4  Algorithms ...................................................   11
2.  INTERNET ARCHITECTURE .........................................   13
2.1  Introduction .................................................   13
2.2  Elements of the Architecture .................................   14
2.2.1  Protocol Layering ..........................................   14
2.2.2  Networks ...................................................   16
2.2.3  Routers ....................................................   17
2.2.4  Autonomous Systems .........................................   18
2.2.5  Addresses and Subnets ......................................   18
2.2.6  IP Multicasting ............................................   20
2.2.7  Unnumbered Lines and Networks and Subnets ..................   20
2.2.8  Notable Oddities ...........................................   22
2.2.8.1  Embedded Routers .........................................   22
2.2.8.2  Transparent Routers ......................................   23
2.3  Router Characteristics .......................................   24
2.4  Architectural Assumptions ....................................   27
3.  LINK LAYER ....................................................   29
3.1  INTRODUCTION .................................................   29
3.2  LINK/INTERNET LAYER INTERFACE ................................   29
3.3  SPECIFIC ISSUES ..............................................   30
3.3.1  Trailer Encapsulation ......................................   30
3.3.2  Address Resolution Protocol - ARP ..........................   31
3.3.3  Ethernet and 802.3 Coexistence .............................   31
3.3.4  Maximum Transmission Unit - MTU ............................   31
3.3.5  Point-to-Point Protocol - PPP ..............................   32
3.3.5.1  Introduction .............................................   32
3.3.5.2  Link Control Protocol (LCP) Options ......................   33
3.3.5.3  IP Control Protocol (ICP) Options ........................   34
3.3.6  Interface Testing ..........................................   35
4.  INTERNET LAYER - PROTOCOLS ....................................   36
4.1  INTRODUCTION .................................................   36
4.2  INTERNET PROTOCOL - IP .......................................   36

Almquist & Kastenholz                                          [Page ii]


RFC 1716          Towards Requirements for IP Routers      November 1994

4.2.1  INTRODUCTION ...............................................   36
4.2.2  PROTOCOL WALK-THROUGH ......................................   37
4.2.2.1  Options: RFC-791 Section 3.2 .............................   37
4.2.2.2  Addresses in Options: RFC-791 Section 3.1 ................   40
4.2.2.3  Unused IP Header Bits: RFC-791 Section 3.1 ...............   40
4.2.2.4  Type of Service: RFC-791 Section 3.1 .....................   41
4.2.2.5  Header Checksum: RFC-791 Section 3.1 .....................   41
4.2.2.6  Unrecognized Header Options: RFC-791 Section 3.1 .........   41
4.2.2.7  Fragmentation: RFC-791 Section 3.2 .......................   42
4.2.2.8  Reassembly: RFC-791 Section 3.2 ..........................   43
4.2.2.9  Time to Live: RFC-791 Section 3.2 ........................   43
4.2.2.10  Multi-subnet Broadcasts: RFC-922 ........................   43
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