RFC 917 (rfc917) - Page 1 of 22

Internet subnets

Network Working Group                                      Jeffrey Mogul
Request for Comments: 917                    Computer Science Department
                                                     Stanford University
                                                            October 1984

                            INTERNET SUBNETS


Status Of This Memo

   This RFC suggests a proposed protocol for the ARPA-Internet
   community, and requests discussion and suggestions for improvements.
   Distribution of this memo is unlimited.

Overview

   We discuss the utility of "subnets" of Internet networks, which are
   logically visible sub-sections of a single Internet network.  For
   administrative or technical reasons, many organizations have chosen
   to divide one Internet network into several subnets, instead of
   acquiring a set of Internet network numbers.

   We propose procedures for the use of subnets, and discuss approaches
   to solving the problems that arise, particularly that of routing.

Acknowledgment

   This proposal is the result of discussion with several other people.
   J. Noel Chiappa, Chris Kent, and Tim Mann, in particular, provided
   important suggestions.

1. Introduction

   The original view of the Internet universe was a two-level hierarchy:
   the top level the catenet as a whole, and the level below it a
   collection of "Internet Networks", each with its own Network Number.
   (We do not mean that the Internet has a hierarchical topology, but
   that the interpretation of addresses is hierarchical.)

   While this view has proved simple and powerful, a number of
   organizations have found it inadequate and have added a third level
   to the interpretation of Internet addresses.  In this view, a given
   Internet Network might (or might not) be divided into a collection of
   subnets.

   The original, two-level, view carries a strong presumption that, to a
   host on an Internet network, that network may be viewed as a single
   edge; to put it another way, the network may be treated as a "black
   box" to which a set of hosts is connected.  This is true of the




Mogul