RFC 940 (rfc940) - Page 1 of 3

Toward an Internet standard scheme for subnetting

Network Working Group                                               GADS
Request for Comments: 940 
                                                              April 1985

           Toward an Internet Standard Scheme for Subnetting


STATUS OF THIS MEMO

   This RFC discusses standardizing the protocol used in subnetted
   environments in the ARPA-Internet.  Distribution of this memo is
   unlimited.

   The author of this RFC is the Gateway Algorithms and Data Structures
   (GADS) Task Force, chaired by David L. Mills.

INTRODUCTION

   Several sites now contain a complex of local links connected to the
   Internet via a gateway.  The details of the internal connectivity are
   of little interest to the rest of the Internet.

   One way of organizing these local complexes of links is to use the
   same strategy as the Internet uses to organize networks, that is, to
   declare each link to be an entity (like a network) and to
   interconnect the links with devices that perform routing functions
   (like gateways).  This general scheme is called subnetting, the
   individual links are called subnets, and the connecting devices are
   called subgateways (or bridges, or gateways).

   All hosts in the Internet must make a decision when sending a
   datagram, that is, they must answer the question "Is this datagram
   addressed to a host on a directly connected network, or must it be
   sent to a gateway?".  In a subnetted environment, this question is
   extended to "Is this datagram addressed to a host on a directly
   connected subnet, or must it be sent to a (sub)gateway?".  Let us
   call answering this question "making the routing decision".

   Because the hosts used in a subnetted environment must implement in
   their IP or network interface software procedures for making the
   routing decision, and because such hosts may be acquired from various
   sources, it is important that a standard subnetting scheme be
   identified so that different suppliers can provide compatible hosts
   (that is, hosts compatible with the complexes at different sites and
   each other).  Without a designated standard for a subnetting scheme
   suppliers can not create compatible hosts.

   The potential problem is that if different subnetting schemes are
   developed by different suppliers a customer that installs hosts from
   two or more suppliers may find that they do not work together.



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