Browse Prior Art Database

Subnetwork addressing scheme (RFC0932)

IP.com Disclosure Number: IPCOM000004346D
Original Publication Date: 1985-Jan-01
Included in the Prior Art Database: 2000-Oct-10
Document File: 3 page(s) / 9K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

D.D. Clark: AUTHOR

Abstract

Several recent RFCs have discussed the need for a "subnet" structure within the internet addressing scheme, and have proposed strategies for "subnetwork" addressing and routing. In particular, Jeff Mogul in his RFC-917, "Internet Subnets", describes an addressing scheme in which a variable number of the leading bits of the host portion of the address are used to identify the subnet. The drawback to this scheme is that it is necessary to modify the host implementation in order to implement it. While the modification is a simple one, it is necessary to retrofit it into all implementations, including those which are already in the field. (See RFC-917 by Mogul for various alternative approaches to this problem, such as using Address Resolution Protocol.)

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 33% of the total text.

Network Working Group David D. Clark

Request for Comments: 932 MIT, LCS

January 1985

A SUBNETWORK ADDRESSING SCHEME

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.

INTRODUCTION

Several recent RFCs have discussed the need for a "subnet" structure

within the internet addressing scheme, and have proposed strategies

for "subnetwork" addressing and routing. In particular, Jeff Mogul

in his RFC-917, "Internet Subnets", describes an addressing scheme in

which a variable number of the leading bits of the host portion of

the address are used to identify the subnet. The drawback to this

scheme is that it is necessary to modify the host implementation in

order to implement it. While the modification is a simple one, it is

necessary to retrofit it into all implementations, including those

which are already in the field. (See RFC-917 by Mogul for various

alternative approaches to this problem, such as using Address

Resolution Protocol.)

This RFC proposes an alternative addressing scheme for subnets which,

in most cases, requires no modification to host software whatsoever.

The drawbacks of this scheme are that the total number of subnets in

any one network are limited, and that modification is required to all

gateways.

THE PROPOSAL

In this scheme, the individual subnets of a network are numbered

using Class C addresses. Since it is necessary with this scheme that

a Class C address used to number a subnet be distinguishable from a

Class C address used to number an isolated network, we will reserve

for subnetworks the upper half of the Class C address space, in other

words all those Class C addresses for which the high order bit is on.

When a network is to be organized as a series of subnetworks, a block

of these reserved Class C addresses will be assigned to that network,

specifically a block of 256 addresses having the two first bytes

identical. Thus, the various subnetworks of a network are

distinguished by the third byte of the Internet address. (This

addressing scheme implies the limitation that there can only be 256

subnetworks in a net. If more networks are required, two blocks will

have to be allocated, and the total viewed as two separate networks.)

RFC 932 January 1985

A Subnetwork Addressing Scheme

The gateways and hosts attached to this subnetted network use these

addresses as ordinary Class C addresses. Thus, no modification to

any host software is required for hosts attached to a subnetwork.

For gateways not directly attached to the subnetted network, it is an

unacceptable burden to separately store the routing information to

e...