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Another Internet subnet addressing scheme (RFC0936)

IP.com Disclosure Number: IPCOM000004352D
Original Publication Date: 1985-Feb-01
Included in the Prior Art Database: 2000-Oct-11
Document File: 4 page(s) / 10K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

M.J. Karels: AUTHOR

Abstract

There have been several proposals for schemes to allow the use of a single Internet network number to refer to a collection of physical networks under common administration which are reachable from the rest of the Internet by a common route. Such schemes allow a simplified view of an otherwise complicated topology from hosts and gateways outside of this collection. They allow the complexity of the number and type of these networks, and routing to them, to be localized. Additions and changes in configuration thus cause no detectable change, and no interruption of service, due to slow propagation of routing and other information outside of the local environment. These schemes also simplify the administration of the network, as changes do not require allocation of new network numbers for each new cable installed. The motivation for explicit or implicit subnets, several of the alternatives, and descriptions of existing implementations of this type have been described in detail [1,2]. This proposal discusses an alternative scheme, one that has been in use at the University of California, Berkeley since April 1984.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 30% of the total text.

Network Working Group Michael J. Karels

Request for Comments: 936 UC Berkeley

February 1985

Another Internet Subnet 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

There have been several proposals for schemes to allow the use of a

single Internet network number to refer to a collection of physical

networks under common administration which are reachable from the

rest of the Internet by a common route. Such schemes allow a

simplified view of an otherwise complicated topology from hosts and

gateways outside of this collection. They allow the complexity of

the number and type of these networks, and routing to them, to be

localized. Additions and changes in configuration thus cause no

detectable change, and no interruption of service, due to slow

propagation of routing and other information outside of the local

environment. These schemes also simplify the administration of the

network, as changes do not require allocation of new network numbers

for each new cable installed. The motivation for explicit or

implicit subnets, several of the alternatives, and descriptions of

existing implementations of this type have been described in detail

[1,2]. This proposal discusses an alternative scheme, one that has

been in use at the University of California, Berkeley since

April 1984.

Subnet Addressing at Berkeley

As in the proposal by Jeff Mogul in RFC-917, the Berkeley subnet

addressing utilizes encoding of the host part of the Internet

address. Hosts and gateways on the local network are able to

determine the subnet number from each local address, and then route

local packets based on the subnet number. Logically, the collection

of subnets appears to external sites to be a single, homogenous

network. Internally, however, each subnet is distinguished from the

others and from other networks, and internal routing decisions are

based on the subnet rather than the network number.

The encoding of subnet addresses is similar to that proposed in

RFC-917. In decomposing an Internet address into the network and

host parts, the algorithm is modified if the network is "local", that

is, if the network is a directly-connected network under local

administrative control. (Networks are marked as local or non-local

RFC 936 February 1985

Another Internet Subnet Addressing Scheme

at the time each network interface's address is set at boot time.)

For local addresses, the host part is examined for a subnet number.

Local addresses may be on the main network, or they may be on a

subnet. The high-order bit of the host number is used to disting...