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Extending OSPF to Support Demand Circuits (RFC1793)

IP.com Disclosure Number: IPCOM000004047D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 25 page(s) / 73K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Moy: AUTHOR

Abstract

This memo defines enhancements to the OSPF protocol that allow efficient operation over "demand circuits". Demand circuits are network segments whose costs vary with usage; charges can be based both on connect time and on bytes/packets transmitted. Examples of demand circuits include ISDN circuits, X.25 SVCs, and dial-up lines. The periodic nature of OSPF routing traffic has until now required a demand circuit's underlying data-link connection to be constantly open, resulting in unwanted usage charges. With the modifications described herein, OSPF Hellos and the refresh of OSPF routing information are suppressed on demand circuits, allowing the underlying data-link connections to be closed when not carrying application traffic.

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Network Working Group J. Moy

Request for Comments: 1793 Cascade

Category: Standards Track April 1995

Extending OSPF to Support Demand Circuits

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Abstract

This memo defines enhancements to the OSPF protocol that allow

efficient operation over "demand circuits". Demand circuits are

network segments whose costs vary with usage; charges can be based

both on connect time and on bytes/packets transmitted. Examples of

demand circuits include ISDN circuits, X.25 SVCs, and dial-up lines.

The periodic nature of OSPF routing traffic has until now required a

demand circuit's underlying data-link connection to be constantly

open, resulting in unwanted usage charges. With the modifications

described herein, OSPF Hellos and the refresh of OSPF routing

information are suppressed on demand circuits, allowing the

underlying data-link connections to be closed when not carrying

application traffic.

Demand circuits and regular network segments (e.g., leased lines) are

allowed to be combined in any manner. In other words, there are no

topological restrictions on the demand circuit support. However,

while any OSPF network segment can be defined as a demand circuit,

only point-to-point networks receive the full benefit. When broadcast

and NBMA networks are declared demand circuits, routing update

traffic is reduced but the periodic sending of Hellos is not, which

in effect still requires that the data-link connections remain

constantly open.

While mainly intended for use with cost-conscious network links such

as ISDN, X.25 and dial-up, the modifications in this memo may also

prove useful over bandwidth-limited network links such as slow-speed

leased lines and packet radio.

The enhancements defined in this memo are backward-compatible with

the OSPF specification defined in [1], and with the OSPF extensions

defined in [3] (OSPF NSSA areas), [4] (MOSPF) and [8] (OSPF Point-

to-MultiPoint Interface).

This memo provides functionality similar to that specified for RIP in

[2], with the main difference being the way the two proposals handle

oversubscription (see Sections 4.3 and 7 below). However, because

OSPF employs link-state routing technology as opposed to RIP's

Distance Vector base, the mechanisms used to achieve the demand

circuit functionality are quite different.

Please send comments to ospf@gated.cornell.edu.

Acknowledgments

The author would like to acknowledge the helpful comments of Fred

Baker, Rob Coltun, ...