RFC 1793 (rfc1793) - Page 1 of 32

Extending OSPF to Support Demand Circuits

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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-



Moy
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