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draft-pillay-esnault-ospf-flooding-07.txt --> rfc4136.txt

Network Working Group Padma P. Pillay-Esnault
Internet Draft Juniper Networks
June 2003
Request for Comments: 4136 Cisco Systems
Category: Informational
Expires: December 2003 July 2005

OSPF Refresh and Flooding Reduction in Stable Topologies

draft-pillay-esnault-ospf-flooding-07.txt

Status of this This Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

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1. (2005).

Abstract

This document describes an extension to the OSPF protocol to reduce
periodic flooding of Link State Advertisements (LSAs) in stable
topologies.

The

Current OSPF current behavior requires that all LSAs other than LSAs, except DoNotAge
LSAs LSAs,
to be refreshed every 30 minutes. This document proposes to
generalize the use of DoNotAge LSAs in order to reduce protocol
traffic in stable topologies

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2. Motivation topologies.

1. Introduction

The explosive growth of IP based IP-based networks has placed focus on the
scalability of Interior Gateway Protocols such as OSPF. Networks
using OSPF are growing every day and will continue to expand to
accommodate the demand for connections to the Internet or intranets.

Internet Service Providers and users having that have large networks have
noticed non-negligible protocol traffic traffic, even when their network
topologies were stable.

OSPF requires every LSA to be refreshed every 1800 seconds or else
they will expire when they reach 3600 seconds [1].

This document proposes to overcome the LSA expiration by generalizing
the use of DoNotAge LSAs. This technique will facilitate OSPF
scaling by reducing OSPF traffic overhead in stable topologies.

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2. Changes in the existing implementation. Existing Implementation

This enhancement relies on the implementation of the DoNotAge bit and
the Indication-LSA. The details of the implementation of the
DoNotAge bit and the Indication-LSA are specified in "Extending OSPF
to Support Demand Circuits" [2].

Flooding reduction capable

Flooding-reduction-capable routers will continue to send hellos to
their neighbors and keep aging their self-originated LSAs in their
database. However, they these routers will flood their self-originated
LSAs with the DoNotAge bit set. Hence, Thus, self-originated LSAs do not
have to be reflooded re-flooded every 30 minutes and the reflooding re-flooding interval
can be extended to the configured forced flooding forced-flooding interval. As in
normal OSPF operation, any change in the contents of the LSA will
cause a reoriginated LSA to be flooded with the DoNotAge bit set.
This will reduce protocol traffic overhead while allowing changes to
be flooded immediately.

Flooding reduction capable

Flooding-reduction-capable routers will flood received
non-self-originated non-self-
originated LSAs with the DoNotAge bit set on all normal or flooding-reduction only flooding-
reduction-only interfaces within the LSA's flooding scope. If an
interface is configured both as flooding-reduction
capable both flooding-reduction-capable and Demand-Circuit
Demand-Circuit, then the flooding is done if and only if the contents
of the LSA have changed. This allows LSA flooding for unchanged LSAs
to be periodically forced by the originating router.

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3. Backward Compatibility

Routers supporting the demand circuit extensions [2] will be able to
correctly process DoNotAge LSAs flooded by routers supporting the
flooding reduction capability described herein. These routers will
also suppress flooding DoNotAge LSAs on interfaces configured as
demand circuits. However, they will also flood DoNotAge LSAs on
interfaces which that are not configured as demand circuits.

When there are routers in the OSPF routing domain, stub area, or NSSA area
area, that do not support the demand circuit extensions [2] then the
use of these flooding reduction capability capabilities will be subject to the
demand circuit interoperability constraints articulated in section
2.5 of "Extending OSPF to Support Demand Circuits" [2]. This implies
that detection of an LSA LSA, with the DC bit clear clear, will result in the
re-origination of self-originated DoNotAge LSAs with the DoNotAge
clear and purging of non-self-originated DoNotAge LSAs.

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4. Security Considerations

This memo does not create any new security issues for the OSPF
protocol. Security considerations for the base OSPF protocol are
covered in [1].

6. Intellectual Property Considerations

The IETF has been notified by Cisco Systems of intellectual property
rights claimed in regard to some or all of the specifications
contained in this document. For more information please refer to the
IETF web page http://www.ietf.org/ietf/IPR/CISCO-OSPF-REFRESH.txt

5. Acknowledgments

The author would like to thank Jean-Michel Esnault, Barry Friedman,
Thomas Kramer, Acee Lindem, Peter Psenak, Henk Smit Smit, and Alex Zinin
for their helpful comments on this work.

6. Normative References

[1] RFC 2328 OSPF Moy, J., "OSPF Version 2. J. Moy. 2", STD 54, RFC 2328, April 1998.

[2] RFC 1793 Extending Moy, J., "Extending OSPF to Support Demand Circuits. J. Moy. Circuits", RFC 1793,
April 1995.

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RFC 4136 OSPF Refresh and Flooding Reduction March 2003 July 2005

A. Configurable Parameters

This memo defines new configuration parameters for the flooding
reduction feature. The feature must be enabled by configuration on a
router and is is, by default default, off.

flooding-reduction <all | list of interfaces> Indicates that the
router has the flooding reduction feature enabled. By default, it
this parameter applies to all interfaces running under the OSPF
instance to which it applies. The feature can be enabled on a
subset of explicitly specified interfaces.

flooding-interval <n minutes> Indicates the interval in minutes for
the periodic flooding of self-originated LSAs. By default default, this
value is 30 minutes as per [1]. The minimum value is also 30
minutes. A value of infinity will prevent reflooding re-flooding of self-originated self-
originated LSAs that have not changed.

Author's Address

Padma Pillay-Esnault
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134

EMail: ppe@cisco.com

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9. Authors' Addresses

Padma Pillay-Esnault
Juniper Networks
1194 N, Mathilda Avenue
Sunnyvale, CA 94089-1206

Email: padma@juniper.net July 2005

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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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