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draft-pillay-esnault-ospf-flooding-03.txt --> draft-pillay-esnault-ospf-flooding-04.txt

Network Working Group Padma Pillay-Esnault
Internet Draft Juniper Networks
Expiration Date:June 2001 December 2000
January 2003
Category: Standards Track
Expires: June 2003

OSPF Refresh and flooding reduction Flooding Reduction in stable topologies

draft-pillay-esnault-ospf-flooding-03.txt Stable Topologies

draft-pillay-esnault-ospf-flooding-04.txt

Status of this Memo

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1. Abstract

This document describes extension to the OSPF protocol [1] to
optimize eliminate
or reduce periodic flooding of Link State Advertisements (LSA) in stable
topologies.

The current behavior of OSPF requires that all LSA LSAs be refreshed
every 30 minutes regardless of the stability of the network except
for Do Not Age (DNA) LSA [2]. DoNotAge LSAs. This document proposes to generalize the use of DNA LSA
DoNotAge LSAs so as to reduce protocol traffic in stable
networks. topologies.

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2. Motivation

The explosive growth of IP based networks has placed the focus on the
scalability of the Interior Gateway Protocols such as OSPF. The
networks Networks
using OSPF are larger everyday and will continue to expand to
accommodate the demand to connect to the Internet or intra nets. intranets.

Internet Service Providers and users having large networks have
noticed of a non negligible non-negligible protocol traffic even when their network
topology was stable.

By design

OSPF requires every LSA to be refreshed as every 1800 seconds or else
they will expire after when they reach 3600 seconds. Some implementations have tried to improve the flooding
by reducing its frequency to refresh from 30 minutes to around 50 minutes
or so. This solution presents the advantage of cutting down the amount
of refresh traffic but will require at least one refresh before the LSA
expires. seconds [1].

This document proposes to overcome the LSA expiration by implementing generalizing
the generalization use of DO NOT AGE LSA use. By DoNotAge LSAs. This technique will facilitate OSPF
scaling by reducing considerably the OSPF traffic overhead in stable topologies OSPF will scale better. topologies.

3. Changes in the existing implementation.

The existing

This enhancement relies heavily on the OSPF Demand Circuit feature [2] provides the premise extension.
The details of the
Do Not Age LSA implementation.

The goal here is to reduce refreshing and flooding implementation of already known the DC-bit, DoNotAge bit and unchanged information. To achieve this,
the Indication-LSA are specified in "Extending OSPF to Support
Demand Circuits" [2].

The Flooding Reduction capable routers will continue to send hellos
to their neighbors but will flood their Link State Advertisements
(LSAs) with the DoNotAge bit set. This will now reduce the protocol
traffic overhead while allowing changes to be flooded over all interfaces immediately.

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Internet Draft OSPF Refresh and Flooding Reduction January 2003

4. Deployment

4.1 Routers supporting the OSPF Demand Circuit capability.

All routers supporting OSPF Demand Circuit will be able to
interoperate with the higher bit set thus
making them DO routers supporting the flooding reduction.

For routers supporting OSPF Demand Circuits but do NOT AGE LSAs.

The LSA originator can then set support the refresh rate
new Flooding Reduction capability but have to what ever it interoperate with
routers having the Flooding Reduction capability there are two
possibilities:

(1) Demand Circuit is not configured to.
In this case, the router older implementation will send its LSAs
without the DoNotAge bit set and it will need to refresh its LSAs
periodically. It can be will however receive DoNotAge LSAs from the
flooding reduction capable routers and will keep them as such in
its own database.

(2) Demand Circuit is configured for periodic refresh over
extended periods (days, weeks or months) or even never at all.
All the DC routers should implement will set the DoNotAge bit on their own LSAs and will
suppress hellos. The flooding reduction capable routers will run as defined by
Section 2 of RFC 1793.

4. Security Considerations

This memo does
DC as well.

4.2 Router not create any new security issues for supporting the OSPF
protocol. Security considerations for the base Demand Circuit capability.

For routers that do not support OSPF protocol are
covered Demand Circuit Feature have no
knowledge how to handle DoNotAge LSAs and the LSAs with the DoNotAge
bit set will appear as expired LSAs in [Ref1]. their own database.

The enhancement rely heavily on DCbitless LSAs must be used here to detect the presence of those
routers not supporting the OSPF Demand Circuit mechanism and come at
the same costs indication LSAs
will be use as described in [2] section 6. to inform other routers of the
presence of routers incapable to handling DoNotAge LSAs. In the
presence of routers not supporting DC-bit, the Flooding Reduction
capable routers must flush all the DoNotAge LSAs and revert to
sending normal aging LSAs.

5. Configuration of the Flooding Reduction capable routers

The implementations of Flooding Reduction capability must provide a
knob to activate/deactivate the feature and by default it should be
disabled. It should be also possible to specify a forced periodic
refresh interval of Link State Advertisements.

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5. OSPF Refresh and Flooding Reduction January 2003

6. 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].

7. Acknowledgments

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

8. Normative References

[1] RFC 2328 OSPF Version 2. J. Moy. April 1998. (Format: TXT=447367
bytes) (Obsoletes RFC2178) (Also STD0054) (Status: STANDARD)

[2] RFC 1793 Extending OSPF to Support Demand Circuits. J. Moy.
April 1995. (Format: TXT=78728 bytes) (Status: PROPOSED STANDARD)

9. Authors' Addresses

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

Email: padma@juniper.net

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