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Network Working Group Padma Pillay-Esnault
Internet Draft Juniper Networks
January
March 2003
Category: Standards Track
Expires: June October 2003
OSPF Refresh and Flooding Reduction in Stable Topologies
draft-pillay-esnault-ospf-flooding-04.txt
draft-pillay-esnault-ospf-flooding-05.txt
Status of 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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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
1. Abstract
This document describes an extension to the OSPF protocol to
eliminate or reduce periodic flooding of Link State Advertisements
in stable topologies.
The current behavior of OSPF requires that all LSAs be refreshed
every 30 minutes regardless of the stability of the network except
for DoNotAge LSAs. This document proposes to generalize the use of
DoNotAge LSAs so as to reduce protocol traffic in stable topologies.
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Internet Draft OSPF Refresh and Flooding Reduction January March 2003
2. Motivation
The explosive growth of IP based networks has placed the focus on the
scalability of the Interior Gateway Protocols such as OSPF. Networks
using OSPF are larger everyday growing every day and will continue to expand to
accommodate the demand to connect for connections to the Internet or intranets.
Internet Service Providers and users having large networks have
noticed non-negligible protocol traffic even when their network
topology was
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.
3. Changes in the existing implementation.
This enhancement relies heavily on the OSPF Demand Circuit extension.
The details of the implementation of the DC-bit, DoNotAge bit and
the Indication-LSA are specified in "Extending OSPF to Support
Demand Circuits" [2].
The Flooding Reduction flooding reduction capable routers will continue to send hellos
to their neighbors but and keep their aging self-originated LSAs in
their database. However, they will flood their Link State Advertisements
(LSAs) self-originated LSAs
with the DoNotAge bit set. Hence, self-originated LSAs need not be
reflooded unless there is change in the contents of the LSA. This
will reduce the protocol traffic overhead while allowing changes to
be flooded immediately.
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4. Deployment
4.1 Backward Compatibility
Routers supporting the OSPF Demand Circuit capability.
All routers supporting OSPF Demand Circuit demand circuit extensions [2] will be
able to
interoperate with the correctly process DoNotAge LSAs flooded by routers
supporting the flooding reduction.
For routers supporting OSPF Demand Circuits but do NOT support the
new Flooding Reduction reduction capability but have to interoperate with described herein.
These routers having the Flooding Reduction capability there are two
possibilities:
(1) Demand Circuit is not configured
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 will however receive also suppress flooding DoNotAge LSAs from the
flooding reduction capable routers and will keep them as such in
its own database.
(2) Demand Circuit is on
interfaces configured
All DC routers as demand circuits. However, they will set the DoNotAge bit also
flood DoNotLSAs on their own LSAs and will
suppress hellos. The flooding reduction capable routers will run as
DC as well.
4.2 Router interfaces which are not supporting configured as demand
circuits.
When there are routers in the OSPF Demand Circuit capability.
For routers routing domain, stub area,
or NSSA area that do not support OSPF Demand Circuit Feature have no
knowledge how to handle DoNotAge LSAs and the LSAs with demand circuit extensions [2]
then the DoNotAge
bit set use of these flooding reduction capability will appear as expired LSAs in their own database.
The DCbitless LSAs must be used here
subject to detect the presence demand circuit interoperability constraints
articulated in section 2.5 of those
routers not supporting the "Extending OSPF to Support Demand Circuit and indication LSAs
Circuits" [2]. This implies that detection of an LSA with the DC
bit clear will be use as described result in [2] to inform other routers of the
presence re-origination of routers incapable to handling self-originated
DoNotAge LSAs. In the
presence of routers not supporting DC-bit, the Flooding Reduction
capable routers must flush all LSAs with the DoNotAge LSAs clear and revert to
sending normal aging purging of
non-self-originated DoNotAge LSAs.
5. Configuration of the Flooding Reduction flooding reduction capable routers
The implementations
Implementations of Flooding Reduction this flooding reduction capability must provide a
knob to activate/deactivate the feature and by default it should be
disabled. It should be also The flooding reduction capability can be enabled globally
or on selected interfaces. It should be also possible to specify a
forced periodic
refresh flooding interval of Link State Advertisements.
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Internet Draft OSPF Refresh and Flooding Reduction January 2003 unchanged self-originated LSAs.
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].
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7. Acknowledgments
The author would like to thank Jean-Michel Esnault, Barry Friedman,
Thomas Kramer, Acee Lindem, Peter Psenak and Psenak, Henk Smit and Alex Zinin
for their helpful comments on this work.
8. Normative References
[1] RFC 2328 OSPF Version 2. J. Moy. April 1998.
[2] RFC 1793 Extending OSPF to Support Demand Circuits. J. Moy.
April 1995.
9. Authors' Addresses
Padma Pillay-Esnault
Juniper Networks
1194 N, Mathilda Avenue
Sunnyvale, CA 94089-1206
Email: padma@juniper.net
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Internet Draft OSPF Refresh and Flooding Reduction January 2003
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