Individual Vishwas Manral
Internet-Draft SiNett Corp.
Expires: May 30, 2005
November 30, 2004
Treating unknown Router-LSA link types
draft-manral-ospf-router-lsa-unknown-type-01
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Copyright (C) The Internet Society (2004).
Abstract
This document attempts to discuss and clarify the text in [OSPFv2] and
[OSPFv3], about dealing with unknown link types in router LSA's.
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1. Problem Definition
The text in [OSPFv2] and [OSPFv3] does not state how to treat unknown
link types when present in Router LSA's.
Link-state Routing assumes that an OSPF router maintains an identical
database describing the Autonomous System's topology. Incase the a
Router LSA with an unknown link type is received implementations treat
the LSA differently. While some implementations can ignore the link
yet process the rest of the LSA others can simply ignore the LSA. This
leads to different databases in the routers and hence different routing
tables.
2. Changes for OSPFv2
Section 12.4.1 [OSPFv2] describes the various values used to Link-types
in Router LSA's. The values 1, 2, 3 and 4 are defined.
If a Router LSA with an unknown link-type is being processed, the link
is ignored and the rest of the router LSA is processed normally.
Section 16.1 (2)(a) [OSPFv2] should now read
If this is a link to a stub network, examine the next
link in V's LSA. Links to stub networks will be
considered in the second stage of the shortest path
calculation. If the link type is unknown examine the
next link in V's LSA. Unknown Link Types are ignored.
3. Changes for OSPFv3
Section A.4.3 [OSPFv3] described the various values of Link-types in
Router LSA's/ The values 1, 2 and 4 are defined to be used in routing
table calculations, while 3 is reserved.
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If a Router-LSA with an unknown or reserved link-type is being processed,
the link is ignored and the rest of the router LSA is processed normally.
Section 3.8.1 [OSPFv3] remains unchanged as it Refers to Section 16.1,
[OSPFv2].
4. Future Extensions to Link-type
As the behavior for treating an unknown Link-type is defined, extensions to
Link-type are now possible.
Any future extensions SHOULD not cause any change in routing table
calculations. Such a change can result in routing loops because the routers
unaware of the extension will ignore the link.
5. Security Considerations
This document doesn't raise any new security concerns other than
those covered in [OSPFv2] and [OSPFv3].
6. IANA Considerations
This document doesn't raise any new IANA considerations.
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7. Normative References
[OSPFv2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[OSPFv3] Moy, J., Ferguson, D. and R. Colton, "OSPF for IPv6", RFC
2740, December 1999.
Authors' Addresses
Vishwas Manral
SiNett Corp
Bangalore
India
EMail: vishwas@sinett.com
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Appendix A. Acknowledgments
Many thanks to Acee Lindem, Tony Przygienda, Padma P. and Sina Mirtorabi
for initiating the discussion.
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