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OSPF Complete Implementation by John T. Moy

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10. OSPF Hierarchy

The OSPF protocol supports multiple levels of hierarchy, first allowing the OSPF routing domain to be broken up into regions, or areas, and then allowing external routing information to be imported into the OSPF routing domain in AS-external-LSAs. This chapter discusses OSPF area routing: the rules for configuring areas, aggregation of routing information at area boundaries, virtual links, and the interaction of summary-LSAs and the OSPF routing calculations. We also discuss the handling of external routing information, including the origination of AS-external-LSAs, the external routing calculation, and the interaction between OSPF areas and external routes.

10.1. Guidelines for Area Boundaries

Many people are confused about ...

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