By default, OSPF does not perform automatic route summarization. Instead, OSPF-enabled routers must be manually configured to summarize routes. In Cisco IOS software, different commands must be used to summarize internal and external routing information. The following sections describe both types of route summarization and delve into the specifics on each type of summary and how it is propagated throughout the OSPF domain.
Internal route summarization
In OSPF, ABRs are responsible for generating a single Type 3 Summary LSA for each intra-area route, i.e. Type 1 and Type 2 LSA, within their area. These LSAs . . .
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