CCNP Routing and Switching ROUTE 300-101 Official Cert Guide

Manual Summarization at ASBRs

Lesson 6: Type 5 LSA: External

OSPF defines an ASBR as a router that redistributes routes into OSPF from some other routing sources. When redistributing the routes, the ASBR creates a Type 5 External LSA for each redistributed subnet, listing the subnet number as the LSID and listing the mask as one of the fields in the LSA. The LSA also lists the ASBR’s RID as the advertising router and a cost metric for the route. For the purposes of route summarization, you can think of a Type 5 LSA as working much like a Type 3 LSA, except for routes learned externally.

This section describes ASBR route summarization, which has ...