How does OSPF handle route summarization?

OSPF handles route summarization primarily at the Area Border Routers (ABRs) and Autonomous System Boundary Routers (ASBRs) through the use of summary Link State Advertisements (LSAs). The process of summarizing routes allows OSPF to reduce the size of the routing table by allowing multiple contiguous IP prefixes to be advertised as a single summary route, thus optimizing routing efficiency and reducing overhead.

ABRs are responsible for summarizing routes from one area before advertising them to another area. This minimizes the amount of information exchanged between areas, which is particularly important in larger networks where numerous subnets might exist. ASBRs summarize routes when exchanging routes between different routing protocols or external networks.

This function is not performed automatically; it requires manual configuration to define which routes should be summarized. Additionally, it does not occur solely at the router level or the link layer, as it is specifically concerned with how information is propagated between OSPF areas and how external routes are introduced to OSPF. Thus, summarization is a critical aspect of OSPF optimization facilitated through summary LSAs at ABRs and ASBRs.