How is OSPF external route summarization different from inter-area summarization?

OSPF external route summarization is specifically associated with external routes that are introduced into the OSPF domain via Autonomous System Boundary Routers (ASBRs). When an ASBR receives a route from outside the OSPF routing domain, it can summarize those routes, which reduces the amount of data that must be exchanged among OSPF routers and optimizes routing table usage.

Performing summarization on an ASBR is beneficial because it allows for more efficient routing by consolidating multiple external routes into a single summary route. This minimizes the number of entries in the OSPF database and lessens the complexity of OSPF routing, enhancing overall performance.

In contrast, inter-area summarization involves summarizing routes between different OSPF areas, and it is typically done on Area Border Routers (ABRs). This distinction is critical when considering how OSPF manages external versus internal routes. Therefore, option C accurately describes this unique capability of ASBRs to summarize external routes, differentiating it from the function of ABRs concerning inter-area summarization.