OSPF Route Summarization

BCD.

OSPF (Open Shortest Path First) is a link-state routing protocol that uses cost as a metric for determining the shortest path to a destination network. Route summarization is a technique used to simplify the routing table by aggregating multiple prefixes into a single prefix. This reduces the size of the routing table and can lead to a more stable network.

The correct answers are A, B, and D.

A. OSPF routes can be summarized at any OSPF router in the network using area range or summary address commands. Route summarization can be done in OSPF by using either the "area range" command to summarize routes within an OSPF area or the "summary-address" command to summarize routes between OSPF areas.

B. OSPF internal routes can be summarized only at the ABRs. OSPF internal routes can only be summarized at the Area Border Routers (ABRs), which are the routers that connect multiple OSPF areas.

C. OSPF type 5 external routes can be summarized only at the ASBRs. OSPF Type 5 External routes are generated by AS Boundary Routers (ASBRs) and are advertised throughout the OSPF domain. They can only be summarized at the ASBRs.

D. Route summarization can lead to a more stable network. By summarizing routes, the routing table size is reduced, which reduces the amount of CPU and memory usage on the routers. This can lead to a more stable network because there is less chance of the router running out of resources.

E. OSPF internal routes are automatically summarized via type 3 summary LSAs. OSPF internal routes are automatically summarized within an OSPF area via Type 3 summary Link State Advertisements (LSAs). This summarization is based on the network boundaries of the OSPF area.

F. A flat addressing scheme is required in order to summarize OSPF routes. OSPF route summarization does not require a flat addressing scheme. However, it is important to consider the summarization carefully to ensure that there are no unintended consequences, such as loss of granularity in the routing table.