Which two statements are true about route summarization? (Choose two.)

Route summarization, or route aggregation, is a core technique for improving the scalability of routing protocols. Its primary benefit is reducing the number of entries in a router's routing table by advertising a single, less-specific summary route in place of multiple, more-specific routes. This directly leads to smaller routing tables, which consume less memory and processing power. A crucial secondary benefit is enhanced network stability. By summarizing routes, individual link failures within the aggregated address block are not advertised to the rest of the network, thus reducing the volume of routing update messages (signaling) and preventing route flapping from propagating.

C. It summaries the routing table entries into a default route

This is incorrect because summarization creates a less-specific route (a supernet), which is not necessarily a default route (0.0.0.0/0). A default route is only one specific type of summary.

D. It improves the best route calculation.

This is incorrect. Summarization can hide details about the network topology, which may lead to suboptimal routing decisions, as a router may not have the more-specific prefix information needed to choose the truly best path.

1. Kurose

J. F.

& Ross

K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson.

Section 5.3.2

"Hierarchical Routing": This section explains that route aggregation is a key feature of hierarchical routing. It states

"routers in the backbone need not know about every router within a region... This ability to aggregate routes and hide details of the network topology is key to creating scalable routing protocols." This supports the reduction of routing table size (A) and reduction of signaling (B).

2. Cisco Systems

Inc. (2005). IP Routing: OSPF Design Guide.

Section: "Summarization": "The main advantages of summarization are that it reduces the size of the routing table... and it helps to contain routing information

so if a link is flapping

the flapping is not propagated into the backbone." This directly validates that summarization reduces routing table size (A) and signaling (B).

3. Halabi

B. (2000). Internet Routing Architectures (2nd ed.). Cisco Press.

Chapter 4

"Tuning BGP Capabilities"

Section: "Route Aggregation": The text describes aggregation as a mechanism to "reduce the amount of routing information that is passed around." It explicitly mentions that a major benefit is "insulating a routing domain from instabilities" that occur in another domain

which directly corresponds to reducing signaling (B). It also states aggregation's purpose is to keep routing tables "at a manageable size" (A).