BGP Route Summarization

Question 1

What is BGP Address Summarization/Route Aggregation (RA)?

Answer 1

BGP Address summarization/Route Aggregation (RA), is a method to minimize the size of the routing table by announcing the whole address block received from a peer router.

Question 2

What are the benefits of BGP Address summarization/Route Aggregation (RA)?

Answer 2

1. BGP Address summarization can help conserve router resources.
2. Accelerate best path calculation by reducing the size of the routing table.

Question 3

What are the two techniques for BGP summarization or Route Aggregation (RA)?

Answer 3

There are two techniques for BGP summarization: static and dynamic.

1. Static: A static route to Null 0 is created for the prefix, and then the network is advertised via a network statement. The downfall of this technique is that the summary route will always be advertised even if the networks are unavailable.
2. Dynamic: The aggregate-address command summarizes the routes for the network. The summary-only keyword specifies that only the summary route should be advertised, not the more specific routes.

router bgp 65100
network X.X.X.X mask X.X.X.X
aggregate-address X.X.X.X X.X.X.X summary-only

Question 4

What happens when an aggregate route is created?

Answer 4

When an aggregate route is created, a new network prefix with a shorter prefix length is advertised into BGP.

Question 5

What are some considerations when using BGP Address summarization?

Answer 5

When using BGP Address summarization, it’s important to consider the following:

• What network to summarized.
• Static summarization
• Dynamic summarization.