BGP Prefix list

Question 1

What is a BGP Prefix list?

Answer 1

A BGP Prefix list is a configuration to filter routing updates based on a permit or deny, which is applied to updates to and from neighbors.

ip prefix-list LIST permit 192.168.1.0/24
!
router bgp 65001
neighbor 192.168.2.1 prefix-list LIST out

Question 2

How does a BGP Prefix list work?

Answer 2

• The prefix list can permit or deny a matching network and netmasks.
• The prefix list can be applied to a BGP neighbor.
• The prefix list can be applied in any direction, either inbound or outbound.

Question 3

What is the difference between a BGP Prefix list and a Distribute list?

Answer 3

• A BGP Prefix list performs route filtering based on IP network addresses and netmasks of advertised routes.
• A Distribute list performs route filtering based on an access list or prefix list.

Question 4

How do I configure a BGP Prefix list?

Answer 4

ip prefix-list NAME permit/deny 192.168.1.0/24
!
router bgp 65001
neighbor 192.168.2.1 prefix-list NAME in/out

Question 5

What are some considerations when using a BGP Prefix list?

Answer 5

• What prefix to permit or deny.
• Which neighbors to apply the prefix list.
• Direction: inbound or outbound.