Network Design and Operations
On the internet, which protocol exchanges routing information between the networks run by organizations such as ISPs (ASes, autonomous systems) and chooses routes based on attributes such as the sequence of ASes a route has passed through (AS_PATH) and on each organization's policy?
- AOSPF
- BBGP
- CRIP
Show answer and explanation
Answer: B. BGP
BGP (Border Gateway Protocol) is the protocol that organizations identified by AS numbers use to exchange routes, and routes on the internet are basically exchanged with BGP. Routes carry attributes such as the sequence of ASes they have passed through (AS_PATH) and the next hop (NEXT_HOP), and a router prevents loops by discarding routes that contain its own AS number. Route selection is not just a matter of the shortest AS_PATH; an organization's policies, such as which neighbor to prefer, can be expressed in attributes and applied. OSPF and RIP are routing protocols used inside a single organization (IGPs).
- A. OSPF is a protocol that computes shortest paths inside an organization from the state of its links.
- B. Correct. It is the protocol used to exchange routes between ASes.
- C. RIP is a distance-vector protocol that chooses routes by hop count inside an organization.