What type of protocol is BGP and what does it exchange?

• A. It is an interior gateway protocol used inside a single autonomous system.
• B. It is a link-state protocol used for rapid convergence.
• C. It is a distance-vector protocol used for campus networks.
• D. It is an exterior gateway protocol that exchanges routing information between autonomous systems.

Answer: (D)

BGP is an exterior gateway protocol. It operates at the edge of networks and exchanges routing information between autonomous systems, i.e., different networks under separate administrative control. It shares which IP prefixes are reachable across AS boundaries and the path information that led to those prefixes, using NLRI (prefix reachability) along with path attributes like AS_PATH and NEXT_HOP. This mechanism is what enables policy-based routing decisions between different organizations’ networks. It’s not used inside a single AS (that’s what interior gateway protocols handle), and it isn’t a link-state or traditional distance-vector protocol.