Which statement describes how BGP exchanges routing information with neighbors?

• A. BGP exchanges routes using UDP broadcasts.
• B. BGP forms a TCP session with neighbors to exchange routing information.
• C. BGP uses ICMP messages to propagate routes.
• D. BGP relies solely on static routes for exchange.

Answer: (B)

BGP exchanges routing information by establishing a TCP session between each pair of neighbors and sending updates over that reliable connection. This session-based approach is why BGP uses TCP rather than a connectionless transport: TCP provides ordered delivery, reliability, and flow control, which are essential for the correct propagation of complex routing policies. After the TCP handshake, neighbors exchange OPEN messages to set up parameters, UPDATE messages that carry the actual routes plus path attributes (like AS_PATH and NEXT_HOP), KEEPALIVE messages to maintain the session, and NOTIFICATION messages if an error occurs. The communication typically happens over port 179.

Because updates rely on a persistent TCP session, UDP broadcasts aren’t used to carry BGP routing information, and ICMP isn’t used to propagate routes. BGP is designed to dynamically share routes with peers rather than relying on static routes alone, enabling scalable interdomain routing across the Internet.