Which scenario shows the weight attribute is used?

• A. On a router with a single connection to the Internet
• B. When a router teaches the entire AS path to all peers
• C. When a router is multihomed and determines the best path to leave the AS
• D. When all BGP neighbors are EBGP

Answer: (C)

Weight is a locally significant BGP attribute used to influence which path a router will choose for its own outbound traffic. It’s Cisco-specific and is not advertised to peers, so it only affects the router where it’s configured.

In a multihomed network, you have multiple exit points from the AS. By assigning a higher weight to the route learned from the preferred exit, the router will select that path as the best one to use for traffic leaving the AS. This is exactly what the scenario describes: a router that is multihomed determining the best path to leave the AS.

The other scenarios don’t involve choosing an outbound exit point. With a single Internet connection, there’s effectively only one path to use, so weight isn’t needed. Teaching the AS path to all peers pertains to route propagation, not local exit-path selection. Whether neighbors are EBGP doesn’t define the use of weight for deciding the egress path.