When is the weight attribute used?

• A. When a router runs in single-homed mode
• B. When a router is multihomed and determines the best path to leave the AS
• C. During initial neighbor establishment only
• D. When using MED to influence external path selection

Answer: (B)

Weight is a Cisco-specific BGP path attribute that the local router uses to influence its own best-path decision. It’s the top criterion in the BGP decision process on that router, and it is not advertised to other routers. In a multihomed setup, where a router has multiple possible exit points out of the AS, weight lets you steer which path should be considered the preferred one for sending traffic. By assigning a higher weight to routes learned from a preferred provider, the router installs that route in its routing table and uses that exit point for outbound traffic. This helps control outbound routing locally without affecting other routers’ views.

It doesn’t come into play during initial neighbor establishment, it isn’t used to influence MED, and in a single-homed situation there are typically no competing exit paths to steer, so weight isn’t needed.