Which statement regarding AS_Path is false?

Which statement regarding AS_Path is false?

• A. AS_Path is a list of ASs that a BGP route passes through.
• B. AS_Path is a very important well-known mandatory attribute in BGP.
• C. BGP does not accept routes whose AS_Path attribute contains the local AS number.
• D. When a router has multiple routes to the same destination, it prefers the route with the longer AS_Path attribute.

Answer: (D)

The statement about preferring the route with the longer AS_Path attribute is indeed incorrect. In BGP, the routing decision does not prioritize routes based on the length of the AS_Path attribute. Instead, BGP prefers the route with the shorter AS_Path because a shorter AS_Path usually indicates that the route is more direct and potentially more stable, as it has traversed fewer autonomous systems. The other statements are accurate in describing the AS_Path attribute, its importance in BGP, and the protocol’s behavior concerning the presence of the local AS number. Specifically, the AS_Path serves as a record of the autonomous systems a BGP route has traversed, and it is a well-known mandatory attribute critical to route selection and loop prevention. Furthermore, BGP will indeed reject any route that includes its local AS number in the AS_Path to avoid routing loops. Thus, statement D does not reflect the correct operational principles of BGP regarding AS_Path.

The statement about preferring the route with the longer AS_Path attribute is indeed incorrect. In BGP, the routing decision does not prioritize routes based on the length of the AS_Path attribute. Instead, BGP prefers the route with the shorter AS_Path because a shorter AS_Path usually indicates that the route is more direct and potentially more stable, as it has traversed fewer autonomous systems.

The other statements are accurate in describing the AS_Path attribute, its importance in BGP, and the protocol’s behavior concerning the presence of the local AS number. Specifically, the AS_Path serves as a record of the autonomous systems a BGP route has traversed, and it is a well-known mandatory attribute critical to route selection and loop prevention. Furthermore, BGP will indeed reject any route that includes its local AS number in the AS_Path to avoid routing loops. Thus, statement D does not reflect the correct operational principles of BGP regarding AS_Path.