BGP route weight is a Cisco-specific proprietary attribute used to select the best path when there are multiple routes to the same destination. BGP route weight is local to the router where it is set and is not propagated to other routers. BGP route weight is applied to the routes received from a single neighbor, and the route with the highest weight will be preferred as the best path.
BGP route weight is usually configured using a route map, and it can be assigned to incoming and outgoing routes. When a BGP speaker receives updates from different neighbors, it assigns different weights to the same destination network based on the route maps configured on the router.
If a router receives multiple paths to the same destination network, BGP first determines whether the next hop address is reachable by checking the IGP routing table. If there are multiple paths to the same destination network, BGP assigns a preference to each path, and the path with the highest preference value is selected as the best path.
BGP route weight is a local decision made by each BGP speaker, and it is not shared with other routers. Therefore, it is not suitable for selecting the best path across different autonomous systems. Instead, BGP uses other attributes such as AS path length, multi-exit discriminator (MED), and local preference to select the best path.
