BGP uses a set of well-defined rules and criteria to select the best route to a destination network, including:
1. Longer prefix match: BGP will always choose the route with the longest prefix match. For example, if the destination IP address is 10.0.0.0/8, BGP will prefer the route with the longest prefix match of 10.0.0.0/16 over 10.0.0.0/24.
1. Local preference: BGP can use local preference values to influence route selection within an autonomous system (AS). The route with the higher local preference value is preferred.
1. AS path length: BGP prefers the route with the shortest AS path length to the destination network.
1. Multi Exit Discriminator (MED): MED is a metric that indicates the preferred exit point from an AS for a given route. BGP will prefer the route with the lowest MED value.
1. Origin type: BGP prefers routes that originated from within the local AS over routes learned from external peers.
1. Weight: Weight is a Cisco-specific attribute that is used to influence route selection. The route with the highest weight value is preferred.
1. Next hop: BGP prefers routes with a reachable next hop IP address.
If all else is equal, BGP will load-balance over multiple routes.
