BGP route selection
BGP discards routes with unreachable NEXT_HOPs. If multiple routes to the same destination are available, BGP selects the optimal route in the following sequence:
The route with the highest Preferred_value.
The route with the highest LOCAL_PREF.
The route generated by the network command, the route redistributed by the import-route command, or the summary route in turn.
The route with the shortest AS_PATH.
The IGP, EGP, or INCOMPLETE route in turn.
The route with the lowest MED value.
The route learned from EBGP, confederation EBGP, confederation IBGP, or IBGP in turn.
The route with the smallest IGP metric.
The route with the smallest recursion depth.
If all routes are received from EBGP peers and the peers have different router IDs, the route that used to be an optimal route becomes the optimal route.
The route advertised by the router with the smallest router ID.
If one of the routes is advertised by a route reflector, BGP compares the ORIGINATOR_ID of the route with the router IDs of other routers. Then, BGP selects the route with the smallest ID as the optimal route.
The route with the shortest CLUSTER_LIST.
The route advertised by the peer with the lowest IP address.
The CLUSTER_IDs of route reflectors form a CLUSTER_LIST. If a route reflector receives a route that contains its own CLUSTER ID in the CLUSTER_LIST, the router discards the route to avoid routing loops.
If load balancing is configured, the system selects available routes to implement load balancing.