A method includes: establishing, by a first network device, a first BMP session with a second network device, and establishing a second BMP session with a third network device; receiving a first BGP route set sent by the second network device, where the first BGP route set includes a BGP route sent by the second network device to the third network device; receiving a second BGP route set sent by the third network device, where the second BGP route set includes the BGP route received by the third network device from the second network device; and when detecting that the second BGP route set includes a first BGP route but the first BGP route set does not include the first BGP route, determining the first BGP route as an unavailable route.