A method for determining a route leak, applied to a network monitoring device, wherein the network monitoring device manages a first autonomous system (AS 100), and the method comprises: receiving an extended border gateway protocol monitoring protocol BMP packet sent by a first border node of the first autonomous system (AS 100) and an extended BMP packet sent by a second border node of the first autonomous system (AS 100); determining, based on the extended BMP packet sent by the first border node and the extended BMP packet sent by the second border node of the first autonomous system (AS 100), a receiving relationship of a route prefix that has been received by the first border node from a second autonomous system (AS 11), and a sending relationship of the route prefix that has been sent by the second border node to a third autonomous system (AS 22), wherein the receiving relationship is a client-to-provider relationship, a peer-to-peer relationship, or a provider-to-client relationship, and the sending relationship is the client-to-provider relationship, the peer-to-peer relationship, or the provider-to-client relationship; and determining, based on the receiving relationship and the sending relationship, whether the route prefix is leaked, wherein the receiving an extended BMP packet sent by a first border node of the first autonomous system (AS 100) and an extended BMP packet sent by a second border node of the first autonomous system (AS 100) comprises: receiving a first extended BMP route monitoring packet sent by the first border node, wherein the first extended BMP route monitoring packet carries the receiving relationship; and receiving a second extended BMP route monitoring packet sent by the second border node, wherein the second extended BMP route monitoring packet carries the sending relationship; and the determining a receiving relationship and a sending relationship based on the extended BMP packet sent by the first border node and the extended BMP packet sent by the second border node of the first autonomous system (AS 100) comprises: determining the receiving relationship and the sending relationship based on the receiving relationship carried in the first extended BMP route monitoring packet and the sending relationship carried in the second extended BMP route monitoring packet. receiving an extended border gateway protocol monitoring protocol BMP packet sent by a first border node of the first autonomous system (AS 100) and an extended BMP packet sent by a second border node of the first autonomous system (AS 100); determining, based on the extended BMP packet sent by the first border node and the extended BMP packet sent by the second border node of the first autonomous system (AS 100), a receiving relationship of a route prefix that has been received by the first border node from a second autonomous system (AS 11), and a sending relationship of the route prefix that has been sent by the second border node to a third autonomous system (AS 22), wherein the receiving relationship is a client-to-provider relationship, a peer-to-peer relationship, or a provider-to-client relationship, and the sending relationship is the client-to-provider relationship, the peer-to-peer relationship, or the provider-to-client relationship; and determining, based on the receiving relationship and the sending relationship, whether the route prefix is leaked, wherein the receiving an extended BMP packet sent by a first border node of the first autonomous system (AS 100) and an extended BMP packet sent by a second border node of the first autonomous system (AS 100) comprises: receiving a first extended BMP route monitoring packet sent by the first border node, wherein the first extended BMP route monitoring packet carries the receiving relationship; and receiving a second extended BMP route monitoring packet sent by the second border node, wherein the second extended BMP route monitoring packet carries the sending relationship; and the determining a receiving relationship and a sending relationship based on the extended BMP packet sent by the first border node and the extended BMP packet sent by the second border node of the first autonomous system (AS 100) comprises: determining the receiving relationship and the sending relationship based on the receiving relationship carried in the first extended BMP route monitoring packet and the sending relationship carried in the second extended BMP route monitoring packet. receiving a first extended BMP route monitoring packet sent by the first border node, wherein the first extended BMP route monitoring packet carries the receiving relationship; and receiving a second extended BMP route monitoring packet sent by the second border node, wherein the second extended BMP route monitoring packet carries the sending relationship; and the determining a receiving relationship and a sending relationship based on the extended BMP packet sent by the first border node and the extended BMP packet sent by the second border node of the first autonomous system (AS 100) comprises: determining the receiving relationship and the sending relationship based on the receiving relationship carried in the first extended BMP route monitoring packet and the sending relationship carried in the second extended BMP route monitoring packet.