This application provides a method and device for sending and obtaining an assert message, to increase packet processing efficiency and reduce overheads of the network device. The method includes: determining, by a network node, a plurality of assert records based on one multicast source address, where each of the plurality of assert records includes the multicast source address and one multicast group address, the plurality of assert records have the same multicast source address, and multicast group addresses included in different assert records in the plurality of assert records are different from each other; generating, by the network node, one assert message based on the plurality of assert records, where the assert message includes the multicast source address and the multicast group addresses in the plurality of assert records; and sending, by the network node, the assert message in a multicast mode.