A packet sending method includes obtaining, by a client device, an Internet Protocol (IP) anycast address of the anycast server cluster and an IP unicast address of the target server, generating, by the client device, an IP detection packet, where the IP detection packet is used to detect whether the target server is reachable based on the IP anycast address, and the IP detection packet includes the IP anycast address and the IP unicast address of the target server, and instructs the target server to replace the IP unicast address of the target server with the IP anycast address, and sending, by the client device, the IP detection packet to the target server.