A communication method implemented by a first network device, the method includes receiving, by the first network device, a first packet. The first packet may include a first segment identifier (SID) and a second SID. Determining, by the first network device whether the first SID is unavailable. If the first SID is unavailable, the first network device obtains the second SID based on the first SID, and updates a destination address in the first packet with the second SID, to generate a second packet.