A first network device receives an association relationship sent by a second network device, where the association relationship includes an association relationship between a first path and a second path. The first network device generates first routing information between the first network device and a target network device based on the association relationship, where the first routing information is used by the first network device to send a packet to the target network device through the first path, and when a cross-slice condition is met, the first routing information is used by the first network device to send a packet to the target network device through the second path.