A first network device in a first device group receives a first packet that is sent by a first terminal device connected to the first network device and whose destination address is an IP address of a second terminal device connected to a second network device in a second device group. When a first inter-group interconnection link exists between the first network device and the second device group, and congestion does not occur on the first inter-group interconnection link, the first network device sends the first packet to the second network device through the first inter-group interconnection link.