A system and method for packet processing, the method being applied to a first network device and including sending a first packet to a second network device, where a control packet header of the first packet includes a first number, and the first number indicates a number of a packet that carries the first number and that is between the first network device and the second network device, and receiving a first acknowledgement packet from the second network device, where the first acknowledgement packet comprises an indication indicating whether the second network device receives the first packet.