A network device, comprising: a switch chip and a Central Processing Unit, CPU , wherein the switch chip at least comprises a CPU interface (101_1), and the CPU at least comprises a media access controller (102_1) and a Buffer (102_2); and wherein the network device further comprises a conversion apparatus , wherein the conversion apparatus has means configured to: receive a first packet uploaded by the switch chip to the CPU through the CPU interface (101_1), wherein, the conversion apparatus is characterised in that it is further configured to: obtain a second packet by migrating a private information header from an Ethernet header of the first packet to a specified position of the first packet, calculate a Cyclic Redundancy Check, CRC, code of the second packet, obtain a third packet by replacing a CRC code already carried in the second packet with the calculated CRC code, and send the third packet to the Buffer (102_2) on the CPU for buffering, wherein the specified position is a position other than the Ethernet header in the first packet, and the private information header indicates information related to packet characteristics added by the switch chip according to a private protocol. a switch chip and a Central Processing Unit, CPU , wherein the switch chip at least comprises a CPU interface (101_1), and the CPU at least comprises a media access controller (102_1) and a Buffer (102_2); and wherein the network device further comprises a conversion apparatus , wherein the conversion apparatus has means configured to: receive a first packet uploaded by the switch chip to the CPU through the CPU interface (101_1), wherein, the conversion apparatus is characterised in that it is further configured to: obtain a second packet by migrating a private information header from an Ethernet header of the first packet to a specified position of the first packet, calculate a Cyclic Redundancy Check, CRC, code of the second packet, obtain a third packet by replacing a CRC code already carried in the second packet with the calculated CRC code, and send the third packet to the Buffer (102_2) on the CPU for buffering, wherein the specified position is a position other than the Ethernet header in the first packet, and the private information header indicates information related to packet characteristics added by the switch chip according to a private protocol. receive a first packet uploaded by the switch chip to the CPU through the CPU interface (101_1), wherein, the conversion apparatus is characterised in that it is further configured to: obtain a second packet by migrating a private information header from an Ethernet header of the first packet to a specified position of the first packet, calculate a Cyclic Redundancy Check, CRC, code of the second packet, obtain a third packet by replacing a CRC code already carried in the second packet with the calculated CRC code, and send the third packet to the Buffer (102_2) on the CPU for buffering, wherein the specified position is a position other than the Ethernet header in the first packet, and the private information header indicates information related to packet characteristics added by the switch chip according to a private protocol. obtain a second packet by migrating a private information header from an Ethernet header of the first packet to a specified position of the first packet, calculate a Cyclic Redundancy Check, CRC, code of the second packet, obtain a third packet by replacing a CRC code already carried in the second packet with the calculated CRC code, and send the third packet to the Buffer (102_2) on the CPU for buffering, wherein the specified position is a position other than the Ethernet header in the first packet, and the private information header indicates information related to packet characteristics added by the switch chip according to a private protocol. <EOS>