A method, including obtaining a first protocol descriptor according to a protocol header field of an input packet, and further according to a preset protocol field mapping relationship, where the first protocol descriptor corresponds to the protocol header field of the input packet, and where the preset protocol field mapping relationship comprises a mapping relationship between the first protocol descriptor and the protocol field of the input packet, obtaining a second protocol descriptor according to the first protocol descriptor, obtaining, according to the preset protocol field mapping relationship and the second protocol descriptor, a second protocol header field, and obtaining an output packet, where the output packet comprises the second protocol header field.