Abstract: The realization techniques of multicast based on data link level (DLL) are discussed, considering the application program interface (API)--packet socket, a low level communication interface provided by Linux system. The features and types of packet socket are analyzed. The programming methods and steps of multicast by using packet socket are expatiated and the related system calls and analyses of the program are presented. It is proved to be effective for multicast on DLL. This conclusion is valuable for network monitors and some special application areas.