Many services, including video conference, whiteboard and video broadcasting, have been running over LANs. However, most of LANs, such as Ethernet, treat multicast just as broadcast, and they all have few supports for multicast. In this paper, a multicast protocol in an LAN switch, named IGMP snooping, is implemented based on VLAN and IGMP. IGMP snooping will be applied to the IP multicast stream control on the switch Ethernet. The basic idea, syntax and semantics of this protocol are given in this paper, and the verification and test procedure is also provided.