Overview IGMP

IGMP (Internet Group Management Protocol) is the protocol for managing the IP multicast members in the TCP/IP protocol stack, used to set up and maintain the multicast group member relation between the IP host and the direct neighboring multicast device.

IGMP has three versions. Currently, the widely-used is IGMPv2. IGMPv2 has three kinds of packets: query packets, group member relation report and group member leave packet.

Query packet includes the general query packet and the specified group query packet. The device gets to know which members there are in the direct-connected network via the general query packets and whether there are the members of one specified group in the direct-connected network via the specified group query packets.

Group member relation report: When the host wants to add into one multicast group, the host immediately sends the group member relation report to the desired multicast group. When the host receives one query packet, it also sends the group member relation report.

Group member leave packet: When the host leaves one multicast group, send one group member leave report. When the device receives the group member leave packet, send the specified group query to confirm whether one specified group has members.