Overview of IGMP

Internet Group Management Protocol (IGMP) has three versions: IGMPv1, IGMPv2, and IGMPv3. All three versions support the Any-Source Multicast (ASM) model, but only IGMPv3 supports the Source-Specific Multicast (SSM) model.

With the wide applications of multicast, increasingly more hosts join multicast groups. Managing multicast groups and members on FWs becomes an important issue.

In the TCP/IP suite, the Internet Group Management Protocol (IGMP) manages IPv4 multicast members. It establishes and maintains the relationship between IP hosts and FWs that are directly connected to the IP hosts.

IGMP is a signaling mechanism of hosts towards FWs on the leaf network of IP multicast. IGMP can be divided into two functional parts: host side and FW side.

The Operating System (OS) of a host determines which version of IGMP is supported by the host.

• All hosts that participate in multicast transmission must be enabled with IGMP. Hosts can randomly join or leave the related multicast groups, and there is no limit on the number of hosts.

• Through IGMP, a multicast FW can know whether there is a member of a certain group in the network segment to which each interface of the FW is connected. Hosts store information only about the multicast groups they join.

At present, IGMP has three versions, that is, IGMPv1 (defined in RFC 1112), IGMPv2 (defined in RFC 2236), and IGMPv3 (defined in RFC 3376). All IGMP versions support the ASM model. IGMPv3 can be directly applied to the SSM model, whereas IGMPv1 and IGMPv2 require the technical support of SSM mapping when they are applied to the SSM model.