Overview of IGMP

Definition

In the TCP/IP protocol suite, the Internet Group Management Protocol (IGMP) manages IPv4 multicast members, and sets up and maintains multicast member relationships between IP hosts and their directly connected multicast routers.

After IGMP is configured on hosts and their directly connected multicast routers, the hosts can dynamically join multicast groups, and the multicast routers can manage multicast group members on the local network.

IGMP is a signaling mechanism used by IP multicast on the end network. IGMP is applicable to both the host side and router side:

On the host side, IGMP allows hosts to dynamically join and leave multicast groups anytime and anywhere.

A host's operating system (OS) determines the IGMP version that the host supports.
On the router side, IGMP enables a router to determine whether multicast receivers of a specific group exist. Each host stores information about only the multicast groups it joins.

IGMP has three versions, as listed in Table 1:

**Table 1** IGMP versions
IGMP Version	Model Supported
IGMPv1	Any-source multicast (ASM) and source-specific multicast (SSM) To support SSM in IGMPv1, the SSM mapping technique is required.
IGMPv2	ASM and SSM To support SSM in IGMPv2, the SSM mapping technique is required.
IGMPv3	ASM and SSM

Purpose

IGMP allows receivers to access IP multicast networks, join multicast groups, and receive multicast data from multicast sources. IGMP manages multicast group members by exchanging IGMP messages between hosts and routers. IGMP records host join and leave information on interfaces, ensuring correct multicast data forwarding on the interfaces.