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Networking Fundamentals · Intermediate

Internet Group Management Protocol (IGMP)

The IPv4 protocol hosts use to join and leave multicast groups with their local router (IP protocol 2).

Definition

IGMPv2 adds leave messages and IGMPv3 adds source-specific multicast. Routers send queries and hosts reply with membership reports. Layer 2 switches use IGMP snooping to forward multicast only to ports with interested receivers. IPv6 uses Multicast Listener Discovery (MLD) instead.

Example

A set-top box sends an IGMP join to receive an IPTV channel's multicast group.

Exam tip

IGMP is for IPv4 multicast membership; its IPv6 counterpart is MLD, part of ICMPv6.

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