IGMPv3

IGMPv3 is the third version of the Internet Group Management Protocol, used in IPv4 networks to manage membership of hosts in multicast groups. It operates between hosts and their local multicast routers to determine which devices should receive traffic addressed to a given multicast group and to support more selective delivery.

A principal feature of IGMPv3 is source-specific multicast (SSM). Receivers can specify which source addresses they want to receive for a given group, enabling tighter control over multicast data. In a membership report, a host advertises the sources from which it wishes to receive traffic and the mode that applies to those sources.

IGMPv3 reports carry one or more group records, each with a record type and a list of source addresses. The six possible record types are MODE_IS_INCLUDE, MODE_IS_EXCLUDE, CHANGE_TO_INCLUDE_MODE, CHANGE_TO_EXCLUDE_MODE, ALLOW_NEW_SOURCES, and BLOCK_OLD_SOURCES. These types define how the receiver’s interest in particular sources for a group should be applied by routers.

Query types in IGMPv3 include General Query, Group-Specific Query, and Group-and-Source Query. Routers issue these queries to solicit current membership state, and hosts respond with Membership Reports that reflect the desired sources and mode for each group.

Deployment and compatibility notes indicate that IGMPv3 is defined in RFC 3376. It is not fully backwards compatible with older versions, though many devices implement dual-version support to enable interoperability. IGMPv3 supports broader multicast control and is often used in conjunction with PIM routing protocols.