IGMPv2

IGMPv2 is the second version of the Internet Group Management Protocol, used in IPv4 networks to manage host membership in multicast groups on local networks. It enables routers to learn which hosts are interested in receiving multicast traffic and to prune data forwarding when no members remain. IGMPv2 was defined in RFC 2236 and published in 1997 as an improvement over IGMPv1.

Key features introduced in IGMPv2 include Leave Group messages, which allow a host to announce that it will no longer receive a specific multicast group, and the use of Group-Specific and General Queries by routers to actively determine group membership. Hosts respond to queries with Membership Reports, and a Max Response Time field controls how quickly responses must be sent. Reports are suppression-enabled to reduce traffic on the link.

Operation: A router periodically transmits General Queries on a link to discover active multicast groups. Hosts that are members of any groups respond with Membership Reports. When a host leaves a group, it may send a Leave Group message to prompt immediate pruning of the multicast stream if no other members remain on the segment; routers may then halt forwarding for that group on that link.

Compatibility and usage: IGMPv2 maintains backward compatibility with IGMPv1, allowing mixed deployments. It remains widely used in IPv4 multicast environments. IGMPv2 does not introduce Source-Specific Multicast; that capability was extended in later revisions (IGMPv3). For IPv6, the equivalent functionality is provided by Multicast Listener Discovery (MLD).