IGMP (Internet Group Management Protocol) is a Layer 3 protocol that IPv4 network hosts can use to announce to a router that they want to receive multicast traffic from a specific group.

IGMP currently has three versions whose primary characteristics are:

  • IGMPv1
    • Hosts send membership reports announcing to routers that they want to receive multicast traffic.
    • Routers send membership queries to "ask" if hosts are still interested in receiving traffic.
    • Expiry timers are used to remove hosts from multicast groups.
  • IGMPv2
    • Enhanced version of IGMP
    • Includes mechanisms for hosts to leave a multicast group.
  • IGMPv3
    • Supports source filtering