IGMP (Internet Group Management Protocol): This is a host-router signaling protocol. Its primary function is to manage group membership on the last-hop subnet (the segment connecting the router to the hosts). Hosts use it to join groups, and routers use it to query for members.

PIM (Protocol Independent Multicast): This is a Layer 3 routing protocol used between routers. It builds distribution trees (Shortest Path Trees or Shared Trees) to route multicast traffic across the network infrastructure from the source to the receiver's last-hop router.

IGMP Snooping: This is a Layer 2 optimization mechanism running on switches. Without it, switches broadcast multicast traffic to all ports (flooding). IGMP Snooping "snoops" on IGMP messages to build a forwarding table, ensuring traffic is only forwarded to ports with interested receivers, thus suppressing flooding.

IETF RFC 2236, Internet Group Management Protocol, Version 2, Section 1 "Introduction". (Defines IGMP's role in allowing hosts to report group memberships to immediate neighbor routers).

https://doi.org/10.17487/RFC2236

IETF RFC 7761, Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised), Section 1 "Introduction". (Describes PIM's role in building distribution trees to forward multicast packets based on routing information).

https://doi.org/10.17487/RFC7761

IETF RFC 4541, Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches, Section 1 "Introduction". (Explains how snooping switches limit the flooding of multicast traffic on Layer 2).

https://doi.org/10.17487/RFC4541

Cisco Systems, IP Multicast Technology Overview, "Multicast Basics". (Confirming the functional distinction between IGMP for member management, PIM for routing, and Snooping for L2 constraint).

Document ID: 29232