Internet Group Management Protocol (IGMP)

is a network protocol that operates at the network layer
is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships
is an integral part of IP multicast

Hosts “join” and “leave” multicast groups using IGMP

Routers create a delivery path through the Internet using routing protocols such as:

PIM (Protocol Independent Multicast)
- Helps build multicast forwarding trees
- Routers maintain multicast states to remember which forwarding trees they are part of
MSDP (Multicast Source Distribution Protocol)