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Routing & Switching · Foundational

IP Multicast

One-to-many or many-to-many delivery where a source sends a single stream to a group address and routers replicate it only where receivers exist.

Definition

IPv4 multicast uses class D addresses 224.0.0.0/4 and relies on IGMP for host membership and PIM for routing between routers. Forwarding is based on reverse path forwarding to avoid loops. Uses include IPTV, market data, video distribution and VXLAN BUM transport.

Example

A video server streams to 239.1.1.1 and only subnets with joined receivers get the traffic.

Exam tip

Multicast saves bandwidth versus unicast replication; sources need not join the group.

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