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Routing & Switching · Intermediate

PIM Sparse Mode (PIM-SM)

A pull-model multicast protocol where routers explicitly join a shared tree rooted at a rendezvous point and may switch to a source tree.

Definition

Receivers' last-hop routers send (*,G) joins toward the RP. The source's first-hop router registers with the RP via unicast Register messages, and the RP joins toward the source. Last-hop routers then typically switch to the shortest path tree (S,G) after the first packet.

Example

ip pim sparse-mode ; ip pim rp-address 10.0.0.1

Exam tip

Every router must know the RP address for PIM-SM to work; RP discovery is static, Auto-RP or BSR.

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