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Multicast PIM Sparse Mode

A PIM sparse-mode multicast topology with rendezvous point, IGMP joins, and source-tree switchover — foundational multicast design tested in CCNP/CCIE and used in enterprise video/IPTV networks.

The Prompt

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Build a 4-router PIM sparse-mode multicast lab with Cisco IOL. R1, R2, R3, R4 connected in a partial mesh (R1↔R2, R2↔R3, R3↔R4, R1↔R4). Use OSPF as unicast IGP. Enable PIM sparse-mode on all router interfaces. R2 is the Rendezvous Point (RP) with RP address 2.2.2.2 advertised via Auto-RP (or BSR). A multicast source sits off R1 sending to group 239.1.1.1. A multicast receiver sits off R4, joining group 239.1.1.1 via IGMP. Verify the shared tree (RPT) is built from R4 to R2 (RP), the source-tree (SPT) is built from R4 to R1 after SPT switchover threshold, the receiver joins successfully, and traffic flows through the RP initially then switches to the optimal path.

What You'll Build

  • 4 Cisco IOL routers in a partial mesh
  • OSPF unicast underlay
  • PIM sparse-mode everywhere
  • 1 RP (rendezvous point)
  • 1 multicast source + 1 receiver
  • Group 239.1.1.1 traffic flow

Concepts Demonstrated

  • Shared tree (RPT) vs source tree (SPT) — and the SPT switchover threshold
  • RP discovery methods: static, Auto-RP, BSR
  • (*, G) vs (S, G) state
  • IGMP (host-to-router) vs PIM (router-to-router)
  • Why sparse mode replaced dense mode for most deployments

Vendors Used

  • Cisco IOL (all 4 routers)

Difficulty

⭐⭐⭐ Advanced

Variations to Try

  • "Add a second RP with Anycast RP for redundancy"
  • "Replace PIM-SM with PIM Bidirectional (Bidir-PIM) and compare"
  • "Add MSDP between RPs in different ASes for inter-domain multicast"
  • "Test MVPN (multicast VPN) by layering this inside an MPLS L3VPN"

Related Resources

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