Objectives
The simulator ticks each one as soon as the network meets it.
R1 (Cisco): ip multicast-routing, ip pim sparse-mode on G0/0, G0/1 and Loopback0, ip pim rp-address 1.1.1.1.
R2 (Huawei): multicast routing-enable, pim sm on both interfaces, static-rp 1.1.1.1 in the pim view.
R3 (Arista): pim ipv4 sparse-mode on both interfaces, router multicast → ipv4 → routing, rp address 1.1.1.1.
Join 239.1.1.1 on PC3, then ping 239.1.1.1 from SRC: PC3 replies.
Before you start
PIM is standard across vendors, only the commands differ. Every router must agree on the RP, and the RPF check follows each router’s OSPF route back to the source and the RP.
Concept
PIM sparse mode (ASM): shared tree, register, SPT
Sparse mode sends a stream only where it is requested. Receivers’ routers join a shared tree rooted at a rendezvous point (RP); the source’s router registers the stream to the RP; once the stream arrives, the receiver’s router joins the source directly on the shortest-path tree (SPT).
Concept
The RPF check: multicast follows unicast routes backwards
A router accepts a multicast packet only on the interface it would use to reach the packet’s source (reverse path forwarding), and sends joins out of that same interface toward the RP or source. The unicast routing table decides the path, so a missing route or a link without PIM breaks multicast even when ping works.
