One sender, many receivers, and a forwarding model that runs backwards. Articles tagged Multicast cover IGMP, PIM sparse and dense mode, RP placement and the RPF check.
Multicast fails silently, and nearly every ticket collapses into three signatures: a silent receiver, an RPF failure, or a missing RP. Captured on CML with IOS XE 17.18.2: healthy PIM sparse mode state before and after the source goes active, how to read every field of show ip mroute, and each...
Standard PIM sparse mode scales beautifully for a handful of sources and thousands of receivers. Push it the other direction,
Everything hard about PIM sparse mode traces back to one assumption: receivers do not know who the sources are. Drop
Unicast routing looks forward: where is this packet going? Multicast routing looks backward: did this packet arrive from the right
PIM sparse mode is where multicast stops being theory and becomes state machines. It is the protocol that turns "
IGMP is the only part of multicast a host ever speaks. Before PIM builds a single tree, before an RP
Every multicast design decision starts with an address. Which range you pick determines whether routers forward the traffic at all,
Send one packet, deliver it to a hundred receivers, and put exactly one copy on each link along the way.