Objectives
The simulator ticks each one as soon as the network meets it.
On SW1, SW2 and SW3 run ip multicast admin-state enable (IGMP for the whole switch).
Run ip load pim, then add every IP interface: ip pim interface "name".
Enable ip pim dense admin-state enable.
Join 239.1.1.1 on PC3, then ping 239.1.1.1 from SRC: PC3 replies.
On SW3, show ip pim sgroute lists 10.1.1.10/239.1.1.1 with flag D.
Before you start
Like OSPF, PIM must be loaded (ip load pim) before any other ip pim command. Dense mode floods the stream and prunes branches without receivers; no RP is used.
Concept
PIM dense mode: flood and prune
Dense mode assumes every network wants the stream. The first packets flood out of every PIM interface that passes the RPF check, and routers with no receivers downstream send a Prune back, so the flood shrinks to the branches that need it. The flood repeats every three minutes.
Concept
IGMP: how a receiver asks for a group
A multicast group (224.0.0.0/4) is an address many receivers can listen to at once. A host tells its local router it wants a group with an IGMP membership report; the router then pulls the stream toward that LAN. IGMPv2 can only name the group; IGMPv3 can also name the source.
