PIM-SM Operation
Designated Router (DR)
Neighboring PIM-SM routers multicast periodic “Hello” messages
to each other - default 30 secs.
Hello-interval tunable for faster convergence
On receipt of a Hello message
 a router stores the IP address and priority for that neighbor
Router with highest IP address is selected as the DR, if the
priorities match
When DR goes down:
new one selected by scanning all neighbors on the interface and choosing
the one with the highest IP address
DR sends
“Join/Prune” messages toward the RP from receiver network
“Register” messages toward the RP from source network