Administrative Distance, Access Lists, Route Manipulation, and IP Multicast - CCIE Routing and Switching Exam Certification Guide - page 495

Example 10-18 Configuration of PIM in Dense Mode
ip multicast-routing
!
interface ethernet 0
ip address x
ip pim dense-mode
!
interface ethernet 1
ip address y
ip pim dense-mode
PIM Sparse Mode
PIM-SM is defined in RFC 2362 (experimental). PIM-SM assumes that no hosts want to receive
multicast traffic unless specifically requested. In PIM-SM, a router is selected as the rendezvous
point (RP) . The RP has the task of gathering the information of senders and making the infor-
mation available to receivers. Routers with receivers have to register with the RP. Routers reg-
ister as traffic receivers, not end host systems. The end host systems still request multicast group
membership by using IGMP with their local routers.
Joining PIM-SM
With PIM-SM, designated routers (DR) on end segments receive IGMP query messages from
hosts wanting to join a multicast group (*,G). The router checks to see if it is already receiving
the group for another interface. If it is receiving the group, the new interface is added to the table
and membership reports are sent periodically on the new interface.
If the multicast (*,G) group is not in the multicast table, the interface is added to the multicast
table and the router sends a join message to the RP with multicast address 224.0.0.13 requesting
the multicast group.
Pruning PIM-SM
When a PIM-SM does not have any more multicast receiving hosts or receiving routers out any
of its interfaces, it sends a prune message to the RP. The prune message includes the (*,G) group
to be pruned or removed.
PIM Designated Router
A designated router is selected in multiaccess segments running PIM. The PIM DR is respon-
sible for sending join, prune, and register messages to the RP. The PIM router with the highest
IP address is selected as the DR.