Pim-Sm (Protocol Independent Multicast — Sparse Mode) - Fujitsu PSWITCH 2048T User Manual

User's Guide
The multicast messages contain the source and group information so that
downstream routers can build up their multicast forwarding tables. If the source
goes inactive, the tree is torn down. Multicast messages arriving at a router over
the proper receiving interface (that is, the interface that provides the shortest path
back to the source) are forwarded on all downstream interfaces until unnecessary
branches of the tree are explicitly pruned. In addition to the prune messages,
PIM-DM uses graft messages and assert messages. Graft messages are used when
a new host wants to join a group, and assert messages are used to shut off
duplicate flows.
To minimize the repeated flooding of datagrams and the subsequent pruning
associated with a particular (S, G) pair, PIM-DM uses a State Refresh message. This
message is sent by the router(s) directly connected to the Source and is propagated
throughout the network. When received by a router on its RPF interface, the State
Refresh message causes an existing prune state to be refreshed. These State
Refresh messages are generated periodically by the router directly attached to the
Source.
Routing must be enabled on the switch and the applicable interfaces before
PIM-DM becomes enabled and operational. The switch supports PIM-DM Version 2.
The PIM-DM feature supports distributing both IPv4 and IPv6 routes.
3.1.3.9. PIM-SM (Protocol Independent Multicast — Sparse Mode)
As with PIM-DM, PIM-SM is not dependent on any particular unicast routing
protocols to construct the forwarding information it uses for multicast packets,
although unicast information is needed for actual forwarding. The Sparse Mode
(SM) version of PIM is most appropriate for networks with relatively limited
bandwidth and where group membership is widely distributed across regions.
Sparse mode protocols begin with the assumption that few routers in the network
is involved in any given multicast path. Sparse mode routers minimize network
traffic by adding branches to the tree only when explicitly requested to do so.
Therefore, sparse mode protocols such as PIM-SM are better suited to WANs than
are dense mode protocols.
PIM-SM uses the following concepts:
 Rendezvous Point (RP):
The root of a shared distribution tree down which all multicast traffic flows.
 Designated Router (DR):
Responsible for sending join messages to the RP for group members and for
December/2018
FUJITSU PSWITCH
95