Users Guide

PIM Sparse-Mode (PIM-SM)

Protocol-independent multicast sparse-mode (PIM-SM) is a multicast protocol that forwards multicast trac to a subnet only after a

request using a PIM Join message.

This behavior is the opposite of PIM-Dense mode, which forwards multicast trac to all subnets until a request to stop.

Topics:

• Implementation Information

• Protocol Overview

• Conguring PIM-SSM

• Enable PIM-SM

• Conguring S,G Expiry Timers

• Conguring a Static Rendezvous Point

• Conguring a Designated Router

• Creating Multicast Boundaries and Domains

• Enabling PIM-SM Graceful Restart

Implementation Information

The Dell Networking implementation of PIM-SM is based on IETF Internet Draft draft-ietf-pim-sm-v2-new-05.

• The maximum number of PIM interfaces is 95.

• The SPT-Threshold is zero, which means that the last-hop designated router (DR) joins the shortest path tree (SPT) to the source after

receiving the rst multicast packet.

• The Dell Networking OS reduces the number of control messages sent between multicast routers by bundling Join and Prune requests

in the same message.

• The system supports PIM-SM on physical, virtual local area network (VLAN), and port-channel interfaces.

• The system supports up to 128 PIM-source-specic multicast (SSM) neighbors/interfaces.

• IPv6 Multicast is not supported on synchronous optical network technologies (SONET) interfaces.

Protocol Overview

PIM-SM initially uses unidirectional shared trees to forward multicast trac; that is, all multicast trac must ow only from the rendezvous

point (RP) to the receivers.

After a receiver receives trac from the RP, PM-SM switches to SPT to forward multicast trac. Every multicast group has an RP and a

unidirectional shared tree (group-specic shared tree).

Requesting Multicast Trac

A host requesting multicast trac for a particular group sends an Internet group management protocol (IGMP) Join message to its

gateway router.

The gateway router is then responsible for joining the shared tree to the RP (RPT) so that the host can receive the requested trac.

710 PIM Sparse-Mode (PIM-SM)