Administrator Guide

Table Of Contents
PIM Sparse-Mode (PIM-SM)
Protocol-independent multicast sparse-mode (PIM-SM) is supported on Dell Networking OS.
PIM-SM is a multicast protocol that forwards multicast traffic to a subnet only after a request using a PIM Join message; this
behavior is the opposite of PIM-Dense mode, which forwards multicast traffic to all subnets until a request to stop.
Topics:
Implementation Information
Protocol Overview
Configuring PIM-SM
Enable PIM-SM
Configuring S,G Expiry Timers
Configuring a Static Rendezvous Point
Configuring a Designated Router
Creating Multicast Boundaries and Domains
Enabling PIM-SM Graceful Restart
Implementation Information
Be aware of the following PIM-SM implementation information.
The Dell Networking implementation of PIM-SM is based on IETF Internet Draft draft-ietf-pim-sm-v2-new-05.
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 first multicast packet.
Dell Networking OS reduces the number of control messages sent between multicast routers by bundling Join and Prune
requests in the same message.
Dell Networking OS supports PIM-SM on physical, virtual local area network (VLAN), and port-channel interfaces.
NOTE: Multicast routing is supported across default and non-default VRFs.
Protocol Overview
PIM-SM initially uses unidirectional shared trees to forward multicast traffic; that is, all multicast traffic must flow only from the
rendezvous point (RP) to the receivers.
After a receiver receives traffic from the RP, PM-SM switches to SPT to forward multicast traffic. Every multicast group has an
RP and a unidirectional shared tree (group-specific shared tree).
Requesting Multicast Traffic
A host requesting multicast traffic 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
traffic.
1. After receiving an IGMP Join message, the receiver gateway router (last-hop DR) creates a (*,G) entry in its multicast
routing table for the requested group. The interface on which the join message was received becomes the outgoing interface
associated with the (*,G) entry.
2. The last-hop DR sends a PIM Join message to the RP. All routers along the way, including the RP, create an (*,G) entry
in their multicast routing table, and the interface on which the message was received becomes the outgoing interface
associated with the (*,G) entry. This process constructs an RPT branch to the RP.
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