Pim Sparse-Mode (Pim-Sm); Implementation Information; Protocol Overview; Requesting Multicast Traffic - Dell S4820T Configuration Manual

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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.

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-

The platform supports a maximum of 96 PIM interfaces and 2000 multicast entries including (*,G),

and (S,G) entries. There is no limit on the number of PIM neighbors can have.

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

NOTE: Multicast routing is supported across default and non-default VRFs.

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).

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.

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.

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

PIM Sparse-Mode (PIM-SM)