Users Guide

PIM Sparse-Mode (PIM-SM)

PIM-sparse mode (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

• Configuring S,G Expiry Timers

• Configuring a Static Rendezvous Point

• Configuring a Designated Router

• Creating Multicast Boundaries and Domains

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 S5000 supports a maximum of 96 PIM interfaces and 2K multicast entries including (*,G), and (S,G)

entries. There is no limit on the number of PIM neighbors the S5000 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

interfaces.

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).

PIM Sparse-Mode (PIM-SM) 802