Reference Guide

PIM Sparse-Mode (PIM-SM) | 685
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PIM Sparse-Mode (PIM-SM)
Protocol-independent multicast sparse mode (PIM-SM) is supported on the MXL Switch platform.
PIM-SM is a multicast protocol that forwards multicast traffic to a subnet only upon 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.
Implementation Information
• The Dell Networking implementation of PIM-SM is based on the IETF Internet Draft
draft-ietf-pim-sm-v2-new-05.
• MXL supports a maximum of 31 PIM interfaces and 2K multicast entries including (*,G), and (S,G)
entries. There is no limit on the number of PIM neighbors MXL 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 upon receiving the first multicast packet.
• FTOS reduces the number of control messages sent between multicast routers by bundling Join and
Prune requests in the same message.
• FTOS supports PIM-SM on physical, virtual local area network (VLAN), and port-channel interfaces.
• FTOS supports 2000 IPv6 multicast forwarding entries, with up to 128 PIM-source-specific multicast
(SSM) neighbors/interfaces.
• IPv6 Multicast is not supported on synchronous optical network technology (SONET) 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. Once a receiver receives traffic from the
RP, PIM-SM switches to shortest path trees (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.