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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 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.
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.
• 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 after receiving the first multicast packet.
• The Dell Networking operating system (OS) reduces the number of control messages sent between
multicast routers by bundling Join and Prune requests in the same message.
• The Dell Networking OS supports PIM-SM on physical, virtual local area network (VLAN), and port-
channel interfaces.
• The Dell Networking OS 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 technologies (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.
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.
PIM Sparse-Mode (PIM-SM)
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