API Guide

● RFC 4601 for PIM-SM
● RFC 3569 for PIM-SSM
PIM-SM
PIM sparse mode (PIM-SM) is a multicast routing protocol for networks with receivers that are sparsely distributed. Receivers
have to explicitly send a join message to join particular groups or sources. PIM join and prune messages are used to join and
leave multicast distribution trees.
PIM-SM uses shared trees with the root node being the rendezvous point (RP). All multicast sources use the RP to route the
traffic to the receiver. The last hop router (LHR) sends an (*,G) join message towards the RP. The designated router
connected to the first hop router (FHR) encapsulates multicast data that comes from the multicast source in PIM control
messages and sends it via unicast to the RP as PIM register messages. The RP sends an (S, G) join towards the source. When
the RP receives native data traffic from the source, it sends a register stop message to the FHR.
OS10 supports static and dynamic configuration of an RP address for a multicast group.
To keep the PIM-SM state alive, all PIM neighbors send periodic hello messages.
You must enable PIM-SM on each of the participating interfaces. Be sure to have multicast routing enabled on the system. To
do this, use the ip multicast-routing command from CONFIGURATION mode.
OS10# configure terminal
OS10(config)# interface vlan 100
OS10(conf-if-vl-100)# ip pim sparse-mode
PIM-SSM
PIM-SSM uses source-based trees. A separate multicast distribution tree is built for each multicast source that sends data to a
multicast group. Each multicast distribution tree has as its root node a router near the source. Sources send data directly to the
root of the tree. PIM-SSM enables receivers to specify the source from which to receive data and the multicast group they
want to join. The receiver identifies a multicast data stream using the source and group address pair (S, G) instead of the group
address alone (*, G).
NOTE:
● PIM-SSM requires receivers to support IGMP version 3.
● The default PIM-SSM range is 232.0.0.0/8. The default range is always supported and the range can never be smaller
than the default.
● If the PIM-SSM group range overlaps with the multicast group range that the candidate RP advertises, the router
chooses the RP learned from the BSR and creates (*, G) entries instead of (S, G) entries.
Advantages of PIM-SSM
Advantages of PIM-SSM include the following:
● PIM-SSM forwards multicast traffic from a single source to a subnet. Other versions of PIM requires the receiver to
subscribe to a group. The receiver receives traffic not just from the source that it is interested in, but from all the sources
that send to that group. PIM-SSM requires the receiver to specify the sources in which they are interested in to avoid
receiving unnecessary traffic.
● PIM-SSM is more efficient than PIM-SM because it immediately creates shortest path trees (SPT) to the source rather than
using shared trees. PIM-SM requires a shared tree rooted at the RP because IGMPv2 receivers do not express the source
information in their membership reports. Multicast traffic passes from the source to the receiver through the RP, until the
last hop router (LHR) learns the source address, at which point it switches to the SPT.
PIM-SSM uses IGMPv3. Because receivers subscribe to a source and group, the RP and shared tree are unnecessary; only
SPTs are used. On OS10 systems, it is possible to use PIM-SM with IGMPv3 to achieve the same result, but PIM-SSM
eliminates the unnecessary protocol overhead.
Multicast
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