Connectivity Guide

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 configuration of an RP address for a multicast group.
To keep the PIM-SM state alive, all PIM join messages are periodically re-transmitted.
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 adjacent to the source. Sources send data directly
to the root of the tree. PIM-SSM allows receivers to specify the source from which to receive data as well as 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.
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.
Configure PIM-SSM
To configure a group range for PIM-SSM:
NOTE: The IP range, 232.0.0.0/8 is reserved for SSM. You do not have to explicitly configure this range.
1. Create an ACL rule to specify the range of addresses that should use SSM.
OS10# configure terminal
OS10(config)# ip access-list ssm-1
OS10(config-ipv4-acl)# permit ip any 236.0.0.0/8
OS10(config-ipv4-acl)# exit
618
Multicast