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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 48 Configuring IP Multicast Routing
Configuring IP Multicast Routing
To disable multicasting, use the no ip multicast-routing distributed global configuration command. To
return to the default PIM version, use the no ip pim version interface configuration command. To
disable PIM on an interface, use the no ip pim interface configuration command.
Configuring Source-Specific Multicast
This section describes how to configure source-specific multicast (SSM). For a complete description of
the SSM commands in this section, refer to the “IP Multicast Routing Commands” chapter of the Cisco
IOS IP Command Reference, Volume 3 of 3: Multicast. To locate documentation for other commands that
appear in this chapter, use the command reference master index, or search online.
The SSM feature is an extension of IP multicast in which datagram traffic is forwarded to receivers from
only those multicast sources that the receivers have explicitly joined. For multicast groups configured
for SSM, only SSM distribution trees (no shared trees) are created.

SSM Components Overview

SSM is a datagram delivery model that best supports one-to-many applications, also known as broadcast
applications. SSM is a core networking technology for the Cisco implementation of IP multicast
solutions targeted for audio and video broadcast application environments. The switch supports these
components that support the implementation of SSM:
• Protocol independent multicast source-specific mode (PIM-SSM)
PIM-SSM is the routing protocol that supports the implementation of SSM and is derived from PIM
sparse mode (PIM-SM).
• Internet Group Management Protocol version 3 (IGMPv3)
To run SSM with IGMPv3, SSM must be supported in the Cisco IOS router, the host where the
application is running, and the application itself.

How SSM Differs from Internet Standard Multicast

The current IP multicast infrastructure in the Internet and many enterprise intranets is based on the
PIM-SM protocol and Multicast Source Discovery Protocol (MSDP). These protocols have the
limitations of the Internet Standard Multicast (ISM) service model. For example, with ISM, the network
must maintain knowledge about which hosts in the network are actively sending multicast traffic.
The ISM service consists of the delivery of IP datagrams from any source to a group of receivers called
the multicast host group. The datagram traffic for the multicast host group consists of datagrams with an
arbitrary IP unicast source address S and the multicast group address G as the IP destination address.
Systems receive this traffic by becoming members of the host group.
Membership in a host group simply requires signalling the host group through IGMP version 1, 2, or 3.
In SSM, delivery of datagrams is based on (S, G) channels. In both SSM and ISM, no signalling is
required to become a source. However, in SSM, receivers must subscribe or unsubscribe to (S, G)
channels to receive or not receive traffic from specific sources. In other words, receivers can receive
traffic only from (S, G) channels to which they are subscribed, whereas in ISM, receivers need not know
Step 7 show running-config Verify your entries.
Step 8 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose