Owner's Manual

730 | Chapter 27. Multicast Routing and Switching
NETGEAR 8800 User Manual
Note: This feature is supported at and above the license level listed for this
feature in the license tables in
Appendix A, XCM8800 Software
Licenses.
PIM Source Specific Multicast (PIM-SSM) is a special case of PIM-SM, in which a host
explicitly sends a request to receive a stream from a specific source, rather than from any
source.
IGMPv3 hosts can use PIM SSM directly, because the ability to request a stream from a
specific source first became available with IGMPv3. The PIM-SSM capable router interprets
the IGMPv3 message to initiate a PIM-SM join towards the source.
Note: IGMPv1 and IGMPv2 hosts can use PIM SSM if IGMP-SSM
mapping is enabled and configured on the XCM8800 switch. For
more information, see Using IGMP-SSM Mapping on page 736.
PIM-SSM has the following advantages:
• No overhead of switching to the source-specific tree and waiting for the first packet to
arrive
• No need to learn and maintain an RP
• Fewer states to maintain on each router
• No need for the complex register mechanism from the source to the RP
• Better security, as each stream is forwarded from sources known in advance
PIM-SSM has the following requirements:
• Any host that participates directly in PIM-SSM must use IGMPv3.
• To support IGMPv1 and IGMPv2 hosts, IGMP-SSM mapping must be enabled and
configured.
PIM-SSM is designed as a subset of PIM-SM and all messages are compliant with PIM-SM.
PIM-SSM and PIM-SM can coexist in a PIM network; only the last hop router need to be
configured for PIM-SSM if both source and receivers are present all the time. However, to
avoid any JOIN delay, it is recommended that you enable all routers along the (s,g) path for
PIM-SSM.
Configuring the PIM-SSM Address Range
A range of multicast addresses is used for PIM-SSM. Within that address range, non-IGMPv3
messages are ignored, and any IGMPv3 exclude messages are ignored. These messages
are ignored for all router interfaces, even those not configured for PIM-SSM. By default there
is no PIM-SSM range specified on the router. If you choose the default keyword in the CLI