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Foundry Configuration Guide for the FESX, FSX, and FWSX
18 - 8
© Foundry Networks, Inc.
December 2005
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The PIM SM snooping feature assumes that the group source and the device are in different sub-nets and
communicate through a router. The source must be in a different IP sub-net than the receivers. A PIM SM
router sends PIM join and prune messages on behalf of a multicast group receiver only when the router and
the source are in different sub-nets. When the receiver and source are in the same sub-net, they do not need
the router in order to find one another. They find one another directly within the sub-net.
The device forwards all IP multicast traffic by default. Once you enable IP multicast traffic reduction and PIM
SM traffic snooping, the device initially blocks all PIM SM traffic instead of forwarding it. The device forwards
PIM SM traffic to a receiver only when the device receives a join message from the receiver. Consequently, if
the source and the downstream router are in the same sub-net, and PIM SM traffic snooping is enabled, the
device blocks the PIM SM traffic and never starts forwarding the traffic. This is because the device never
receives a join message from the downstream router for the group. The downstream router and group find
each other without a join message because they are in the same sub-net.
NOTE:
If the “route-only” feature is enabled on a Layer 3 Switch, PINM SM traffic snooping will not be supported.
Enabling PIM SM Traffic Snooping
To enable PIM SM traffic snooping, you must enable IP multicast traffic reduction, then enable snooping. To
enable PIM SM traffic snooping, enter the following commands at the global CONFIG level of the CLI:
FESX424 Switch(config)# ip multicast
FESX424 Switch(config)# ip pimsm-snooping
The first command enables IP multicast traffic reduction. This feature is similar to PIM SM traffic snooping but
listens only for IGMP information, not PIM SM information. You must enable both IP multicast traffic reduction and
PIM SM traffic snooping to enable the device to listen for PIM SM join and prune messages.
Syntax:
[no] ip multicast [active | passive]
This command enables IP multicast traffic reduction. The
active | passive
parameter specifies the mode. The
PIM SM traffic snooping feature assumes that the network has routers that are running PIM SM.
Syntax:
[no] ip pimsm-snooping
This command enables PIM SM traffic snooping.
To disable the feature, enter the following command:
FESX424 Switch(config)# no ip pimsm-snooping
If you also want to disable IP multicast traffic reduction, enter the following command:
FESX424 Switch(config)# no ip multicast
Displaying IP Multicast Information
The following sections show how to display and clear IP multicast reduction information.
Displaying Multicast Information on Layer 2 Switches
To display IP multicast information on Layer 2 Switches, including the state of the traffic reduction and traffic
snooping features, use the following CLI methods.
Summary of Contents for FastIron Edge Switch X424
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