NOTE
Use the passive mode of IGMP snooping instead of the active mode. The passive mode assumes that
a router is sending group membership queries as well as join and prune messages on behalf of
receivers. The active mode configures the device to send group membership queries.
• All the device ports connected to the source and receivers or routers must be in the same port-
based VLAN.
• The PIM SM snooping feature assumes that the group source and the device are in different
subnets and communicate through a router. The source must be in a different IP subnet 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 subnet. When the receiver and
source are in the same subnet, they do not need the router in order to find one another. They find
one another directly within the subnet.
The device forwards all IP multicast traffic by default. Once you enable IGMP snooping 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 subnet, 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
subnet.
NOTE
If the "route-only" feature is enabled on a Layer 3 Switch, PIM SM traffic snooping will not be
supported.
PIM SM snooping configuration
Configuring PIM SM snooping on a Brocade device consists of the following global and VLAN-specific
tasks.
Perform the following global PIM SM snooping task:
• Enabling or disabling PIM SM snooping
Perform the following VLAN-specific PIM SM snooping tasks:
• Enabling PIM SM snooping on a VLAN
• Disabling PIM SM snooping on a VLAN

Enabling or disabling PIM SM snooping

Use PIM SM snooping only in topologies where multiple PIM sparse routers connect through a device.
PIM SM snooping does not work on a PIM dense mode router which does not send join messages and
traffic to PIM dense ports is stopped. A PIM SM snooping-enabled device displays a warning if it
receives PIM dense join or prune messages.
To enable PIM sparse snooping globally, enter the ip pimsm-snooping command.
device(config)#ip pimsm-snooping

PIM SM snooping configuration

38 FastIron Ethernet Switch IP Multicast Configuration Guide
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