Dell PowerConnect B-RX Configuration Manual page 741

•
NOTE
If the "route-only" feature is enabled on a BigIron RX, PIM SM traffic snooping will not be supported.
Enabling PIM SM traffic snooping
To enable PIM SM traffic snooping, enter the following commands at the global CONFIG level of the
CLI.
BigIron RX(config)# ip multicast
BigIron RX(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.
BigIron RX(config)# no ip pimsm-snooping
If you also want to disable IP multicast traffic reduction, enter the following command.
BigIron RX(config)# no ip multicast
Configuring the PIM SM traffic snooping per VLAN instance
If PIM SM Traffic snooping is not applied globally, you can apply it to individual VLANs instances
within their configurations. In the following example, multicast traffic reduction is applied using PIM
SM Traffic snooping to VLAN 2.
(config)# vlan 2
(config-vlan-2)# multicast pimsm-snooping
BigIron RX Series Configuration Guide
53-1002253-01
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 subnets. 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 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 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.
Configuring IP multicast traffic reduction
23
665