Dell PowerConnect B-RX Configuration Manual page 1129

Notice that the receiver for group 239.255.162.69 is directly connected to the device. As result,
the device does not see a join message on behalf of the client. However, since IP multicast traffic
reduction also is enabled, the device uses the IGMP group membership report from the client to
select the port for forwarding traffic to group 239.255.162.69 receivers.
The IP multicast traffic reduction feature and the PIM SM traffic snooping feature together build a
list of groups and forwarding ports for the VLAN. The list includes PIM SM groups learned through
join messages as well as MAC addresses learned through IGMP group membership reports. In this
case, even though the device never sees a join message for the receiver for group
239.255.162.69, the device nonetheless learns about the receiver and forwards group traffic to
the receiver.
The device stops forwarding IP multicast traffic on a port for a group if the port receives a prune
message for the group.
Notice that the ports connected to the source and the receivers are all in the same port-based
VLAN on the device. This is required for the PIM SM snooping feature. The feature also requires the
source and the downstream router to be on different IP subnets, as shown in
Figure 137
devices on the edge of a Global Ethernet cloud (a Layer 2 Packet over SONET cloud). Assume that
each device is attached to numerous other devices such as other BigIron RX.
FIGURE 137
The devices on the edge of the Global Ethernet cloud are configured for IP multicast traffic
reduction and PIM SM traffic snooping. Although this application uses multiple devices, the
feature has the same requirements and works the same way as it does on a single device.
BigIron RX Series Configuration Guide
53-1001810-01
shows another example application for PIM SM traffic snooping. This example shows
PIM SM traffic reduction in global Ethernet environment
The switches "snoop" for PIM SM
join and prune messages.
Switch A detects a source on port1/1
and a receiver for that source's group
on port5/1. The switch forwards
multicast data from the source on port1/1
out port5/1 only, which has the receiver.
Without PIM SM traffic snooping, the
switch would forward traffic from the
source out all other ports.
VLAN 2
Port1/1
Switch B
VLAN 2
Port5/1
Router sends a
PIM SM join message
Router
for 239.255.162.1.
Client
Receiver for Group
239.255.162.1
PIM SM traffic snooping
VLAN 2
Switch A
Port1/1
Router
10.10.10.5
VLAN 2
VLAN 2
Port5/1
Port7/1
VLAN 2
Port1/1
Switch C
VLAN 2
Port5/1
Client sends an
IGMP group
Client
membership report
for 239.255.162.69.
Receiver for Group
239.255.162.69
41
Figure 136.
Source for Groups
239.255.162.1
239.255.162.69
20.20.20.5
Client
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