Configuring IP Multicast Traffic Reduction
December 2005
© Foundry Networks, Inc.
18 - 5
PIM SM Traffic Snooping
By default, when a Foundry device receives an IP multicast packet, the device does not examine the multicast
information in the packet. Instead, the device simply forwards the packet out all ports except the port that received
the packet. In some networks, this method can cause unnecessary traffic overhead in the network. For example,
if the Foundry device is attached to only one group source and two group receivers, but has devices attached to
every port, the device forwards group traffic out all ports in the same broadcast domain except the port attached to
the source, even though there are only two receivers for the group.
PIM SM traffic snooping eliminates the superfluous traffic by configuring the device to forward IP multicast group
traffic only on the ports that are attached to receivers for the group.
PIM SM traffic snooping requires IP multicast traffic reduction to be enabled on the device. IP multicast traffic
reduction configures the device to listen for IGMP messages. PIM SM traffic snooping provides a finer level of
multicast traffic control by configuring the device to listen specifically for PIM SM join and prune messages sent
from one PIM SM router to another through the device.
Configuration Notes
•
This feature applies only to PIM SM version 2 (PIM V2).
•
This feature is supported in the Layer 2 switch code only.
•
This feature is supported in software release 02.2.00 and later for the FESX and FWSX.
•
This feature is supported in software release 02.3.01 and later for the FSX.
Application Examples
Figure 18.1 shows an example application of the PIM SM traffic snooping feature. In this example, a device is
connected through an IP router to a PIM SM group source that is sending traffic for two PIM SM groups. The
device also is connected to a receiver for each of the groups.
Figure 18.1
PIM SM traffic reduction in enterprise network
Client
Client
The Layer 2 switch snoops for
PIM SM join and prune messages.
The switch detects a source on port 1/1
and a receiver for that source’s group
on port 5/1. The switch forwards
multicast data from the source on port 1/1
out port 5/1 only, which has the receiver.
Without PIM SM traffic reduction, the
switch would forward traffic from the
source out all other ports in the VLAN.
Receiver for Group
239.255.162.69
VLAN 2
Port 7/1
Source for Groups
239.255.162.1
239.255.162.69
Receiver for Group
239.255.162.1
Client
30.30.30.6
Client sends an
IGMP group
membership report
for 239.255.162.69.
Router
Router
VLAN 2
Port 1/1
10.10.10.5
10.10.10.7
10.10.10.6
VLAN 2
Port 5/1
Router sends a
PIM SM join message
for 239.255.162.1.
20.20.20.5
Layer 2 Switch
Содержание FastIron Edge Switch X424
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