Dell PowerConnect B-FCXs Configuration Manual page 696

22
PIM SM traffic snooping overview
FIGURE 114
NOTE
IP address 239.192.0.0/14 must be used for IPv4 Organization Local Scope.
When PIM SM traffic snooping is enabled, the device starts listening for PIM SM join and prune
messages and IGMP group membership reports. Until the device receives a PIM SM join message
or an IGMP group membership report, the device forwards IP multicast traffic out all ports. Once
the device receives a join message or group membership report for a group, the device forwards
subsequent traffic for that group only on the ports from which the join messages or IGMP reports
were received.
In this example, the router connected to the receiver for group 239.255.162.1 sends a join
message toward the group source. Because PIM SM traffic snooping is enabled on the device, the
device examines the join message to learn the group ID, then makes a forwarding entry for the
group ID and the port connected to the receiver router. The next time the device receives traffic for
239.255.162.1 from the group source, the device forwards the traffic only on port 5/1, because
that is the only port connected to a receiver for the group.
Notice that the receiver for group 239.255.162.69 is directly connected to the device. As a 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.
654
PIM SM traffic reduction in an enterprise network
Switch snoops for PIM SM
join and prune messages.
Detects source on port1/1
and receiver for source group
Layer 2 Switch
on 5/1. Forwards multicast
data from source on 1/1 to
VLAN 2
receiver via 5/1 only.
Port5/1
Without PIM SM traffic reduction,
switch forwards traffic from source
out all ports on VLAN.
10.10.10.6
Router sends a PIM SM
join message for
Router
239.255.162.1
30.30.30.6
Client
Receiver for Group
239.255.162.1
VLAN 2
Port1/1
Router
10.10.10.5
VLAN 2
Port7/1
10.10.10.7
Client sends an
IGMP group
membership report for
Client
239.255.162.69
Receiver for Group
239.255.162.69
PowerConnect B-Series FCX Configuration Guide
Source for Groups
239.255.162.1
239.255.162.69
20.20.20.5
Client
53-1002266-01