Brocade TurboIron 24X Series Configuration Guide - Manual (Page 805)

Brocade TurboIron 24X Series Configuration Guide 771
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PIM SM traffic snooping overview
PIM SM traffic snooping overview
When multiple PIM sparse routers connect through a snooping-enabled device, the device always
forwards multicast traffic to these routers. For example, PIM sparse routers R1, R2 and R3 connect
through a device. Assume R2 needs traffic, and R1 sends it to the device, which forwards it to both
R2 and R3, even though R3 does not need it. A PIM SM snooping-enabled device listens to join and
prune messages exchanged by PIM sparse routers, and stops traffic to the router that sends prune
messages. This allows the device to forward the data stream to R2 only.
PIM SM traffic snooping requires IGMP snooping to be enabled on the device. IGMP snooping
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.
PIM SM snooping support
Table 115 shows PIM SM snooping version support on the devices.
Application examples
Figure 103 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.
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. Since 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 1, since 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 result,
the device does not see a join message on behalf of the client. However, since IGMP snooping 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 IGMP snooping 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.
TABLE 115 PIM SM snooping support
Version support Supported in software code...
PIM SM V2 snooping L2, L3