Configuration Guide User guide

FastIron Configuration Guide 1465
53-1002494-02
PIM SM traffic snooping overview
PIM SM traffic snooping overview
When multiple PIM sparse routers connect through a snooping-enabled device, the Brocade 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.
Application examples of PIM SM traffic snooping
Figure 170 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. 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, because 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.
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 devices on the edge of
the Global Ethernet cloud are configured for IGMP snooping 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.