Application examples of PIM SM traffic snooping
Figure 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.
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 1/4/1, 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.
The following figure shows another example application for PIM SM traffic snooping. This example shows 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 Layer 2 Switches and Layer 3 Switches (routers).
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.