Dell PowerConnect B-FCXs Configuration Guide - Page 696

22 PIM SM traffic snooping overview FIGURE 114 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 on 5/1. Forwards multicast data from source on 1/1 to receiver via 5/1 only. Without PIM SM traffic reduction, switch forwards traffic from source out all ports on VLAN. Layer 2 Switch VLAN 2 Port5/1 VLAN 2 Port7/1 VLAN 2 Port1/1 10.10.10.5 Router Source for Groups 239.255.162.1 239.255.162.69 20.20.20.5 Client Router sends a PIM SM join message for 239.255.162.1 10.10.10.6 Router 30.30.30.6 Client Receiver for Group 239.255.162.1 10.10.10.7 Client Client sends an IGMP group membership report for 239.255.162.69 Receiver for Group 239.255.162.69 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 PowerConnect B-Series FCX Configuration Guide 53-1002266-01