1054 BigIron RX Series Configuration Guide53-1001986-01PIM SM traffic snooping41NOTEUse the passive mode of IP multicast traffic reduction instead of the active mode. The passivemode assumes that a router is sending group membership queries as well as join and prunemessages on behalf of receivers. The active mode configures the device to send groupmembership queries.• All the device ports connected to the source and receivers or routers must be in the sameport-based VLAN.• The PIM SM snooping feature assumes that the group source and the device are in differentsubnets and communicate through a router. The source must be in a different IP subnet thanthe receivers. A PIM SM router sends PIM join and prune messages on behalf of a multicastgroup receiver only when the router and the source are in different subnets. When the receiverand source are in the same subnet, they do not need the router in order to find one another.They find one another directly within the subnet.The device forwards all IP multicast traffic by default. Once you enable IP multicast trafficreduction and PIM SM traffic snooping, the device initially blocks all PIM SM traffic instead offorwarding it. The device forwards PIM SM traffic to a receiver only when the device receives ajoin message from the receiver. Consequently, if the source and the downstream router are inthe same subnet, and PIM SM traffic snooping is enabled, the device blocks the PIM SM trafficand never starts forwarding the traffic. This is because the device never receives a joinmessage from the downstream router for the group. The downstream router and group findeach other without a join message because they are in the same subnet.NOTEIf the “route-only” feature is enabled on a BigIron RX, PIM SM traffic snooping will not be supported.NOTEMulticast protocols can only be applied to 1 physical interface. You must create multiple VLANs withboth taggged and untagged ports and ve’s under which you configure pim.Enabling PIM SM traffic snoopingTo enable PIM SM traffic snooping, enter the following commands at the global CONFIG level of theCLI.BigIron RX(config)# ip multicastBigIron RX(config)# ip pimsm-snoopingThe first command enables IP multicast traffic reduction. This feature is similar to PIM SM trafficsnooping but listens only for IGMP information, not PIM SM information. You must enable both IPmulticast traffic reduction and PIM SM traffic snooping to enable the device to listen for PIM SMjoin and prune messages.Syntax: [no] ip multicast [active | passive]This command enables IP multicast traffic reduction. The active | passive parameter specifies themode. The PIM SM traffic snooping feature assumes that the network has routers that are runningPIM SM.Syntax: [no] ip pimsm-snoopingThis command enables PIM SM traffic snooping.
