Overview

PIM snooping runs on Layer 2 devices. It works with IGMP snooping to analyze received PIM messages, and adds the ports that are interested in specific multicast data to a PIM snooping routing entry. In this way, the multicast data can be forwarded to only the ports that are interested in the data.

As shown in Figure 20, Source 1 sends multicast data to multicast group G1, and Source 2 sends multicast data to multicast group G2. Receiver 1 belongs to G1, and Receiver 2 belongs to G2. The Layer 2 switch's interfaces that connect to the PIM routers are in the same VLAN.

• When the Layer 2 switch runs only IGMP snooping, it performs the following actions:

  1. Maintains the router ports according to the received PIM hello messages that PIM routers send.

  2. Floods all other types of received PIM messages except PIM hello messages in the VLAN.

  3. Forwards all multicast data to all router ports in the VLAN.

  Each PIM router in the VLAN, whether interested in the multicast data or not, can receive all multicast data and all PIM messages except PIM hello messages.

• When the Layer 2 switch runs both IGMP snooping and PIM snooping, it performs the following actions:

  1. Examines whether a PIM router is interested in the multicast data addressed to a multicast group according to the received PIM messages that the router sends.

  2. Adds only the ports that connect to the router and are interested in the data to a PIM snooping routing entry.

  3. Forwards PIM messages and multicast data to only the routers that are interested in the data, which saves network bandwidth.

For more information about IGMP snooping and router ports, see "Configuring IGMP snooping."

PIM snooping can run in PIM-SM and PIM-SSM networks. Do not configure PIM snooping in PIM-DM or BIDIR-PIM networks. For more information about PIM, see "Configuring PIM."