Enabling Forwarding of IGMP Protocol Packets to the Backup PW

On a network shown in Figure 1, PE3 is dual-homed to PE1 and PE2 across a virtual private line service (VPLS) network, and set up master and backup pseudo wires (PWs) with them to enhance link reliability. The PW to PE1 is the master PW, and that to PE2 is the backup one.

If PE3 is not configured to send IGMP Report messages to the backup PW, Report messages sent in response to the IGMP Query messages from CE1 will not be sent upstream over the backup PW. If the link or PE1 on the master PW fails, PE2 cannot resume multicast data forwarding immediately because it has no matching Layer 2 multicast forwarding entries. As a result, services will be interrupted for a relatively long time.

To enable fast failover of multicast traffic to the backup link or PE, configure PE3 to forward IGMP Report messages to the backup PW. In this way, PE2 on the backup PW can create Layer 2 multicast forwarding entries. Once the backup PW changes to the master state, multicast data traffic can be forwarded over this PW immediately to ensure normal multicast services.

After this function is enabled, PE3 can receive two copies of identical multicast data when the link and PE on the master PW are working normally. PE3, however, does not forward the multicast data received from the backup PW to the receiver. Therefore, this function does not affect multicast services on the network.

In Figure 1, if the positions of the source and receiver are swapped, you need to configure PE3 to forward IGMP Query messages to the backup PW.

Figure 1 Before and after a PE is configured to forward IGMP Report messages to the backup PW