4000 Router Series IP Multicast Configuration Guide

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VPN multicast data packets are forwarded across the public network differently in the following

circumstances:

1. If PIM-DM or PIM-SSM is running in the VPN, the multicast source forwards multicast data packets

to the receivers along the VPN SPT across the public network.

2. When PIM-SM is running in the VPN:

{ Before the RPT-to-SPT switchover, if the multicast source and the VPN RP are in different sites, the

multicast source forwards VPN multicast data packets to the VPN RP along the VPN SPT across

the public network. If the VPN RP and the receivers are in different sites, the VPN RP forwards

VPN multicast data packets to the receivers along the VPN RPT over the public network.

{ After the RPT-to-SPT switchover, if the multicast source and the receivers are in different sites, the

multicast source forwards VPN multicast data packets to the receivers along the VPN SPT across

the public network.

For more information about RPT-to-SPT switchover, see "Configuring PIM."

The following example explains how multicast data packets are delivered based on the default-MDT

when PIM-DM is running in both the public network and the VPN network.

As shown in Figure 63,

PIM-DM is running in both the public network and the VPN sites, Receiver of the

VPN multicast group G (225.1.1.1) in Site 2 is attached to CE 2, and Source in Site 1 sends multicast data

to multicast group (G). The default-group address used to forward public network multicast data is

23 9.1.1.1.

Figure 63 Multicast data packet delivery

A VPN multicast data packet is delivered across the public network as follows:

3. Source sends a VPN multicast data packet (192.1.1.1, 225.1.1.1) to CE 1.

4. CE 1 forwards the VPN multicast data packet along an SPT to PE 1, and the VPN instance on PE

1 examines the MVRF.

If the outgoing interface list of the forwarding entry contains an MTI, PE 1 processes the VPN

multicast data packet as described in step 3. The VPN instance on PE 1 considers that the VPN

multicast data packet has been sent out of the MTI because step 3 is transparent to it.