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• The P device belongs to the public network. The CE devices belong to their respective VPNs. Each
CE device serves its own VPN and maintains only one set of forwarding mechanisms.
• The PE devices connect to the public network and the VPNs. Each PE device must strictly distinguish
the information for different networks, and maintain a separate forwarding mechanism for each
network. On a PE device, a set of software and hardware that serve the same network forms an
instance. Multiple instances can exist on the same PE device, and an instance can reside on
different PE devices. On a PE device, the instance for the public network is called the public network
instance, and those for VPNs are called VPN instances.
Multicast application in VPNs
A PE device that supports multicast for VPNs does the following operations:
• Maintains an independent set of multicast forwarding mechanisms for each VPN, including the
multicast protocols, PIM neighbor information, and multicast routing table. In a VPN, the device
forwards multicast data based on the forwarding table or routing table for that VPN.
• Implements the isolation between different VPNs.
• Implements information exchange and data conversion between the public network and VPN
instances.
For example, as shown in Figure 9, a mu
lticast source in VPN A sends multicast data to a multicast group.
Only receivers that belong to both the multicast group and VPN A can receive the multicast data. The
multicast data is multicast both in VPN A and on the public network.
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