4000 Router Series IP Multicast Configuration Guide

incoming interface. The RPF check result determines whether the packet will be forwarded or

discarded. The RPF check mechanism is the basis for most multicast routing protocols to implement

multicast forwarding.

For more information about the RPF mechanism, see "Configuring multicast routing and

forwarding" and "Configuring IPv6 multicast routing and forwarding."

Multicast support for VPNs

Multicast support for VPNs refers to multicast applied in VPNs.

Introduction to VPN instances

VPNs must be isolated from one another and from the public network. As shown in Figure 10, VPN A and

VPN B separately access the public network through PE devices.

Figure 10 VPN networking diagram

• 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.

VPN A

VPN BVPN B

Public network

PE 1

PE 2

PE 3

CE b3

CE a2

CE a3

CE b1

CE a1

CE b2