11
•
To ensure multicast packet transmission on the network, different routing tables are used to
guide multicast forwarding. These routing tables include unicast routing tables, routing tables
for multicast (for example, the MBGP routing table), and static multicast routing tables.
•
To process the same multicast information from different peers received on different interfaces,
the multicast device performs an RPF check on each multicast packet. 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
Multicast support for VPNs
Multicast support for VPNs refers to multicast applied in VPNs.
Introduction to VPN instances
VPNs are isolated from one another and from the public network. As shown in
, 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 A
VPN A
VPN B
VPN B
Public network
P
PE 1
PE 2
PE 3
CE b3
CE a2
CE a3
CE b1
CE a1
CE b2
