Table of Contents
Advertisement
Figure 68 Multicast data packet delivery
A VPN multicast data packet is delivered across the public network as follows:
Source sends a VPN multicast data packet (192.1.1.1, 225.1.1.1) to CE 1.
1.
CE 1 forwards the VPN multicast data packet along an SPT to PE 1, and the VPN instance on
2.
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 the VPN
multicast data packet to have been sent out of the MTI, because step 3 is transparent to it.
PE 1 encapsulates the VPN multicast data packet into a public network multicast packet
3.
(11.1.1.1, 239.1.1.1) by using the GRE method. The source IP address of the packet is the MD
source interface 11.1.1.1, and the destination address is the default-group address 239.1.1.1.
PE 1 then forwards it to the public network.
The default-MDT forwards the multicast data packet (11.1.1.1, 239.1.1.1) to the public network
4.
instance on all the PE devices. After receiving this packet, every PE device decapsulates it to
get the original VPN multicast data packet, and passes it to the corresponding VPN instance. If
a PE device has a downstream interface for an SPT, it forwards the VPN multicast packet down
the SPT. Otherwise, it discards the packet.
The VPN instance on PE 2 looks up the MVRF and finally delivers the VPN multicast data to
5.
Receiver.
By now, the process of transmitting a VPN multicast data packet across the public network is
completed.
MDT switchover
Switching from default-MDT to data-MDT
When a multicast packet of a VPN is transmitted through the default-MDT on the public network, the
packet is forwarded to all PE devices that support that VPN instance. This occurs whether or not any
active receivers exist in the attached sites. When the rate of the multicast traffic of that VPN is high,
multicast data might get flooded on the public network. This increases the bandwidth use and brings
extra burden on the PE devices.
To optimize multicast transmission of large VPN multicast traffic that enters the public network, the
MD solution introduces a dedicated data-MDT. The data-MDT is built between the PE devices that
190
Advertisement
Table of Contents
Troubleshooting
