3Com S7906E - Switch, Configuration Manual

Page: 1152 / 2621

1-12
z
For detailed description of RPT-to-SPT switchover, refer to PIM Configuration in the IP Multicast
Volume .
z
The following example explains how multicast data packets are delivered based on the share-MDT
while PIM-DM is running in both the public network and the VPNs network.
As shown in Figure 1-9 , PIM-DM is running in both the public network and the VPNs network, 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 share-group address used to forward public network multicast
data is 239.1.1.1.
Figure 1-9 Delivery of multicast data packets
The private network multicast traffic is delivered across the public network as follows.
1) Source sends customer multicast data (192.1.1.1, 225.1.1.1) to CE 1.
2) CE 1 forwards the private network multicast data along an SPT to CE 1, and the VPN instance on
PE 1 checks the MVRF. If the outgoing interface list of the forwarding entry contains an MTI, PE 1
processes the private network multicast data.. Now, the VPN instance on PE 1 considers that the
private network multicast data has been sent out the MTI.
3) PE 1 encapsulates the multicast data by means of GRE, with its BGP interface address as the
multicast source address and the share-group address as the multicast group address, to convert it
into a normal, public network multicast data packet (11.1.1.1, 239.1.1.1), and then passes the
packet to the public instance on PE 1 to have it forwarded to the public network.
4) The multicast data packet (11.1.1.1, 239.1.1.1) is forwarded to the public instance on all the PE
devices along the share-MDT. Upon receiving this packet, every PE device decapsulates it to turn
it back into a private network multicast data packet, and passes it to the corresponding VPN
instance. If any PE has a downstream interface for an SPT, it forwards the private network
multicast packet down the SPT; otherwise, it discards the packet.