3com S7906E Installation Instruction

 

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per-VPN-instance basis, while the public network multicast traffic between the PE devices and the 

P devices is transmitted through the public instance.  

2)  Logically, an MD defines the transmission range of the multicast traffic of a specific VPN over the 

public network; physically, an MD identifies all the PE devices that support that VPN in the public 

network. Different VPN instances correspond to different MDs. As shown in 

area in the center of each VPN instance plane represents an MD, which serves that particular VPN. 

All the private network multicast traffic in that VPN is transmitted within that MD.  

3)  Inside an MD, all the private traffic is transmitted through the MT. The process of multicast traffic 

transmission through an MT is as follows: the local PE device encapsulates the private network 

data into a public network packet, which is then forwarded in the public network, and the remote PE 

device decapsulates the packet to turn it back into a private packet.  

4)  The local PE device sends out private network data through the MTI, and the remote PE devices 

receive the private data through the MTI. As shown in 

, an MD can be thought of as a 

private data transmission pool, and an MTI can be thought of an entrance/exit of the pool. The local 

PE device puts the private data into the transmission pool (the MD) through the entrance (MTI), 

and the transmission pool automatically duplicates the private data and transmits the data to each 

exit (MTI) of the transmission pool, so that any remote PE device that needs the data can get it from 

the respective exit (MTI).  

Figure 1-3 Relationship between PIM in the public instance and an MD in a VPN instance 

 

 

5)  Each VPN instance is assigned a unique share-group address. The private network data is 

transparent to the public network. A PE device encapsulates any private network multicast packet 

within a normal public network multicast packet, no matter what multicast group the private network 

packet is destined for and whether it is a protocol packet or a data packet, and uses the 

share-group as the public network multicast group for the packet. Then, the PE sends the public 

network multicast packet onto the public network.  

6)  A share-group corresponds to a unique MD; for each share-group, a unique share-MDT is 

constructed by leveraging the public network resources for multicast data forwarding. All the 

private network multicast packets transmitted in this VPN are forwarded along this share-MDT, no 

matter at which PE device they entered the public network.