3com S7906E 설치 설명서

 

1-11 

The work process of multicast protocol packets is as follows:  

1)  Receiver sends an IGMP membership report for multicast group G to CE 2. CE 2 creates a local (*, 

225.1.1.1) state entry and sends a join message to the VPN RP (CE 1).  

2)  Upon receiving the join message from CE 2, the VPN instance on PE 2 creates a (*, 225.1.1.1) 

state entry with the upstream interface being the MTI, and then PE 2 processes the join message. 

Now, the VPN instance on PE 2 considers that the join message has been sent out the MTI.  

3)  PE 2 encapsulates the join message by means of Generic Routing Encapsulation (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 (11.1.2.1, 

239.1.1.1), and then passes the packet to the public instance on PE 2 to have it forwarded to the 

public network.  

4)  The multicast data packet (11.1.2.1, 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 join message to be sent to the VPN RP. Then, each PE device checks the join 

message. If any PE device finds that the VPN RP is in the site it interfaces with, it passes the join 

message to the VPN instance on it; otherwise, it discards the join message.  

5)  When receiving the join message, the VPN instance on PE 1 considers that it received the 

message from the MTI. PE 1 creates a local (*, 225.1.1.1) state entry, with the downstream 

interface being the MTI and the upstream interface being the one that leads to CE 1. At the same 

time, it sends a join message to CE 1, which is the VPN RP.  

6)  Upon receiving the join message from the VPN instance on PE 1, CE 1 creates a local (*, 225.1.1.1) 

state entry or updates the entry if it already exists. By now, the construction of an RPT across the 

public network is completed.  

 

For details about GRE, refer to GRE Configuration in the VPN Volume.  

 

After the share-MDT is established, the private network multicast data flows to the receivers in each site 

along the distribution tree. The private network multicast packets are encapsulated into normal public 

network multicast packets on the local PE device, transmitted along the share-MDT, and then 

decapsulated on the remote PE device and transmitted in the private network.  

1)  If PIM-DM or PIM-SSM is running in the VPNs network, the customer multicast traffic flows along 

the SPTs across the public network.  

2)  On a VPNs network running PIM-SM (before RPT-to-SPT switchover only):  

z 

If the receivers and the VPN RP are in different sites, the customer multicast traffic flows along the 

RPT across the public network.  

z 

If the multicast source and the VPN RP are in different sites, the customer multicast traffic flows 

along the SPTs across the public network.