230
Share-MDT establishment in a PIM-SSM network
Figure 66
Share-MDT establishment in a PIM-SSM network
As shown in
, PIM-SSM is enabled in the network and all the PE devices support VPN instance
A. The process of establishing a share-MDT is as follows:
1.
The public network on PE 1 sends the local BGP MDT routing information, including its BGP
interface address and the share-group address, to PE 2 and PE 3.
2.
PE 2 and PE 3 perform the same operation to exchange their BGP MDT routing information with
one another.
3.
After receiving the BGP MDT information from PE1, PE 2 and PE 3 respectively send a subscribe
message for channel subscription hop-by-hop toward the BGP interface of PE1.
An entry (11.1.1.1, 232.1.1.1) is created on devices on the path toward PE 1 on the public
network. Thus an SPT is created in the network, with PE 1 as its root, PE 2 and PE 3 as its leaves.
4.
At the same time, PE 2 and PE 3 initiate a similar SPT establishment process, respectively.
Finally, three independent SPTs are established in the MD. In the PIM-SS M network, the three
independent SPTs constitute a share-MDT.
NOTE:
In PIM-SSM, subscribe messages are used equivalent to join messages.
Share-MDT characteristics
A share-MDT is characterized as follows, no matter what PIM mode is running on the public network:
•
All PE devices that support this VPN instance join the share-MDT.
•
All VPN multicast packets that belong to this VPN, including protocol packets and data packets, are
forwarded along the share-MDT to every PE device on the public network, even if they have no
active receivers downstream.
Public instance BGP peers
MD
P
PE 3
PE 2
PE 1
BGP: 11.1.2.1/24
BGP: 11.1.1.1/24
SPT (11.1.1.1, 232.1.1.1)
SPT (11.1.2.1, 232.1.1.1)
SPT (11.1.3.1, 232.1.1.1)
BGP: 11.1.3.1/24
Share-Group: 232.1.1.1
