H3C Technologies H3C S12500 Series Switches - Manual (Page 260)

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along the path on the public network. This forms an SPT with PE 1 as the root, and PE 2 and PE 3 as
leaves.
At the same time, PE 2 and PE 3 respectively initiate a similar flood-prune process. Finally, three
independent SPTs are established in the MD. In the PIM-DM network, these independent SPTs constitute
a share-MDT.
Share-MDT establishment in a PIM-SM network
Figure 69 Share-MDT establishment in a PIM-SM network
As shown in Figure 69 , PIM-SM 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 initiates a join to the public network RP, with the share-group address
as the multicast group address in the join message, and a (*, 239.1.1.1) state entry is created on
each device along the path on the public network. At the same time, PE 2 and PE 3 respectively
initiate a similar join process. Finally, an RPT is established in the MD, with the public network RP
as the root and PE 1, PE 2 and PE 3 as leaves.
2. The public network on PE 1 registers the multicast source with the public network RP and the public
network RP initiates a join to PE 1. With the BGP interface address as the multicast source address
and the share-group address as the multicast group address, a (11.1.1.1, 239.1.1.1) state entry
is created on each device along the path on the public network. At the same time, PE 2 and PE 3
respectively initiate a similar register process. Finally, three SPTs between the PE devices and the
RP are established in the MD.
In the PIM-SM network, the RPT, the (*, 239.1.1.1) tree, and the three independent SPTs constitute a
share-MDT.
Public instance BGP peers
RPT (*, 239.1.1.1)
MD
P
RP
PE 3
PE 2 PE 1
BGP: 11.1.2.1/24 BGP: 11.1.1.1/24
SPT (11.1.1.1, 239.1.1.1)
SPT (11.1.2.1, 239.1.1.1)
SPT (11.1.3.1, 239.1.1.1)
BGP: 11.1.3.1/24
Share-Group: 239.1.1.1