H3C Technologies H3C S12500 Series Switches - Manual (Page 267)

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NOTE:
For a given VPN instance, the share-MDT and the switch-MDT are both forwarding tunnels in the same
MD. A share-MDT is uniquely identified by a share-group address, and a switch-MDT is uniquely
identified by a switch-group address. Each share-group is uniquely associated with a set of switch-group
addresses (a switch-group-pool).
Backward switching from switch-MDT to share-MDT
After the VPN multicast traffic is switched to the switch-MDT, the multicast traffic conditions might change
and no longer meet the aforesaid switchover criterion. In this case, PE 1, as in the preceding example,
initiates a backward MDT switchover process. When any of the following criteria is met, the multicast
traffic is switched from the switch-MDT back to the share-MDT:
• The associated switch-group-pool is changed and the switch-group address for encapsulating the
VPN multicast data is out of the new address pool.
• The ACL rule for controlling the switching of VPN multicast traffic from the share-MDT to the
switch-MDT is changed and the VPN multicast data fails to pass the new ACL rule.
Multi-AS MD VPN
If nodes of a VPN network are allocated in multiple autonomous systems (ASs), these VPN nodes must be
interconnected. To implement multi-AS VPN, VRF-to-VRF PE interconnectivity and multi-hop EBGP
interconnectivity are available.
VRF-to-VRF PE interconnectivity
As shown in Figure 74 , a VPN involves AS 1 and AS 2. PE 3 and PE 4 are the autonomous system
boundary router (ASBR) for AS 1 and AS 2 respectively. PE 3 and PE 4 are interconnected through their
respective VPN instance and treat each other as a CE device.
Figure 74 VPN instance-VPN instance interconnectivity
By using this method, a separate MD must be established within each AS, and VPN multicast traffic
between different ASs is transmitted between these MDs.
IMPORTANT:
Because only VPN multicast traffic is forwarded between ASBRs, different PIM modes can run within
different ASs. However, the same PIM mode (PIM-DM, PIM-SM, BIDIR-PIM, or PIM-SSM) must run on all
interfaces that belong to the same VPN (including interfaces with VPN bindings on ASBRs).