Multi-As Md Vpn - HP A6600 Configuration Manual

before it enters the public network. Then, the multicast stream is switched from the share-MDT to the
switch-MDT, to deliver the multicast data to only those receivers that need it.
The process of share-MDT to switch-MDT switchover is as follows:
The source-side PE (PE 1 in this example) device periodically checks the forwarding rate of the VPN
1.
multicast traffic. Share-MDT to switch-MDT switchover takes place only when the following criteria
are both met:
The VPN multicast data has passed the filtering by an ACL rule for share-MDT to switch-MDT
•
switchover, and
The traffic rate of the VPN multicast stream has exceeded the switchover threshold and stayed higher
•
than the threshold for a certain length of time.
PE 1 chooses an idle switch-group address from the switch-group-pool and sends an MDT switchover
2.
message to all the other PE devices down the share-MDT. This message contains the VPN multicast
source address, the VPN multicast group address and the switch-group address.
Each PE device that receives this message checks whether it interfaces with a VPN that has receivers
3.
of that VPN multicast stream. If so, it joins the switch-MDT rooted at PE 1. Otherwise, it caches the
message and will join the switch-MDT when it has attached receivers.
After sending the MDT switchover message, PE 1 waits a certain length of time and then starts using
4.
the switch-group address to encapsulate the VPN multicast data, so that the multicast data is
forwarded down the switch-MDT.
After the multicast traffic is switched from the share-MDT to the switch-MDT, PE 1 continues sending
5.
MDT switchover messages periodically, so that subsequent PE devices with attached receivers can
join the switch-MDT. When a downstream PE device has no longer active receivers attached to it, it
leaves the switch-MDT.
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, namely, 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 traffic rate of the VPN multicast data has fallen under the switchover threshold and stayed lower
•
than the threshold for a certain length of time (namely, the switch-holddown period).
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 ASs, these VPN nodes must be interconnected. To
implement multi-AS VPN, VRF-to-VRF PE interconnectivity and multi-hop EBGP interconnectivity are
available.
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