Default-Mdt-Based Delivery - HP 6125XLG Ip Multicast Configuration Manual

The public network interface of PE 1 registers the multicast source with the public network RP, and
the public network RP initiates a join to PE 1. A (11.1.1.1, 239.1.1.1) state entry is created on
each device along the path on the public network.
4. At the same time, PE 2 and PE 3 separately 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, or the (*, 239.1.1.1) tree, and the three independent SPTs constitute a
default-MDT.
Default-MDT characteristics
No matter which PIM mode is running on the public network, the default-MDT has the following
characteristics:
• All PE devices that support the same VPN instance join the default-MDT.
All multicast packets of this VPN are forwarded along the default-MDT to every PE device on the
•
public network, even if no active downstream receivers exist.

Default-MDT-based delivery

The default-MDT delivers multicast protocol packets and multicast data packets differently.
Multicast protocol packet delivery
To forward the multicast protocol packets of a VPN over the public network, the local PE device
encapsulates them into public network multicast data packets. These packets are transmitted along the
default-MDT and are then decapsulated on the remote PE device to go into the normal protocol
procedure. Finally a distribution tree is established across the public network.
The following describes how multicast protocol packets are forwarded in different circumstances:
If the VPN network runs PIM-DM or PIM-SSM:
•
Hello packets are forwarded through MTI interfaces to establish PIM neighboring relationships.
A flood-prune process (in PIM-DM) or a join process (in PIM-SSM) is initiated across the public
network to establish an SPT across the public network.
If the VPN network runs PIM-SM:
•
Hello packets are forwarded through MTI interfaces to establish PIM neighboring relationships.
If the receivers and the VPN RP are in different sites, a join process is initiated across the public
network to establish an RPT.
If the multicast source and the VPN RP are in different sites, a registration process is initiated
across the public network to establish an SPT.
NOTE:
PIM mode must be the same for all interfaces that belong to the same VPN, including those interfaces that
are bound with the VPN instance and the MTI interfaces on PE devices.
As shown in
• PIM-SM is running in both the public network and the VPN network.
Receiver for the VPN multicast group G (225.1.1.1) in Site 2 is attached to CE 2.
•
CE 1 of Site 1 acts as the RP for group G (225.1.1.1).
•
The default-group address used to forward public network data is 239.1.1.1.
•
Figure 62:
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