R0106-HP MSR Router Series IP Multicast Configuration Guide(V7)

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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 that belong to 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 tha
t
are bound with the VPN instance and the MTI interfaces on PE devices.
As shown in Figure 62:
• PIM-SM is running in both the public network and the VPN network.
• R e c e i v e r f o r t h e V P N m u l t i c a s t g r o u p G ( 2 2 5 .1.1.1) i n S i t e 2 i s a t t a c h e d t o C E 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.