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the share-MDT, and then de-encapsulated 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 the following circumstances:
1.
If the VPN network runs PIM-DM or PIM-SSM:
{
Hello packets are forwarded among 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.
2.
If the VPN network runs PIM-SM:
{
Hello packets are forwarded among 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.
3.
If the VPN network runs BIDIR-PIM:
{
Hello packets are forwarded among 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 the receiver-side RPT.
{
If the multicast source and the VPN RP are in different sites, multicast data is transmitted
across the public network to establish the source-side RPT.
IMPORTANT:
All interfaces that belong to the same VPN, including those interfaces with VPN instance bindings
and the MTI on PE devices, must run the same PIM mode.
The following example explains how multicast protocol packets are delivered based on the
share-MDT when PIM-SM is running in both the public network and the VPN network, with receivers
and the VPN RP located in different sites.
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, and CE 1 of Site 1 acts as the
RP for group G 225.1.1.1; the share-group address used to forward public network data is 239.1.1.1.
