HP MSR2003 Configuration Manual page 189

Figure 62 Transmission of multicast protocol packets
Source
Site 1
S: 192.1.1.1/24
G: 225.1.1.1
Default-group: 239.1.1.1
The multicast protocol packet is delivered as follows:
1. Receiver sends an IGMP report to CE 2 to join the multicast group G. CE 2 creates a local state
entry (*, 225.1.1.1) and sends a join message to the VPN RP (CE 1).
2. After receiving the join message from CE 2, the VPN instance on PE 2 creates a state entry (*,
225.1.1.1) and specifies the MTI interface as the upstream interface. The VPN instance on PE 2
considers the join message to have been sent out of the MTI interface, because step 3 is
transparent to the VPN instance.
3. PE 2 encapsulates the join message into a public network multicast data packet (11.1.2.1,
239.1.1.1) by using the GRE method. In this multicast data packet, the source address is the MD
source interface IP address 11.1.2.1, and the destination address is the default-group address
239.1.1.1. PE 2 then forwards this packet to the public network.
4. The default-MDT forwards the multicast data packet (11.1.2.1, 239.1.1.1) to the public network
instance on all the PE devices. After receiving this packet, every PE device decapsulates it to get the
original join message to be sent to the VPN RP. Then, each PE device examines the VPN RP
address in the join message. If the VPN RP is in the site to which a PE device is connected, the PE
passes the join message to the VPN instance on the PE. Otherwise, the PE discards the join
message.
5. When receiving the join message, the VPN instance on PE 1 considers the received message to be
from the MTI. PE 1 creates a local state entry (*, 225.1.1.1), with the downstream interface being
the MTI and the upstream interface being the one that leads to CE 1. At the same time, the VPN
instance sends a join message to CE 1, which is the VPN RP.
6. After receiving the join message from the VPN instance on PE 1, CE 1 creates a local state entry
(*, 225.1.1.1). If an entry already exists for the group, CE 1 updates the entry.
By now, the construction of an RPT across the public network is completed.
Multicast data packet delivery
After the default-MDT is established, the multicast source forwards the VPN multicast data to the receivers
in each site along the default-MDT. The VPN multicast packets are encapsulated into public network
RP
CE 1
PE 1
BGP: 11.1.1.1/24
BGP: 11.1.3.1/24
PE 3
P
PE 2
MD
BGP: 11.1.2.1/24
Public instance BGP peers
VPN instance join (*, 225.1.1.1)
Public instance join (11.1.2.1, 239.1.1.1)
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Receiver
CE 2
Site 2