Multi-Instance Pim - 3Com MSR 50 Series Configuration Manual

1172 C 71: PIM C
HAPTER ONFIGURATION
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Multi-Instance PIM

Construction of SPT
Whether to build an RPT for PIM-SM or an SPT for PIM-SSM depends on whether
the multicast group the receiver is to join falls in the SSM group address range
(SSM group address range reserved by IANA is 232.0.0.0/8).
Figure 348 SPT establishment in PIM-SSM
Source
Server
SPT
Subscribe message
Multicast packets
As shown in Figure 348, Host B and Host C are multicast information receivers.
They send IGMPv3 report messages denoted as (Include S, G) to the respective DRs
to express their interest in the information of the specific multicast source S. If they
need information from other sources than S, they send an (Exclude S, G) report.
No matter what the description is, the position of multicast source S is explicitly
specified for receivers.
The DR that has received the report first checks whether the group address in this
message falls in the SSM group address range:
If so, the DR sends a subscribe message for channel subscription hop by hop
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toward the multicast source S. An (Include S, G) or (Exclude S, G) entry is
created on all routers on the path from the DR to the source. Thus, an SPT is
built in the network, with the source S as its root and receivers as its leaves.
This SPT is the transmission channel in PIM-SSM.
If not, the PIM-SM process is followed: the DR needs to send a (*, G) join
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message to the RP, and a multicast source registration process is needed.
In PIM-SSM, the "channel" concept is used to refer to a multicast group, and the
"channel subscription" concept is used to refer to a join message.
A multicast router running multiple instances maintains an independent set of PIM
neighbor table, multicast routing table, BSR information and RP-set information
for each instance. To the outside, the router appears to be a group of multicast
routers, each running PIM independently from the others.
Upon receiving a multicast protocol packet, the multicast router determines the
VPN instance this protocol packet belongs to and passes the packet to PIM
RP
Host A
Receiver
DR
Host B
DR
Receiver
Host C