3Com Switch 7700, Configuration Manual

Page: 225 / 390

Configuring PIM-SM 217
Configuring PIM-SM is described in the following sections:
■
PIM-SM Operating Principles
■
Preparing to Configure PIM-SM
■
Configuring PIM-SM
PIM-SM Operating
Principles
The PIM-SM working process is as follows: neighbor discovery, building the
RP-rooted shared tree (RPT), multicast source registration and SPT switchover etc.
The neighbor discovery mechanism is the same as that of PIM-DM.
Build the RP shared tree (RPT)
When hosts join a multicast group G, the leaf routers send IGMP messages to
learn the receivers of the multicast group G. The leaf routers calculate the
corresponding rendezvous point (RP) for multicast group G, and then send join
messages to the node of a higher level toward the rendezvous point (RP). Each
router along the path, between the leaf routers and the RP, will generate (*, G)
entries in the forwarding table, indicating that all packets sent to multicast group
G are applicable. When the RP receives packets sent to multicast group G, the
packets will be sent to leaf routers along the path built and then reach the hosts.
In this way, an RP-rooted tree (RPT) is built as shown in the following figure.
Figure 9 RPT Schematic Diagram
Multicast Source S
RPT
join
Multicast source registration
RP
Receiver
RPT
join
Multicast source
registration
Multicast source S
RP
Receiver