Technical data

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

Receiver

RPT

join

Multicast source

registration

Multicast source S

Receiver