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Operation Manual – Multicast

H3C S3600 Series Ethernet Switches-Release 1510 Chapter 7 PIM Configuration

7-5

In order that the receiver can receive the multicast data streams of the specific IGMP

group, PIM-SM adopts rendezvous points (RP) to forward multicast information to all

PIM-SM routers with receivers. RP is adopted in multicast forwarding. As a result, the

network bandwidth that the data packets and control packets occupy is reduced, and

the processing overhead of the router is also reduced.

At the receiving end, the router connected to the information receiver sends Join

messages to the RP corresponding to the multicast group. The Join message reaches

the root (namely, RP) after passing each router. The passed paths become the

branches of the rendezvous point tree (RPT).

If the sending end wants to send data to a multicast group, the first hop router will send

registration information to RP. When the registration information reaches RP, the

source tree establishment is triggered. Then, the multicast source sends the data to RP.

When the data reaches RP, the multicast packets are replicated and sent to the

receiver along the RPT. Replication happens only where the tree branches. The

procedure is repeated automatically until the multicast packets reach the receiver.

PIM-SM does not reply on any specific unicast routing protocol. Instead, it performs

RPF check based on the existing unicast routing table.

7.1.4 Work Mechanism of PIM-SM

The working procedure of PIM-SM is:

z Neighbor discovery

z DR election

z RP discovery

z RPT shared tree building

z Multicast source registration

z Switching RPT to SPT

I. Neighbor discovery

The neighbor discovery mechanism is the same as described in PIM-DM. It is also

implemented through Hello messages sent between each router.

II. DR election

With the help of Hello messages, DR can be elected for the shared network, such as

Ethernet. DR will be the unique multicast information forwarder in the network. In either

the network connected to the multicast source S or the network connected to the

receiver, DR must be elected as long as the network is a shared network. The DR at the

receiving end sends Join messages to RP and the DR at the multicast source side

sends Register messages to RP, as shown in

Figure 7-3:

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