R21xx-HP FlexFabric 11900 IP Multicast Configuration Guide

Table Of Contents

Figure 29 Multicast source registration

As shown in Figure 29, the multicast source registers with the RP as follows:

1. The multicast source S sends the first multicast packet to the multicast group G. When receiving the

multicast packet, the source-side DR encapsulates the packet in a PIM register message and

unicasts the message to the RP.

2. After the RP receives the register message, it decapsulates the register message and forwards the

by hop toward the multicast source. The routers along the path from the RP to the multicast source

constitute an SPT branch, and each router on this branch creates an (S, G) entry in its forwarding

table. The source-side DR is the root of the SPT, and the RP is the leaf of the SPT.

3. The subsequent multicast data from the multicast source are forwarded to the RP along the

established branch, and the RP forwards the data to the receivers along the RPT. When the

multicast data reaches the RP along the SPT, the RP unicasts a register-stop message to the

source-side DR to prevent the DR from unnecessarily encapsulating the data.

Switchover to SPT

CAUTION:

If the switch is an RP, disablin

switchover to SPT mi

ht cause multicast traffic forwardin

failures on the

source-side DR. When disabling switchover to SPT, be sure you fully understand its impact on your

network.

In a PIM-SM domain, only one RP and one RPT provide services for a specific multicast group. Before the

switchover to SPT occurs, the source-side DR encapsulates all multicast data addressed to the multicast

group in register messages and sends them to the RP. After receiving these register messages, the RP

decapsulates them and forwards them to the receivers-side DR along the RPT.

Switchover to STP has the following weaknesses: