H3C S7500 Series Operation Manual page 483

Operation Manual – Multicast
H3C S7500 Series Ethernet Switches
check whether it has the receivers interested in the multicast information. If not, the
upstream router will continue to forward the prune message to upstream routers.
V. Multicast source registration
In order to inform the RP about the existence of multicast source S, when multicast
source S sends a multicast packet to the multicast group G, the router directly
connected to S will encapsulate the received packet into a register message and
unicast it to the corresponding RP, as shown in
Source
Server
Figure 7-6 Diagram for SPT establishing in PIM-SM
When the RP receives the register message from S, it will decapsulate the register
message and forward the multicast data to the receiver over the RPT, and on the other
hand, it will send a (S, G) join message to S hop by hop. The passed routers constitute
a branch of the SPT. The multicast source S is the root of the SPT and the RP is the
destination of the SPT.
The multicast data sent by the multicast source S will reach the RP over the established
SPT, and then the RP will forward the multicast data along the established RPT.
VI. RPT-to-SPT switchover
When the multicast router nearest to the receiver detects that the rate of multicast
packets from the RP to the multicast group G exceeds the threshold value, it will send
an (S, G) join message to the upper-layer router in the direction of the multicast source
S. The join message reaches the router nearest to the multicast source (namely, the
first hop router) hop by hop and all the passed routers have the (S, G) entry. As a result,
a branch of the SPT is established.
DR RP
SPT
Join message
Register message
Multicast packets
Figure 7-6:
7-9
Chapter 7 PIM Configuration
Host A
Receiver
Host B
Receiver
Host C