Common Pim Configuration - 3Com 7757 Configuration Manual

Common PIM
Configuration
Figure 117 Diagram for multicast source registration
Source
DR
Server
SPT
Join message
Register message
Multicast packets
When RP receives the registration information from S, it will decapsulate the
registration information and forward the multicast information to the receiver
along RPT, and on the other hand, it will send (S, G) join messages to S hop by
hop. The passed routers constitute a branch of SPT. The multicast source S is the
root of SPT and RP is the destination of RP.
The multicast information sent by the multicast source S will reach RP along the
built SPT, and then RP will forward the multicast information along the built RPT.
Switching RPT to SPT
When the multicast router nearest to the receiver detects that the rate of the
multicast packet from RP to the multicast group G exceeds the threshold value, it
will send (S, G) join messages to the upper-layer router 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 SPT is built.
Then, the last hop router sends Prune message with the RP bit to RP hop by hop.
When RP receives the message, it will reversely forward the Prune message to the
multicast source. Thus, the multicast information stream is switched from RPT to
SPT.
After the switch from RPT to SPT, the multicast information will be sent from the
multicast source S to the receiver directly. Through the switching from RPT to SPT,
PIM-SM can build SPT in a more economical way than PIM-DM.
The related threshold values are not set on Switch 7750 Ethernet switches. When
the switch receives multicast data forwarded along RPT, it will update the input
interface automatically and sends Prune messages to RP.
You can configure the PIM feature of the switch in interface view. The
configuration includes:

Common PIM Configuration

RP
469
Host A
Receiver
Host B
Receiver
Host C