H3C S7500 Series Operation Manual page 482

Operation Manual – Multicast
H3C S7500 Series Ethernet Switches
Only one BSR can be elected in a network or management domain, while multiple
candidate BSRs (C-BSR) can be configured. In this case, once the BSR fails, other
C-BSRs can elect a new BSR through auto-election. Thus, the service is prevented
from being interrupted.
In the same way, multiple C-RPs can be configured in a PIM-SM domain, the RP
corresponding to each multicast group is figured out through the BSR mechanism.
IV. RPT establishing
Assume the receiver hosts are User B, and User C. When a receiver host joins in a
multicast group G, it will inform the leaf router directly connected to the host through
IGMP messages. Thus the leaf router masters the receiver information of the multicast
group G, and then the leaf router will send join messages to the upstream nodes in the
direction of RP, as shown in
Source
Server
Figure 7-5 Diagram for RPT establishing in PIM-SM
Each router on the path from the leaf router to the RP will generate (*, G) entries in the
forwarding table. The routers on the path form a branch of the RPT. A (*, G) entry
represents the information from any source to the multicast group G. The RP is the root
of the RPT and the receivers are leaves of the RPT.
When the packet from the multicast source S to the multicast group G passes by the RP,
the packet will reach the leaf router and receiver host over the established path in the
RPT.
When the receiver is not interested in the multicast information any more, the multicast
router nearest to the receiver will send a prune messages to the RP hop by hop in the
direction reverse to the RPT. When the first upstream router receives the prune
message, it will remove the links to the downstream router from the interface list and
Figure
RP
RPT
Join message
Multicast packets
7-5:
7-8
Chapter 7 PIM Configuration
Host A
Receiver
DR
Host B
DR
Receiver
Host C