Huawei Quidway S5600 Series Operation Manual page 462

Operation Manual – Multicast Protocol
Quidway S5600 Series Ethernet Switches-Release 1510
V. Assert mechanism
In the shared network such as Ethernet, the same packets may be sent repeatedly. For
example, the LAN network segments contains many multicast routers, A, B, C, and D.
They each have their own receiving path to the multicast source S. As shown in Figure
7-2:
RouterA
Figure 7-2 Diagram for assert mechanism
When Router A, Router B, and Router C receive a multicast packet sent from the
multicast source S, they will all forward the multicast packet to the Ethernet. In this case,
the downstream node Router D will receive three copies of the same multicast packet.
In order to avoid such cases, the Assert mechanism is needed to select one forwarder.
Routers in the network select the best path through sending Assert packets. If two or
more paths have the same priority and metric to the multicast source, the router with
the highest IP address will be the upstream neighbor of the (S, G) entry, which is
responsible for forwarding the (S, G) multicast packets. The unselected routers will
prune the corresponding interfaces to disable the information forwarding.
7.1.3 Introduction to PIM-SM
Protocol independent multicast sparse mode (PIM-SM) is a sparse mode multicast
protocol. It is generally used in the following occasions where:
Group members are sparsely distributed
The range is wide
Large scaled networks
In PIM-SM, all hosts do not receive multicast packets by default. Multicast packets are
forwarded to the hosts which need multicast packets explicitly.
Mulicast packets f orwarded by
the upstream node
RouterB
Assert
Assert
SPT
RouterD
Huawei Technologies Proprietary
RouterC
Assert
Receiv er
7-4
Chapter 7 PIM Configuration