Chapter 13
IPv6 PIM-SM Configuration
Table of Contents
13.1 PIM-SM Overview
Introduction to PIM-SM
PIM-SM is mainly used in the following situations:
l
Group members locate sparsely in a relatively large scale.
l
The network bandwidth resource is limited.
PIM-SM does not depend on a specific unicast routing protocol. PIM-SM assumes that
all routers on a shared segment do not need to send multicast packets. The routers only
can receive and send multicast packets after they request to join a multicast group on
their own initiative. PIM-SM advertises the multicast information to all routers supporting
PIM-SM through a RP. In PIM-SM, a router joins or leaves the multicast group explicitly.
This reduces the number of packets and the bandwidth used by the control packets.
PIM-SM Principle
PIM-SM sends multicast packets by using a shared tree. A shared tree has a center point
that is responsible for sending packets to all the source-sending ends in the multicast
group. Each source-sending end sends packets to the center point along the shortest
path, and then takes the center point as the root point to distribute the packets to various
receiving ends of the group.
The group center point of the PIM-SM is called the RP. There may be several RPs in a
network, but there is only one RP in a multicast group.
A switch can obtain the location of the RP in two ways.
1.
Configure the RP manually and statically on the switches running PIM-SM.
2.
PIM-SMv2 obtains the location through the candidate RP advertisement.
The
candidate RP with the lowest priority will become formal RPs.
In PIM-SM, some switches running PIM-SM are manually set to work as candidate
Bootstrap switch (
). The candidate BSR with the highest priority will be elected as
the formal BSR.
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