3com S7906E Installation Instruction
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PIM Configuration
When configuring PIM, go to these sections for information you are interested in:
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The term “router” in this document refers to a router in a generic sense or a Layer 3 switch running the
PIM protocol.
PIM Overview
Protocol Independent Multicast (PIM) provides IP multicast forwarding by leveraging static routes or
unicast routing tables generated by any unicast routing protocol, such as routing information protocol
(RIP), open shortest path first (OSPF), intermediate system to intermediate system (IS-IS), or border
gateway protocol (BGP). Independent of the unicast routing protocols running on the device, multicast
routing can be implemented as long as the corresponding multicast routing entries are created through
unicast routes. PIM uses the reverse path forwarding (RPF) mechanism to implement multicast
forwarding. When a multicast packet arrives on an interface of the device, it is subject to an RPF check.
If the RPF check succeeds, the device creates the corresponding routing entry and forwards the packet;
if the RPF check fails, the device discards the packet. For more information about RPF, refer to
Multicast Routing and Forwarding Configuration in the IP Multicast Volume.
Based on the implementation mechanism, PIM falls into two modes:
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Protocol Independent Multicast–Dense Mode (PIM-DM), and
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Protocol Independent Multicast–Sparse Mode (PIM-SM).