3Com Switch 8800 Advanced Software V5 Configuration Guide

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PIM CONFIGURATION
When configuring PIM, go to these sections for information you are interested in:
■ “PIM Overview” on page 563
■ “Configuring PIM-DM” on page 575
■ “Configuring PIM-SM” on page 577
■ “Configuring PIM-SSM” on page 586
■ “Configuring PIM Common Information” on page 587
■ “Displaying and Maintaining PIM” on page 592
■ “PIM Configuration Examples” on page 593
■ “Troubleshooting PIM Configuration” on page 604
n
The term "router" in this document refers to a router in a generic sense or a
Switch 8800 running the PIM protocol.
PIM Overview Protocol Independent Multicast (PIM) provides IP multicast forwarding by
leveraging 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
“RPF Mechanism” on page 503.
Based on the forwarding mechanism, PIM falls into two modes:
■ Protocol Independent Multicast-Dense Mode (PIM-DM), and
■ Protocol Independent Multicast-Sparse Mode (PIM-SM).
Presently, the any-source multicast (ASM) model implementations include the
PIM-DM and PIM-SM modes, while the source-specific multicast (SSM) model can
be implemented by leveraging part of the PIM-SM technique.
n
To simplify description, a network comprising PIM-capable routers is referred to as
a "PIM domain" in this document.