Pim configuration, Pim overview, Introduction to pim-dm – H3C Technologies H3C SecPath F1000-E User Manual
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PIM Configuration
When configuring PIM, go to these sections for information you are interested in:
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NOTE:
The term “router” in this document refers to a network device running an IP routing 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.
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).
NOTE:
To facilitate description, a network comprising PIM-capable routers is referred to as a “PIM
domain” in this document.
Introduction to PIM-DM
PIM-DM is a type of dense mode multicast protocol. It uses the “push mode” for multicast forwarding, and
is suitable for small-sized networks with densely distributed multicast members.
The basic implementation of PIM-DM is as follows:
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PIM-DM assumes that at least one multicast group member exists on each subnet of a network, and
therefore multicast data is flooded to all nodes on the network. Then, branches without multicast
forwarding are pruned from the forwarding tree, leaving only those branches that contain receivers.
This “flood and prune” process takes place periodically, that is, pruned branches resume multicast
forwarding when the pruned state times out and then data is re-flooded down these branches, and
then are pruned again.