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PIM Dense Mode

PIM dense mode is less sophisticated than PIM sparse mode. PIM dense mode is useful for multicast LAN applications, the main environment for all dense mode protocols.

PIM dense mode implements the same flood-and-prune mechanism that DVMRP and other dense mode routing protocols employ. The main difference between DVMRP and PIM dense mode is that PIM dense mode introduces the concept of protocol independence. PIM dense mode can use the routing table populated by any underlying unicast routing protocol to perform reverse-path-forwarding (RPF) checks.

Internet service providers (ISPs) typically appreciate the ability to use any underlying unicast routing protocol with PIM dense mode because they need not introduce and manage a separate routing protocol just for RPF checks. Unicast routing protocols extended as multiprotocol BGP (MBGP) and Multitopology Routing in Intermediate System-to-Intermediate System (M-ISIS) were later employed to build special tables to perform RPF checks, but PIM dense mode does not require them.

PIM dense mode can use the unicast routing table populated by Open Shortest Path First (OSPF), IS-IS, BGP, and so on, or PIM dense mode can be configured to use a special multicast RPF table populated by MBGP or M-ISIS when performing RPF checks.

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