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| 7.3 |  | Routing Multicast Traffic |
| 7.3.7 |  | Protocol independent multicast dense mode |

Protocol Independent Multicast (PIM) gets its name from the fact that it is IP routing protocol independent. That is, regardless of which unicast routing protocol(s) is (are) used to populate the unicast routing table (including static routes), PIM uses this information to perform multicast forwarding; hence, it is protocol independent. Although we tend to refer to PIM as a multicast routing protocol, it actually uses the existing unicast routing table to perform the Reverse Path Forwarding (RPF) check function instead of maintaining a separate multicast route table. Because PIM doesn't have to maintain its own routing table, it doesn't send or receive multicast route updates like other protocols, such as Multicast Open Shortest Path First (MOSPF) or Distance Vector Multicast Routing Protocol (DVMRP). By not having to send multicast route updates, the PIM overhead is significantly reduced in comparison to other multicast protocols.

PIM DM is similar to DVMRP. This protocol works best when there are numerous members belonging to each multimedia group. PIM floods the multimedia packet out to all routers in the network and then prunes routers that do not support members of that particular multicast group.

PIM dense mode is most useful when:

- Senders and receivers are in close proximity to one another
- There are few senders and many receivers
- The volume of multicast traffic is high
- The stream of multicast traffic is constant