Content

| 7.3 |  | Routing Multicast Traffic |
| 7.3.5 |  | Multicast Routing Protocols |

Dense Mode
A multicast routing protocol is responsible for the construction of multicast delivery trees and enabling multicast packet forwarding. Different IP multicast routing protocols use different techniques to construct multicast spanning trees and forward packets.

IP multicast routing protocols generally follow one of two basic approaches, depending on the distribution of multicast group members on the network.

The first approach is based on the assumption that the multicast group members are densely distributed throughout the network and bandwidth is plentiful, meaning that almost all hosts on the network belong to the group. These dense-mode multicast routing protocols rely on periodic flooding of the network with multicast traffic to set up and maintain the distribution tree.

Dense-mode routing protocols include the following:

- Distance Vector Multicast Routing Protocol (DVMRP)
- PIM Dense Mode (PIMDM)
- Multicast Open Shortest Path First (MOSPF)

Dense-mode protocols employ only shortest-path trees (SPTs) to deliver (S, G) multicast traffic using a push principle. The push principle assumes that every subnet in the network has at least one receiver of the (S, G) multicast traffic, and therefore, the traffic is pushed or flooded to all points in the network. This process is analogous to a radio or TV broadcast that is transmitted over the air to all homes within the coverage area. Receivers simply need to tune in to the broadcast to receive the program.

The DM protocols are most appropriate in environments with densely clustered receivers and the bandwidth to tolerate flooding. An example of when a DM protocol may be used is when a CEO of a company wants to broadcast a message to all employees within the headquarters campus network.