PIM Dense Mode (PIM-DM)
James Aweya · 2024
Chapter 4 solely focuses on PIM-DM, a multicast routing protocol designed for network environments where receivers for any multicast group are densely distributed throughout the network. PIM-DM operates on a push model and assumes that every subnet in the multicast domain has at least one receiver interested in the multicast traffic being sent. In other words, PIM-DM operates under the assumption that most subnets and hosts in the network will be interested in any given multicast traffic. Therefore, PIM-DM starts by pushing or flooding multicast traffic to all points in the network; initially, PIM-DM sends multicast traffic to all subnets and hosts in the network. Subsequently, PIM-DM routers that do not have any interested receivers will send PIM Prune messages to remove themselves from the multicast distribution tree. PIM-DM is based on an implicit join model, and routers use the flood-and-prune method to deliver multicast traffic to all parts of the PIM-DM domain and to determine which parts of the network have no interested receivers. PIM-DM uses source-based multicast distribution trees and maintains a multicast forwarding state in the form (S, G), where S is the IP address of the multicast source, and G is the multicast group address.