Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureHard
A network architect is designing a multicast solution for a video conferencing system that needs to operate across multiple VLANs and subnets within an enterprise. The solution must ensure that multicast traffic is only forwarded to segments where active receivers exist, to conserve bandwidth and prevent flooding. Which Layer 3 multicast routing protocol should be implemented to achieve this efficient, receiver-driven distribution?
- AOpen Shortest Path First (OSPF)
- BDistance Vector Multicast Routing Protocol (DVMRP)
- CInterior Gateway Routing Protocol (IGRP)
- DProtocol Independent Multicast - Sparse Mode (PIM-SM)
Show answer & explanationAnswer & explanation
Correct answer: D. Protocol Independent Multicast - Sparse Mode (PIM-SM)
PIM-SM (Protocol Independent Multicast - Sparse Mode) is the most common and efficient Layer 3 multicast routing protocol for enterprise networks. It uses a receiver-driven model, where receivers explicitly join multicast groups, and traffic is forwarded only to segments with active group members, significantly conserving bandwidth and preventing flooding.
Why the other options are wrong
- A. OSPF is a link-state unicast routing protocol and does not directly support multicast routing (though it can be used to provide the underlying unicast routing for PIM).
- B. DVMRP is an older, dense-mode multicast routing protocol that floods multicast traffic throughout the network and then prunes branches without receivers, which is inefficient for sparse environments.
- C. IGRP is a distance-vector unicast routing protocol and does not support multicast routing.
PIM-SM (Protocol Independent Multicast - Sparse Mode)
A Layer 3 multicast routing protocol that efficiently routes multicast traffic in networks where receivers are sparsely distributed, using a receiver-driven model.
- Receiver-driven (explicit join).
- Uses a Rendezvous Point (RP) for initial joins.
- Builds shared trees and then switches to shortest-path trees.
- Efficient for sparse environments, conserves bandwidth.
Memory trick: PIM-SM is like a smart TV subscription: only send the channel to those who want it.