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Cloud Native Data Center Networking by Dinesh G. Dutt

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Chapter 8. Multicast Routing

Multicast is a zero billion dollar industry

Fred Baker

Many years ago, when I was still a relative newcomer to the networking field, I heard Fred Baker, then chair of the IETF, declare, “multicast is a zero billion dollar industry”. That declaration still holds in the modern DC. If you want your applications to run in the cloud, forget multicast. However, with enterprise networks beginning to embrace Clos topology, the need for multicast has reared its head again. This is especially true in some deployments involving EVPN (discussed in Chapter 6). The goal of this chapter is to explain the role of multicast routing in the context of the modern data center. We will not get into aspects of multicast routing that have less to do with its specific use case with EVPN.

This chapter will help answer questions like:

  • What is multicast routing and how is it different from unicast routing?

  • Why use multicast?

  • Why is multicast routing frowned upon in the modern DC?

  • How does the central routing protocol for multicast, PIM-SM, work?

  • What adaptations are required to deploy multicast routing in Clos topologies?

We begin with an overview of multicast routing, and the fundamental problems multicast routing is designed to address.

Multicast Routing: Overview

Even though I presume everyone understands what multicast is, let me take a few sentences to explain it. Consider Figure 8-1. There are 7 routers: the leaves L1-L4, the spines S1-S3, and an external ...

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