Cloud Native Data Center Networking

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 data center. 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 helps 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 data center?

• How does the central routing protocol for multicast, Protocol-Independent Multicast Sparse Mode, 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 that you understand what multicast is, let me take a few sentences to explain it. Consider Figure 8-1. There are seven routers: ...