Chapter 13. IGMP: Internet Group Management Protocol

Introduction

Section 12.4 provided an overview of IP multicasting and described how class D IP addresses are mapped into Ethernet addresses. We briefly mentioned how multicasting occurs on a single physical network, but said complications occur when multiple networks are involved and the multicast datagrams must pass through routers.

In this chapter we'll look at the Internet Group Management Protocol (IGMP), which is used by hosts and routers that support multicasting. It lets all the systems on a physical network know which hosts currently belong to which multicast groups. This information is required by the multicast routers, so they know which multicast datagrams to forward onto which interfaces. ...

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