Chapter 21. Multicasting

Introduction

As shown in Figure 20.1, a unicast address identifies a single IP interface, a broadcast address identifies all IP interfaces on the subnet, and a multicast address identifies a set of IP interfaces. Unicasting and broadcasting are the extremes of the addressing spectrum (one or all) and the intent of multicasting is to allow addressing something in between. A multicast datagram should be received only by those interfaces interested in the datagram, that is, by the interfaces on the hosts running applications wishing to participate in the multicast group. Also, broadcasting is normally limited to a LAN, whereas multicasting can be used on a LAN or across a WAN. Indeed, applications multicast across a subset ...

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