 <h3>As for IPv4 -- it's similar in IPv6</h3> <p><strong>Multicast addresses</strong> Theses correspond to the class D. The class D:</p> <ul> <li>First octet: 224 - 239</li> <li>First octet pattern: 1110*</li> <li>These IP addresses are multicast addresses.</li> </ul> <p>there are used for specific (routing protocol, service discovery, NTP), sometimes experimental, use-cases.</p> <p>Network nodes must perform a <em>join(multicast-address)</em> call in order to receive packet sent to the address <em>multicast-address</em>. There can be many multicast addresses present in a network.</p> <p><strong>Broadcast address</strong></p> <p>There is only <strong>one</strong> broadcast address in every network. This address is constructed with all its host-part IP address bits set to <strong>1</strong>.</p> <p>If the network is 192.168.0.0/24 the last octet is the host-part IP address (and the first three ones are the network-part IP address). The broadcast address is then 192.168.0.<strong>255</strong>.</p> <p>The broadcast address is used to send packet to <strong>all</strong> the nodes within the <strong>LAN</strong>, not further, not only the nodes that would had performed a <em>join(multicast-address)</em> call -- that make no sense.</p> <hr> <p><strong>More details <a href="http://stackoverflow.com/a/7781445/5321002">on this answer</a>.</strong></p>