Cisco Router Configuration Handbook, Second Edition

Appendix I. Well-Known IP Multicast Addresses

Some client server applications use a multicast packet in order to send large streams of data to many hosts with a single transmission. The multicast packet uses special addressing at Layer 3 and Layer 2 to communicate with clients that have been configured to receive these packets. The multicast packet contains a Class D IP address to specify the group of devices that are to receive the packet. This group is known as the multicast group and the IP address translates directly to an Ethernet multicast address. The Ethernet multicast address has the first 24 bits set to 01-00-5E, the next bit is set to 0, and the last 23 bits set to match the low 23 bits of the IP multicast address. Figure I-1 shows ...