TCP/IP Guide

IP Multicast Addressing

The vast majority of traffic on IP internetworks is unicast, which is one source device sending to one destination device. IP also supports multicasting, which is a source device sending to a group of devices. Multicasting is not used a great deal on the present-day Internet, mainly due to a lack of widespread hardware support, though it is useful in certain circumstances, especially as a more efficient alternative to broadcasting.

The classful IP addressing scheme sets aside one-sixteenth of the address space for multicast addresses as Class D. Multicast addresses are identified by the pattern 1110 in the first four bits, which corresponds to a first octet of 224 to 239. Thus, the full range of multicast addresses is from ...