Summary

IP multicasting is one of those quixotic topics: absolutely indispensable, yet only selectively so. Only a fraction of the networked applications and functions that use IP can benefit from multicasting capabilities. However, that small subset runs the gamut. Uses range from critical router-level functions such as routing table updates in certain routing protocols to some of the Internet's more lighthearted uses, such as music distribution and online gaming.

Despite its reputation, multicasting is not some arcane form of sorcery. It is a logical extension of the capabilities of the IP suite, and it takes advantage of a reserved block of addresses. These reserved addresses can be used to support the development of local and/or global groups of addresses for multicast purposes. Having examined the multicast group addresses, as well as how those group addresses are translated into unique IP addresses, should have helped remove some of the mystery of multicasting.