Dell PowerConnect 8100 CLI Reference Guide - Page 1145

51 Multicast Commands The PowerConnect Multicast component is best suited for video and audio traffic requiring multicast packet control for optimal operation. The Multicast component includes support for IGMPv2, IGMPv3, PIM-DM, PIM-SM, and DVMRP. Communication from point to multipoint is called Multicasting. The source host (point) transmits a message to a group of zero or more hosts (multipoint) that are identified by a single IP destination address. Although the task may be accomplished by sending unicast (pointto-point) messages to each of the destination hosts, multicasting is the more desirable method for this type of transmission. A multicast message is delivered to all members of its destination host group with the same bestefforts reliability as regular unicast IP messages. The message is not guaranteed to arrive intact at all members of the destination group or in the same order relative to other messages. The advantages of multicasting are explained below: • Network Load Decrease: A number of applications are required to transmit packets to hundreds of stations. The packets transmitted to these stations share a group of links on their paths to their destinations. Multicast transmission can conserve much needed network bandwidth, since multicasting transmission requires the transmission of only a single packet by the source and replicates this packet only if it is necessary (at forks of the multicast delivery tree). • Discovery of resources: A number of applications require a host to find out whether a certain type of service is available. Internet protocols such as Bootstrap Protocol (BOOTP) and Open Shortest Path First (OSPF) protocol are among these applications. Using multicast messages and sending the query to those hosts which are potentially capable of providing this service speeds the gathering of this information considerably. Although a group of hosts residing on the same network are the intended target for the majority of multicast packets, this limitation is not mandatory. Discovering the local domain-name server is the intended use of multicast messages on remote networks when there is less than one server per network. Multicast Commands 1145