5.7 Multicast and Link Protocol

So far we have been describing broadcast transmission, but the problem with LAN is identifying the link address of the recipient.

The ARP protocol specifies an unambiguous relationship between an unambiguous IP address (unicast) and the destination link address. This is possible when an unambiguous relationship exists between IP addresses and link addresses. This relationship is called mapping (mapping of IP addresses to link addresses).

The situation is different when a broadcast is sent to all LAN systems. For these purposes the link protocol uses a broadcast, which for the Ethernet, FDDI, and so on is ff:ff:ff:ff:ff:ff.

But how do we do this with multicasts that are addressed neither to one destination on the LAN nor to all systems on the LAN, but rather to several particular destinations?

First let’s look at the problem. Under normal circumstances, the recipient processes only those frames that are broadcasts or addressed with the destination link...