In Section 
we have already seen that a special range
(Class D) of the IP address space has been reserved for IP multicast
host group addresses. As with unicast IP addresses, a number of
well known addresses have been defined that are used by
applications and support protocols (see Section ). The
STD 2 of the IETF [IANA94] lists a whole range of these well known
addresses, the most important of which are the addresses: 224.0.0.1 and
224.0.0.2, all IP multicast capable hosts and all mrouters
respectively.
Normal IP uses ARP to resolve unicast IP addresses to Ethernet
addresses. With IP multicasting there must also be a mapping from the IP
multicast address to the LAN equivalent. On an Ethernet LAN, an
algorithm can be used to map an IP multicast address directly to an
Ethernet multicast address
. If a LAN is used on which it is
not possible to do the translation algorithmically, a dynamic address
resolution service will be used. This could resemble the ARP protocol, or
it may use some other means to resolve the IP host group address to the
LAN equivalent.