IP implementations exist on a variety of LAN technologies. Not all those
technologies implement an efficient multicasting method. The level of
multicast support varies from almost ideal to no support at all (Ethernet and
ATM
respectively). The IP multicast must be mapped onto the
network interface layer's functions.
In Section 
, it has been shown that even if lower protocol
layers do not support multicasting, a higher layer can be provided with
a multicast service. What kind of adaption is needed to provide that
kind of support depends on the possibilities of the network technology
used.
In a broadcast oriented network technology, like Ethernet and Token-Ring, the copying of data is done automatically (even with unicast transmissions!). Nodes that want a copy can simply take it from the network bus. With a non-broadcast network technology, like ATM or X.25, a more explicit copying process must be used. This explicit copy can be done at any level between the peer IP entities, the lower in the protocol stack the better. E.g. ATM has a point-to-multipoint service (see chapters 4 and 5), which can be used to some extent for IP multicasting.