Typically，an IP address refers to an individual host on a particular  network. IP also accommodates addresses that refer to a group of  hosts on one or more networks.Sunch addresses are referred to as multicast addresses，and the act of  sending a packet from a source  to the  members of  a （作答本题）group is  referred to as multicasting. Multicasting done  （72）    the scope of  a single LAN segment is straight forward. IEEE 802 and other LAN protocols include provision for MAC-level multicast addresses. A packet with a multicast address is transmitted on a LAN segment.Those stations that are members of the （73）multicast group recognize the multicast address and （74）the packet.In this case,only a single copy of the packet is ever transmitted.This technique works because of the （75）nature of a LAN:A transmission from any one station is received by all other stations on the LAN.

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