The number of home users and small businesses that want to use the Internet is ever increasing. The shortage of addresses is becoming a serious problem. A quick solution to this problem is called network address translation(NAT).NAT enables a user to have a large set of addresses（71）and one address, or a smallset of addresses,externally. The traffic inside can use the large set; the traffic（72）, the small set. To separate the addresses used inside the home or business and the ones used for the Internet, the Internet authorities have reserved three sets of addresses as （73）addresses. Any organization can use an address out of this set without permission from the Internet authorities. Everyone knows that these reserved addresses are for private networks.They are （74） inside the organization, but they are not unique globally. No router will （75） a packet that has one of these addresses as the destination address.The site must have only one single connection to the global Internet through a router that runs the NAT software.
