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chẳng hạn như một modem dial-up. NAT cũng có thể được sử dụng cho dịch địa chỉ giữa các giao thức khác nhau, trong đó cải thiện an ninh và cung cấp cho khả năng tương tác nhiều hơn trong các mạng không đồng nhất.Hãy nhớ rằng NAT và IPsec có thể không làm việc tốt với nhau. | 92 Chapter 3 Infrastructure Basics For smaller companies NAT can be used in the form of Windows Internet Connection Sharing ICS where all machines share one Internet connection such as a dial-up modem. NAT can also be used for address translation between multiple protocols which improves security and provides for more interoperability in heterogeneous networks. NOTE Keep in mind that NAT and IPsec may not work well together. NAT has to replace the headers of the incoming packet with its own headers before sending the packet. This might not be possible because IPsec information is encrypted. TIP Another address range to keep in mind when designing IP address space is Automatic Private IP Addressing APIPA . In the event that no Dynamic Host Configuration Protocol DHCP server is available at the time that the client issues a DHCP lease request the client is automatically configured with an address from the 169.254.0.1 through 169.254.255.254 range. Subnetting Subnetting can be done for several reasons. If you have a Class C address and 1 000 clients. you will have to subnet the network or use a custom subnet mask to accommodate all the hosts. The most common reason networks are subnetted is to control network traffic. Splitting one network into two or more and using routers to connect each subnet together means that broadcasts can be limited to each subnet. However often networks are subnetted to improve network security not just performance. Subnetting allows you to arrange hosts into the different logical groups that isolate each subnet into its own mini network. Subnet divisions can be based on business goals and security policy objectives. For example perhaps you use contract workers and want to keep them separated from the organizational employees. Often organizations with branches use subnets to keep each branch separate. When your computers are on separate physical networks you can divide your network into subnets that enable you to use one block of addresses .
