D-Link DFL-2500 User Guide - Page 131
Address Translation
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112 Chapter 14. IP Rules 14.2 Address Translation 14.2.1 Overview For functionality and security considerations, Network Address translation(NAT) is widely applied for home and office use today. D-Link firewall provides options to support both Dynamic and Static NAT. These two types are represented by the NAT and SAT rule settings respectively. This section explains how NAT works and what it can and cannot do. 14.2.2 NAT What is NAT? When communicating on the Internet, each node needs to register a unique network address to be reachable. But the available unique addresses from the range of IPv4 is very limited while nowadays network is becoming lager and larger. Network address translation (NAT) enables computers on private networks to use a set of unregistered addresses internally, and share one or a set of public IP addresses for external connections to Internet resources. Normally, a router or a firewall located at where the LAN meets the Internet makes all necessary IP address translations. For each NATed network, the private IP address spaces (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are reused. This means that multiple interfaces connected to different networks can have the same address, relieving the pressure of having to use public IPv4 addresses for every node. Why is NAT widely used? In addition to solve the IP shortage problem, NAT is developed to serve many other purposes: • Functionality - Using NAT, there is no need to register an IP address for every computer in a local network. A company can use many internal IP addresses and one registered public IP address to provide Internet services. Since these addresses are used internally only, there is no possibility of address collision with other companies. It allows a company to combine multiple access connections into a single Internet connection. • Security - Computers locating at the local network and using a range of private addresses are not directly accessible from the Internet. To D-Link Firewalls User's Guide
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