Address Translation; Overview; Nat - D-Link DFL-1600 User Manual

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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
Chapter 14. IP Rules