User's Manual

UTT Technologies Chapter 8 NAT
http://www.uttglobal.com Page 210
8.3 NAT Rule
8.3.1 Introduction to NAT
The NAT (Network Address Translation) is an Internet standard that is used to map one IP
address space (i.e., Intranet) to another IP address space (i.e., Internet). The NAT is
designed to alleviate the shortage of IP addresses, that is, it allows all the LAN hosts to
share a single or a small group of IP addresses: On the Internet, there is only a single
device using a single or a small group of public IP addresses; but the LAN hosts can use
any range of private IP addresses, and these IP addresses are not visible from the
Internet. As the internal network can be effectively isolated from the outside world, the
NAT can also provide the benefit of network security assurance.
The Device provides flexible NAT features, and the following sections will describe them in
detail.
8.3.1.1 NAT Address Space Definitions
To ensure that NAT operates properly, the Device uses and maintains two address
spaces:
Ɣ Internal IP address: It indicates the IP address that is assigned to a LAN host by the
administrator. It is usually a private IP address.
Ɣ External IP address: It indicates the IP address that is assigned to the Device¶s
Internet connection by the ISP. It is a legal public IP address that can represent one or
more internal IP addresses to the outside world.
8.3.1.2 NAT Types
The Device provides three types of NAT: One2One, EasyIP and Passthrough.
Ɣ One2One (One to One): It indicates static network address translation. It is always
referred to as Basic NAT, which provides a one to one mapping between an internal
and an external IP address. In this type of NAT, IP address need be changed, but port
needn¶t.
One to One NAT can be used to allow the outside users to access a LAN server: In the