Network Address Translation (NAT) Overview in Win XP

As more and more homes and small businesses add computers, they will find the network is a very powerful computer resource sharing tool. Internet connectivity is a more precious resource on the network and may be shared. To share an Internet connection while using a low-cost, simple-to-manage home or small office network, you need to deploy an Internet gateway. Internet gateways typically use NAT (Network Address Translation) as a way to connect multiple hosts to the Internet to share a single public IP address. But unfortunately, the solution will destroy multiple web applications. We will explain this in this article.

The existing "NAT Traversal" Technology
allows web applications to detect the presence of local NAT devices. Once detected, the application then configures the NAT and defines the appropriate mapping to resolve the compatibility issue.

This article is an overview article that will give users and developers of web applications a brief introduction to NAT, how to identify common NAT issues, and how applications can use NAT Traversal to solve these problems. An important feature of Internet gateway devices that require attention is UPnP authentication. When users purchase or lease Internet gateway devices from a service provider, it is highly recommended that only those devices that pass UPnP authentication for NAT traversal be considered, because this feature is more innovative for meeting users, reducing support costs, and using them. Services and applications are critical.

For gateway device manufacturers, adding UPnP technology to NAT traversal in Internet gateway devices is not complicated, and the cost is not high, and it does not take a lot of time. By using UPnP (already based on Internet standards and protocols), Internet gateway device manufacturers can address NAT traversal issues and extend the benefits to most applications that pass through the device. This is in stark contrast to many application developers or gateway device manufacturers who have to provide a one-time solution to the above problems. This article is not intended to provide a detailed guide for hardware manufacturers who wish to implement NAT Traversal in Internet gateway devices. For this information, see the UPnP Forums Web site.

Knowledge of Windows architecture, networking, and UPnP architecture will be helpful in fully understanding this article, but it is not required.

What is NAT?

Network Address Translation (NAT) is an Internet Engineering Task Force (IETF) standard that allows multiple PCs on a private network (using private address segments such as 10.0.xx, 192.168) .xx, ​​172.xxx) Share the IPv4 address of a single, global route. The growing shortage of IPv4 addresses is a major reason for the frequent deployment of NAT. Internet Connection Sharing in Windows XP and Windows Me and many Internet gateway devices use NAT, especially when connecting to a broadband network via a DSL or cable modem.

NAT solves the problem of IPv4 address consumption (not necessary in IPv6 deployment). Although effective, it is a temporary solution. This IPv4 address occupation problem has become more serious in Asia and other parts of the world, and it is becoming a concern in North America. This is why people have long been concerned about using IPv6 to overcome this problem.

In addition to reducing the required IPv4 addresses, NAT provides a hidden layer for private networks because all hosts outside the private network monitor traffic through a shared IP address. NAT is different from firewall
or proxy server, but it does help with security.

Figure 1: An example of a network that uses a NAT device for Internet communication.
Just as a fixed cable modem or DSL modem can be used as a NAT device, a
PC can also act as a NAT device.