NAT

Add an Additional Layer of Protection with NAT

One of the problems that derive from the attachment of existing IP Networks to the Internet is that local hosts must have globally unique addresses in order to be identified by the backbone routers of the Internet. The Internet routers won't be able to route packets if the IP addresses are not unique. End-users connected to hosts with duplicate addresses cannot be reached and cannot establish application sessions.

The NAT solves the problem by reassigning IP addresses. It contains a pool of available global addresses which are constantly reused . Internal network addresses are allocated according to internal considerations of the Network. Global addresses must remain unique in order to distinguish between different hosts. When a packet is routed, the NAT replaces the internal corporate address with a temporary global address. As soon as the application session is over, the global address is returned to the pool to be reassigned.

NAT in Action

The NAT-enabled router in this diagram has an IP address of 10.25.1.1 for the inside network and an address of 126.22.99.144 for the outside network. Anytime a host on the inside network (10.25.1.x) makes a request to the Internet, the NAT device will translate the 10.25.1.x to 126.22.99.144. The internal machine can directly access any host on the external network, while from the outside, it appears that all outbound traffic is originating from the router’s single IP address.

NAT Advantages:

1. Enhances the level of security within the Network by hiding its internal structure.

2. Permits an almost unlimited number of users of one class C Network address because global addresses are required only when a user is connected to the Internet.

3. When an existing IP Network is attached to the Internet, there is no need to replace the IP address of each and every host on the internal net - the task is accomplished by the NAT.

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