Saturday, August 23, 2008

How NAT is configured

As you are going through this topic, you are surely connected to the Internet and it’s for sure that you are in Network Address Translation (NAT) environment.

The Internet has gone bigger than ever imagined. You must be amazed to know the size of the Internet with NAT. To communicate on the internet every computer and web server must have a public IP address. An IP address is a unique 32-bit number. It specifies your location on global network.

When 32 bit IP (IPv4) addressing first came out, theoretically it can have 4,294,967,296 unique addresses (232). The actual number of available addresses is much smaller because of the way that the addresses are separated into ‘Classes’ and the need to set aside some of the addresses for multi-casting, testing or other specific use. (I will be posting on IP address classes very shortly.)

Network Address Translation is a single device like a router which acts as liaison between the Internet and a local network. One single unique IP address is required to represent your network of computers in a particular company.

Static NAT – Mapping an unregistered IP address to a registered IP address on a one-to-one basis. This is particularly useful when a device needs to be accessed from outside the network.

Dynamic NAT – Maps an unregistered IP address to a registered IP address from a group of registered IP addresses. Dynamic NAT also establishes a one-to-one mapping between unregistered and registered IP addresses but the mapping could vary depending on the registered addresses available in the pool at the time of communication.

Overloading – A form of dynamic NAT that maps multiple unregistered IP addresses to a single registered IP address by using different ports. It is also known as PAT (Port Address Translation), Single Address NAT or Port-Level Multiplexed NAT.

In my upcoming post I’ll let you know on "How your web request from your PC gets served as web page?"

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