Network Address Translation(NAT) is a topic which we all have come across one time or the other. In this Blog post, I am going to explain what exactly is Network Address Translation and how it works (with diagrams).
Network Address Translation (NAT) is a Procedure or a Method wherein a system remaps an IP Address Space into another by modifying Network Address information in the IP header of packets. It is Similar to Classless Inter-Domain Routing (CIDR). The original intention for NAT was to slow the depletion of available IP address space by allowing many private IP addresses to be represented by some smaller number of public IP addresses.
Some uses of Network Address Translation:
– Network Migration and mergers.
– Server Load Sharing.
– Most important “Creating Virtual Servers”
– Make the process of changing ISP hassle free for organisations.
– You can merge two Intranets with duplicate addresses.
Types of Network Address Translation:
1. Static NAT: Also known as SNAT, it is designed to allow one-to-one mapping between local and global addresses. But, the static version requires you to have one real Internet IP address for every host on your network.
2. Dynamic NAT: DNAT, This version gives you the ability to map an unregistered IP address to a registered IP address from a pool of registered IP addresses. You don’t have to statically configure your router to map an inside-to-an-outside address as you would using static NAT, but you do have to have enough real, bona fide IP addresses for everyone who’s going to be sending packets to and receiving them from the Internet.
3. Overloading : This is the most popular type of NAT configuration. Over- loading really is a form of dynamic NAT that maps multiple unregistered IP addresses to a single registered IP address—many-to-one—by using different ports.
Working:
When a host(local) sends an outbound packet to the last router which is configured with NAT. The router identifies the IP address as an inside local IP address destined for an outside network, translates the address, and documents the translation in the NAT table.
The packet is sent to the outside interface with the new translated source address. The external host returns the packet to the destination host, and the NAT router translates the inside global IP address back to the inside local IP address using the NAT table. This is a simple process!
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