Introduction To Network Address Translation (NAT)

Introduction

Network Address Translation, defined by RFC 1631, is becoming very popular in today's networks as it's supported by almost every operating system, firewall appliance and application. NAT was born thanks to the fast depletion of public IP Addresses, in other words real IP Addresses that can only exist on the Internet.

As IP Addresses are 32 Bit, in theory we could have upto 4,294,967,296 IP Addresses (that's 2^32) ! In practice though the number is a lot smaller, somewhere around 3.2 billion, because of the way the IP Addresses are separated into Classes (Class A, B , C e.t.c) and the need to set aside special addresses for multicasting (also known as Class D), broadcasting and other functions.

You might have heard or read about IPv6. This new addressing scheme has been designed to make sure we don't face the same problem as IPv4, but its implementation requires the modification of the entire Internet infustructure, so don't expect anytime soon to deal with IPv6. Chances are it's going to co-exist with IPv4, since IPv6 isn't the best solution for small to medium sized companies or small private networks.

This exciting section will show, and explain in detail, what NAT is, its different modes and how they work. We will also see how NAT helps protect your network and minimise network security threats.

Oh, and keep in mind...

You should also be up to scratch in your IP Addressing and Subnetting topics. In the following sections, there are new concepts introduced which will require you to a have basic understanding on IP Addressing and Subnetting. Please check the relevant sections if you think you need to brush up on these before proceeding!

There's more to NAT than meets the eye !

When NAT was released, it was created to provide solutions to almost every type of network configuration. This is achieved by the various modes in which NAT can function. Depending on your network structure, your available real (public) IP Addresses and the results you need, you can enable NAT in 3 different modes! Now don't assume it's hard to understand this cool stuff, cause I'm telling you it's definitely not! Once you get the hang of the NAT Concept, the rest is easy to digest, even late at night :)

So What's Covered ?

As with most cool networking topics, it's impossible to cover NAT on one page and if you happen to find another site that covers NAT in one page, I assure you you're missing out on a lot of important information, so stick to Firewall.cx :)

With all this in mind, I've split NAT into 6 sections. Each section deals with a particular NAT mode or NAT topic, giving you an in-depth look on how each NAT mode works using a few examples, and its advantages over the rest available NAT modes. The information provided has been carefully selected and written to make sure it covers all ranges of user levels, meaning from intermediate to advanced.

Section 1: NAT Concepts. A good introduction to NAT followed by its basic functions, how it works and which devices in a network usually implement NAT. Simple, clear and colourful diagrams will ensure you grasp this concept without any trouble.

Section 2: NAT Table. This section will introduce the NAT Table, which is the heart of NAT. Here you will learn the purpose of the NAT table, where it's stored along with a lot of other interesting information.

Section 3: Static NAT Mode. Learn what Static NAT is and how it functions. Two pages of detailed diagrams, well thought examples and their analysis along with other rich information ensures you will learn everything there is about Static NAT.

Section 4: Dynamic NAT Mode. Learn what Dynamic NAT is and how it functions. Simple diagrams are available to help you understand how Dynamic NAT works and what its advantages are over Static NAT. Dynamic NAT is analysed over two pages using examples and step by step analysis, ensuring to capture all the required information and answer every question you might have.

Section 5: NAT Overload Mode. Also known as IP Masquerading (in the Linux world), Port Address Translation (PAT) or Dynamic NAT with PAT. Discover the most common NAT mode for small networks. This NAT mode is used by most Internet sharing software. This section will help you understand how NAT Overload works and what its benefits are over the rest. Again, simple diagrams have been designed to make sure you grasp all this cool stuff :)

Section 6: Advanced NAT (Coming Soon). This pages deals with more advanced NAT concepts and analysis. It contains more detailed and technical information about NAT, thus requires a slightly more advanced level of networking knowledge and TCP/IP. It also outlines security concerns and using NAT through VPN's and other complex network configurations.

The type of NAT mode you choose to use, depends on your network resources, capabilities of your NAT-enabled device and, lastly, your needs. Together we will discover the power of NAT and understand why its become so popular.

Next - NAT Concepts