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What is Network Address Translation (NAT)?

WHAT IS NAT?

Popularly known as NAT, Network Address Translation is a service that converts a private IP address to a public IP address and vice versa. Until now we have learned how every device that uses the Internet has its IP address.

We have learned about the types of IP addresses, one of them being IPv4 addressing. Imagine if all the devices want their own unique IPv4 addresses. We will run out of unique public IP addresses so fast!

The blame is on the fact that an IPv4 address is only a 32-bit long IP address, therefore there are only 4 billion unique IP addresses. This is why we needed some other alternative to this problem of exhaustible IP addresses!

All thanks to the Network Address Translation (NAT) service. In this blog, we will learn the following Concept:

  • Basics of NAT
  • How the NAT service works
  • The types of NAT 
  • The architecture of NAT

Note: If you haven’t read the previous blog of our CCNA 200-301 series, I highly recommend you do so. 

Let us start learning about NAT!

What is NAT (Network Address Translation)?

Network Address Translation, popularly known as NAT, is an outstanding service present in a router. The process of Network Address Translation involves the conversion of private or local IP addresses into global IP addresses and vice versa.

What is Network Address Translation (NAT)?

How Does a NAT Service Work? Here’s an Example!

Let us try to understand NAT in a better way with the help of an example. Suppose that you run a company of your own and you need public IPs for your devices. But you can only get one public ID for your company, which in this example is, 150.150.0.1.

NAT Service Work

Now, there would be a private network formed along with other devices in your company. If any one host posts a request to visit, for example, facebook.com, the packet would travel from the host with a private IP address, 10.0.0.1 which will be converted by the NAT to the source public IP address of the company, 150.150.0.1. This here is the source IP address.

The destination IP address will be that of facebook.com, which is, 200.100.10.1. When the response is taken back, the source IP address becomes that of Facebook, which is 150.150.0.1, and the destination IP address becomes the public IP address of the company, which is 10.0.0.1.

All of this is recorded in a NAT Translation Table. A NAT translation table would look as such for the above example.

Inside Local IP Address

Inside Global IP Address

Outside Global IP Address

10.0.0.1

150.150.0.1

200.100.10.1

 

<<<TRANSLATION BY NAT>>>

 

You must know that the NAT Translation Table also stores the port numbers of the local IP address and global IP addresses.

Note: the server does not understand the private IP address of the source host. It only understands the public IP address presented by the NAT present in the router.

What are the Types of NAT?

There are three types of Network Address Translation. These three types are the methods by which we can configure NAT. The types are as follows:

  • Static NAT
  • Dynamic NAT
  • NAT Overloading or Port Address Translation (PAT)

1. Static NAT:

  • Static NAT is the most basic NAT.
  • It is the process of one-to-one mapping one local IP address with a global IP address.
  • This type of NAT configuration is not really used.
  • This type of NAT serves no purpose at all because you are not able to preserve anything at all.
  • This NAT is only applicable if only one person accesses the Internet at a time in a building. This is not a real-life case.

2. Dynamic NAT:

  • It is a NAT configuration process in which the NAT dynamically assigns publicly registered or publicly available IP addresses to the host that sends the request in the first place to the NAT.
  • The drawback of dynamic NAT is that only a fixed number of public IP addresses are available in a particular period of time.
  • For example, if 20 Data Engineers work in your company for the first 5-hour shift, the request of the 21st Data Engineer will be dropped!

3. NAT Overloading or Port Address Translation (PAT):

  • In the NAT overloading configuration method, we further make use of the publicly reserved IP addresses for the company based on the ports.

For example, if a particular Data Engineer wants to access the Internet, the NAT will assign a specific port using a Port Address Translation (PAT) table.

PAT table
  • In the PAT table, that particular request will be mapped with a specific port.
  • In such a case, a particular publicly registered IP address can cater to multiple private IP addresses on multiple ports.
  • This method provides us more flexibility to use publicly registered IP addresses.

What Does the NAT Architecture Look Like?

By now, you must be familiar with the NAT architecture, yet, let’s again look at it briefly.

The NAT architecture consists of two realms:

  • The inside realm
  • The outside realm
NAT architecture

The inside realm consists of the hosts or devices with private IP addresses. The outside realm consists of the server. 

The host request travels from the source with a private IP address and it gets converted to a public IP address while reaching the destination IP address via the NAT. Therefore, the NAT functions in a straight line.

What are the Limitations of the NAT?

Let us talk about the limitations of NAT. These are

  • The basic idea of the Internet is end-to-end connectivity. The NAT disrupts this connectivity.
  • Protocols like TCP/UDP can be interrupted while using NAT.
  • The NAT could make the VPN tunneling process very complex.
  • Some applications do not function when NAT is enabled.

Conclusion:

NAT is a well-proved solution for stopping the depletion of IPv4 addresses. However, with the takeover of the IPv6 addresses in the upcoming years, there will be no such need for NAT configurations.

NAT is a useful process but it also has its limitations as discussed above. You can also learn about the Network Time Protocol (NTP) here.

Stay tuned for the upcoming blog of our CCNA 200-301 series. 

Happy learning!

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