What is NAT – Network Address Translation

NAT (Network Address Translation) used to reduce the requirement of the Public IP address and increase security of Internal Computer Networks. NAT is a method in which Internal Network IP address translate into Public IP address before reach to external Network (Internet). Means that Its translate Private IP address into Public IP address and Public IP address into Private IP address. NAT used to Connect a device with Private IP address to the Internet. With the help NAT you can hide an organization internal network from external network (Internet). So that Internet user can’t able to see any systems IP address behind of the NAT.

Private IP address used in an organizational internal network. Any device can’t access internet from Private IP address because Private IP address is not routable on the Internet. Public IP address is routable on the internet so that we need NAT. Router and Firewall is a device which is used for Network Address Translation.

Network Address Translation


Read Also



Advantage of NAT

  • Access Internet from Private IP address
  • Security – Hide Internal Network from Internet
  • Publish Server Over Internet
  • Overlapping network
  • Avoid Routing
  • Save cost to save public IP address.

In below Image, You can see that Multiple Private IP address from internal Network can Access Internet with Single Public IP Address. Means that Multiple Private IP address can be translated into Single Public IP address.



Type of NAT (Network Address Translation)

Static NAT

Static NAT provide one to one mapping, Means that A Single Private IP address will be translate to a single Public IP address. Which always will be static. Its used when Internal Network (Private Network) want to access external Network. There is required specific Public IP address for every Private IP address. Suppose there is 100 System in your Internal Network want to access Internet then you required 100 Public IP address. As we know that Public IP address is too costly so not possible to purchase 100 valid IP address.

Network Address Translation

static NAT

Dynamic NAT

In Dynamic NAT, Private IP address translated into available Pool of Public IP address. In Dynamic NAT,  Mapping is random with Public IP address not static. Means that for another session Private IP address may translate with another Public IP address from the Pool. These Pool of Public IP address define by ISP for External Network. Dynamic NAT assists to secure a network as it hide the internal configuration of Private network. Its Map Private IP to Public IP on the basis of first come first serve.

Network Address Translation

Dynamic NAT

PAT (Port Address Translation)

PAT is also knows a Overloading NAT, Which provide many to one mapping. Means that Multiple Private IP address can be translated into single public IP address using port number. A Unique port number mapped along with Public IP address for unique Private IP address. Dynamic PAT uses dynamically assign port number to identify the original source IP Address. NAT Device (Router or Firewall) uses requested service port number to reach the correct destination server.

Network Address Translation

How Dynamic PAT Works

Original Source Original DestinationTranslated SourceTranslated Destination



Above table you can see, When you trying to access destination (web server) on port 80 from source with source port 1025. Then Source address translated into public IP address and port translated into 3001. Now when Web Server reply then destination will be for Private IP address ( 

Related Post


Share This onShare on FacebookTweet about this on TwitterShare on LinkedInShare on RedditShare on StumbleUponShare on Google+Pin on PinterestBuffer this pageDigg thisShare on Tumblr
Rakesh Kumar
Rakesh Kumar is a Network engineer and a Blogger. He is crazy for learn and write about Technology , Tech and Computer Tips and Tricks Blog.

Leave a Reply