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NAT (Network Address Translation)

The increase of the internet users has consumed IPv4 addresses rapidly. And to continue with these addresses various techniques have used by organizations. One of them is Network Address Translation(NAT).

As you know there are public and private addresses. The public addresses are used to reach to the internet, because they can be routed on internet. But the private addresses are used within an organization only, because they can not be routed.

With NAT, we can use private address millions of times all over the world and still can be access to the internet. Here, NAT provide the translation from private address to the publica address.We are connecting internet with our private address, bur in real at the backplane it is doing this with a public address.

Private to public address translation is not the only way that NAT is used. NAT is also used for public to puclic or private to private translations. But the first one is most common.

For securtiy reasons, NAT also provide hiding your network from the outside of the world. Because the remote node that you connect by internet, only knows your public address, not the real internal address of your pc.

There are types of NAT.These are:

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

Static NAT is the type that is used for one-to-one translation of ports or addresses,

Dynamic NAT is the type that is used with a public address pool, and works with more than one public address,

PAT is the type that translates the outbound traffic of internal nodes to unique port numbers of a single public address.

By the way, there are some terms that we must explain. These are:

Inside local : Your PC’s private address,
Inside global : Public address assigned to your PC,
Outside local : Outside host’s public address,
Outside global: Same address as the outside local, necessary to translate an outside address to an private address.

Let’s explain this situation with an example.

nat (network adress translation) inside local inside global outside local outside global

NAT (Network Adress Translation)


At the example above there are different addresses. For PC A, these address are:

Inside Local Address – 10.1.1.10
Inside Global Address – 55.1.1.1
Outside Global Address – 99.1.1.2
Outside Local Address – 99.1.1.2

Here the PC A ’s configured address, 10.1.1.10 is the inside global address. When this PC wants to go to the internet, it will use the Router A ‘s publica address, using PAT. So the inside global address of PC A is 55.1.1.1. Suring comunication with PC B, PC A access only PC B ‘s outside global address, 99.1.1.2.

If you fiinish this teorical boring part, then let’s continue with configurations;)

You can reach the other NAT articles below:
Network Address Translation (NAT) – Part 1
Network Address Translation (NAT) – Part 2 (Static NAT Configuration)
Network Address Translation (NAT) – Part 3 (Dynamic NAT Configuration)
Network Address Translation (NAT) – Part 4 (Port Address Translation)

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About the Author
Gokhan Kosem is a telecommunation and network engineer. His ambition to IP networks and end-to-end system installation made him to prepare this web-site. By sharing his experiences about various networking protocols beside different system installation experiences and Cisco, Juniper, Alcatel-Lucent devices configurations, he is aimed to be helpful for his collegues in all over the world. He is currently lives in Istanbul, Turkey.

5 comments for “NAT – Part 1 (Network Address Translation)”

1
SM

Hi Gokhan,

Do you have setup for these labs in packet tracer?
Also please provide your skype ID.

Thanks,
SM

November 12th, 2012 at 20:22
2
Junaid Jadoon

really a helping site but can i get video labs

January 4th, 2014 at 18:06
3
Faruq

Thanks for your helping.Its really useful.

January 24th, 2014 at 19:03
4
j boy

thank you so much , this is helping :)

March 10th, 2014 at 17:31
5
Mohamed Rafi

Hello Sir
Is this possible, can i configure NAT in SRS 6850E Alcatel switch.
How can i do the coding for VTP.

Thanks

September 1st, 2014 at 19:40

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