Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

NAT purpose

"Static NAT is known as one to one NAT, and is used to map a single IP address to a single registered IP address. It is often used for servers that need to be accessed via the internet" What is the really the major NAT purpose? To make a host be accessed from outside? Or for a host to access the outside world? If the answer is included the later case, why? Why can?t we just configure a host?s default gateway to a router and then the router will route the packet out to the outside world?


Re: NAT purpose

One of the main reasons NAT came into existence was IP address depletion. You would use NAT in conjunction with private (RFC1918) addresses which are not routable on the Internet. In such a case, your scenario of using a default gateway to a router etc does not work because the rest of the Internet cannot route back to it. You can use public addresses so that servers sitting in your network can still be accessed using a fewer number of public addresses than you would otherwise require.


New Member

Re: NAT purpose

Dear paresh,

Accordin to my concept on NAT, to secure the internal servers from outside world, we are doing NAT.

The main purpose of the NAT is to solve the shortage of addresses. But if we take Static NAT or Dynamic NAT we need the same number of Public ip addresses which is equalent to the configured local(private) addresses. Then Where Static or Dynamic NAT solves the problem of shortage of addreses.

Please clarify my doubt.

Thanks & Regards,


New Member

Re: NAT purpose

NAT solves the problem as you only need a Public IP for systems that need to be accessed from the outside world.

i.e if you have 100 users, and 3 servers, you only need 4 public IPs, one for NAT, and 3 for the servers. In this case the static NAT is used for the servers to ensure that they don't get given the wrong public address when packets are leaving, as this would confuse everything.

PAT, which is sometimes called NAT also solves the problem, as now you can use one IP to point to many servers, so long as they run services on different ports.

New Member

Re: NAT purpose

Static NAT = 1 private IP to 1 public IP

Dynamic NAT = 1 private IP to 1 Public IP (Need public IP Pool)

PAT (Packet Address Translation) or NAT overload = Many Private IP's to 1 Public IP

So the PAT is best for you if you have so many clients connected to your LAN using private IP's and you have only one Public IP.

Re: NAT purpose

Hi there,

NAT is not just used for hiding from the outside. I used to work for an outsourcing company and we used to take over management of many networks. A lot of the time these addresses would clash, so we had to use NAT to ensure no overlapping occured - not to hide.

Hope that helps,


Please rate all posts