In the section we're going to discuss network address translation or not and port address translation
or pat.
We'll discuss why Knecht is required.
Why do we use net in networks today.
We'll also discuss the difference between Nat and Pat and we'll discuss the Cisco term overloading which
implies that a lot of network engineers talk about that even though they actually mean packed.
So we need to understand the differences between those two terms.
And as always I'd like to demonstrate how to set up Nat using the command line interface.
We'll look at different types of not including static not dynamic Nat and Pat or overloading as Cisco
call it before going any further.
Here's a demonstration.
I've disabled all network interface cards on my PC.
Except for the wireless interface card.
When I look at the details of that card I can see that my IP address is 1 9 2 1 6 8 1 89 and I'll have
a default gateway of 1 9 2 1 6 8 1 2 5 4 I can view that in a CMD prompt as an example.
So on my PC type IP config see the IP address see the default gateway.
I can ping Google dot com
so notice I'm getting replies from Google dot com.
I can access Google dot com.
So here's the Google web site.
But when I type what is my IP address into Google I'm told by Google that this is my public IP address.
IP config again shows me that my internal IP address or private IP address is 1 9 2 1 6 8 1 89.
But my public IP address is this.
So in this example my internet router at home is connected to the Internet and this route is configured
with DHP.
It's allocating IP addresses to devices internally using DHP.
And one of those IP addresses was allocated to my local PC but when I go onto the internet my address
used is a public IP address so a network address translation essentially translates a private IP address
which is non-radical on the Internet to publicly ratable IP address your public IP address is typically
allocated to you by your service provider which in my case is British Telecom or BT.
Here in the UK in large networks companies may register their own public IP addresses Yarrow's some
well known examples Hewlett-Packard own $15.00 flechette and 16 Apple own 17 MIT 18 forward 19 AT&T
32 and so on.
And IBM is an example nine dot sera sera sera.
So as an example if you working with HP or with an apple you may not be using a private IP address such
as this.
You may actually have a public IP address allocated to your PC.
These are globally readable public IP addresses that were registered by some of the largest companies
in the world but IP addresses are running out.
So in most small medium businesses today you'll be using a private IP address internally.