The next topic of discussion is port address. Translation.
first tell you why or the need for port address translation before I tell you what it is
now, not all companies can afford to buy 254 addresses
if they have 254 employees in their internal network.
right now, our first I p was 1 90 10 10 1 and our last I p was 1 90 10 10 to 54
Which means? And I Internal network, supposedly we only have two hosts PC one NPC too. But
we're pretending that we have 254 people on our inside network. So our network was
slash 24 with a wild card being 000255
Which means for every person on my inside network
I had one public address
if they wanted to go out to the Internet.
Now these public addresses cost money
most of the time buying one address
per inside network to get translated to a public
address, it's not feasible Or nor is it cost effective.
So how do we save money. Well,
we make our first address
in the I P. Nat Pool pool name command,
the first address and the last address? The same.
Which means we shrink our pool down to one address on Lee.
If we shrink our pool down to just one address on Lee,
then we can do something called Nat with overload or poor address. Translation.
As you'll see, what will happen is multiple hosts
will multiple inside host with the 10 address in our case PC one in PC to
both of them to the same i p address when they go out.
Now you will ask me, How is that possible? How can two machines use the same I p address?
Well, the separation in the conversation or the data stream happens now at layer four.
So both PC one in PC to in this case, while doing that with Overload or Pat are going to use the same
source address off 1 90 10 10 1 So
10 10 10 1 and 10 10 10 to will bow to be translated the source address in the I P packets that these two host sent out
for both the host will be translated to 1 90 10 10 1
but they will be using different source TCP port numbers.
So the conversation now the separation and conversation happens at Layer four,
and the router will keep track of these conversations in. It's not Table,
so let's go ahead and see on our lab how this happens.