Time
15 hours 34 minutes
Difficulty
Intermediate
CEU/CPE
20

Video Description

Port Address Translation Now that you've learned NAT, we can explore Port Address Translation (PAT). We discuss at length the purpose for PATs, what their use empowers us to do and why. You'll learn the cost effectiveness of rather than purchasing one address for each network and why it's more management and cost effective to use the 1st address in the NAT pool and how the router tracks and manages this info in its NAT table. Once you grasp this concept you'll be able to understand how the Port Address Translation process executes.

Video Transcription

00:04
The next topic of discussion is port address. Translation.
00:09
Now, let me
00:11
first tell you why or the need for port address translation before I tell you what it is
00:18
now, not all companies can afford to buy 254 addresses
00:24
if they have 254 employees in their internal network.
00:29
So in our case
00:31
right now, our first I p was 1 90 10 10 1 and our last I p was 1 90 10 10 to 54
00:40
Which means? And I Internal network, supposedly we only have two hosts PC one NPC too. But
00:47
we're pretending that we have 254 people on our inside network. So our network was
00:53
10 10 10 0
00:56
slash 24 with a wild card being 000255
01:00
Which means for every person on my inside network
01:04
I had one public address
01:07
if they wanted to go out to the Internet.
01:11
Now these public addresses cost money
01:14
and
01:15
most of the time buying one address
01:19
per inside network to get translated to a public
01:23
address, it's not feasible Or nor is it cost effective.
01:27
So how do we save money. Well,
01:30
what if
01:34
we make our first address
01:37
in the I P. Nat Pool pool name command,
01:41
the first address and the last address? The same.
01:42
Which means we shrink our pool down to one address on Lee.
01:49
If we shrink our pool down to just one address on Lee,
01:56
then we can do something called Nat with overload or poor address. Translation.
02:04
As you'll see, what will happen is multiple hosts
02:08
will multiple inside host with the 10 address in our case PC one in PC to
02:15
will translate out
02:16
both of them to the same i p address when they go out.
02:22
Now you will ask me, How is that possible? How can two machines use the same I p address?
02:29
Well, the separation in the conversation or the data stream happens now at layer four.
02:35
So both PC one in PC to in this case, while doing that with Overload or Pat are going to use the same
02:43
source address off 1 90 10 10 1 So
02:46
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
02:58
for both the host will be translated to 1 90 10 10 1
03:02
but they will be using different source TCP port numbers.
03:08
So the conversation now the separation and conversation happens at Layer four,
03:15
and the router will keep track of these conversations in. It's not Table,
03:21
so let's go ahead and see on our lab how this happens.

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Cisco CCNA

Our free, online, self-paced CCNA training teaches students to install, configure, troubleshoot and operate LAN, WAN and dial access services for medium-sized networks. You'll also learn how to describe the operation of data networks.

Instructed By

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Junaid Memon
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