The next topic of discussion
is network address translation
network address. Translation is the process of
translating or converting
a private i P address to a public I P address.
Which brings us to what is a private I P address.
the International Engineering Task Force has described in the article RFC 1918 and R. C actually stands for request for comments and these air the original
Ah, that defined protocols and standards in, uh
in our networking community.
So oh, SPF has an artist. See, Rip has an RC,
so our C 1918 describes the ranges of addresses that are not allowed on the Internet.
So if you hit a service for lighter outer with a source address from the private address range, you'll either get a warning or because the service for a writer is going to think
that you are trying to do something. Militias. So these addresses are simply just not allowed on the Internet, and they're not globally row doble
companies. Private companies are allowed to use this address space within their environment. But if they tried to send traffic out to the public Internet, they need to translate to a public address.
Now these addresses are
the 10 range 10.0 through 10 to 55255255
or the 10 slash eight prefix.
Now, if you ever see address is written like this, do not get confused.
a lazier way off expressing the 10 Network.
So, for example, I have Let's see if I have a class less network 1 50
10 slash 21. I can detect defense this as 1 51 01
or so This being the I P address this being the network address, I can even shorten it further to 1 51 01 slash 21 leaving out the last two octaves because they're zeroes anyways. So if you ever see
and address depicted like that, just assumed the rest of the fields are zeros.
Now that's that. That's the Class A range. In the class B, you have the 1 70 to 16 0021 72 16 31.255255
with a slash 12 mask or the 1 72 got 16 slash 12 prefix
prefix just means the length of the mask or the network address, so the network address over here is 1 72 16
and then they have a Class C range, which goes from 1 90 to 1 68 00 through 1 90 to 1 68 to 55255 Last 16.
If I were you, I would memorize these addresses because on the test you might be asked to pick between private and public addresses.
And they usually get people by giving addresses close to the back end of the Class B range.
to do not we're going to do a lap soon.
But the easiest way I personally have seen or I personally memorized these issues. Just break it down
or the configuration. You break it down into four steps. Four simple steps.
let's say you work at a company and they're using private addresses, and now you need to go to the public Internet to do business,
and somebody gets assigned to go by public addresses. So the point I'm trying to make here is that you have to row purchase Ah, pool
off public address is now The pool could be 254 addresses, 50 addresses or maybe just one address
now the corner case of the pool being one address we'll explore
But the bottom line being initially when you want to go on the Internet and your your private firm needs to do business on the Internet or go through the Internet to another private company on the other side of the Internet. In another country,
you need to create a pool of public addresses on your outer.
You purchase these addresses
and let's say our pool when we do our lab,
let's make our pool.
Let's say we went and got the 1 90
That's a pretty big pool. It doesn't really work out like that in the real world, and we'll explore a really world scenario in a bit. But let's first understand how networks before we get into more complicated scenarios.
So this command is that I should stay on this side of the board, the commands in taxes.
I'd be not pool from CONFIG mode
and the pool name. Simply name the pool. We can call it C CNN.
Then you're assigned the first address. So from the 1 90 10 10 0 slash 24 range, the first address will simply be
Then the key word net mask
and then the summit.
And our subject mask in this case is
Well, now the first address. Sorry. 1 90 10 10 1 That goes here. Then the last address, which is 1 90 10 10 dot
254 dot to 55 being my broadcast.
So the last address goes here
Then the key word in that mask
and then the sub net mass, which will be 2552552550
After that, Step two is to permit your private address translation using an access control list.
So I actually have to allow Tell the router. Hey, allow these private addresses into translation. Allow them to get translated.
So for that, I simply use a standard access list
and I created using the I P access list standard and then give it a name command. We can call it Cisco.
you will always permit You're not going to deny, but the commands in text four Access control, this is comm permit or deny.
Forgot this little bracket here.
So you will permit, in this case, always
So let's say our private network is the 10 10 10 0 network.
So the network address will go here and then the wild card, which, if it's the last 24
then the next step Step three stewards simply tie step one and step here together
with the I've bean at inside source list. So it's basically asking if you read the command sent Texas asking, I mean, that I'm gonna do not using the inside source access list
inside source list. And our list was called.
I believe I called it. See CNN or no Cisco.
So the name, whatever name I put here in my access list goes here
And then the pooling,
which I believe we chose SEC. And
so our pool C CNN access list is
and then the keyword overload. We're gonna ignore this for now. As I said when we explore,
uh, Maur, um, real world scenario, we will look at this key word.
So for now, you'll just hit Enter,
then you have to go apply. You're not.
Let's just say you have a rounder
and you have f zero slash one on this side and F zero slash zero. Understand?
And let's say this and faces your domain. So this is
And let's say F 00 faces the Internet
or your service provider router,
so this would be your inside interface and this guy as your zero would be your outside interface.
by basically going inside each of these interface by saying interface in the face I D. So, for example, if I was going under
the inside into face, I would say I nt f zero slash one, in this case above.
And then I would simply say, I mean that inside on f zero slash one, and then I would go into ab zero slash zero and say I be not outside
now to check my work. Once traffic has passed through my translating router,
I would do the command or execute the command show I p Nat translations
and if for some reason I wanted to clear those translations out. My command would be clear. I mean act translations. Actually, there's a star after that. Clear I p Nat Translations star.
This concludes the lecture part, but let's go see how this works in the lab.