-: Network Address Translation.
Network Address Translation or NAT
is the process of changing an IP address
while it transits across a router.
Now in Network+, we discussed how this was used
because we wanted to conserve public IP addresses
because they were limited in IPv4.
In Security+, though,
we are going to gain an additional benefit when we use NAT,
we can actually hide our internal networks
from attackers.
Now, the most commonly used type of NAT
is what we call Port Address Translation or PAT.
This is where we have a single public IP address
assigned to a router
and all of the private IP addresses
that are assigned inside to our host.
In your small office, home office network,
this is most likely what you are using.
Now, when a host wants to communicate out over the WAN,
it's going to send the request to the router
and the router is then going to forward the request
out to the Internet,
to the server that it's trying to get to
on behalf of the host.
And when it does this,
it keeps track of the translation it does
by using a unique random high port number
for each request.
This means if the attacker is getting your network
from the outside,
they are only going to see that single public IP address
of the router
and they are not going to see the fact that you have
one, five, ten, or 100 hosts inside of your network,
and they are not going to be able to exactly know
how many devices there are
or what kind they are.
So, for the Security+ exam,
in addition to knowing about NAT and PAT,
you should remember
that there is public and private IP scopes.
Now, when you start talking about
private IP ranges,
you should have learned those
back in A+ and Network+.
If you didn't, I'm going to give you a quick review.
Class A is anything that starts with a 10,
so 10.0.0.0 all the way up through 10.255.255.255.
Now in class B, we have IP addresses that start with
172.16.0.0 all the way up through 172.31.0.0,
essentially, anything that starts with a 172.16
all the way up through 172.31.
Class C is really easy to remember as well,
and it's probably what you are using at home.
It's 192.168.0.0 all the way up to 192.168.255.255.
So, if it starts with a 192.168,
it is also a private IP address.
Remember, private IP addresses
cannot be transmitted over the Internet.
So instead, once they hit your external router,
it's going to use either PAT or NAT
to give it a public IP address and a port number
to send the information out to the Internet
and then receive it back.