- Okay, next on the list, let's talk about subnet masks.
The subnet mask is something you're gonna use
in conjunction with an IP address.
and we'll use IPv4 addresses for our example.
So let's say we have an IP address at 192.168.1.100,
just as an example.
That's our IPv4 32 bit IP address.
The subnet mask, and I'll just label that as SM, for this
will normally be 255.255.255.0.
And this tells us two things,
the network portion of our IP address
and the host portion of our IP address.
So if we take a look at the triple 255
and we line that up, we'll see that that equals 192.168.1.
It corresponds to that, I should say.
Every 255 together creates the network portion
of the address.
So the network that the computer is on is 192.168.1.
Then you have that last octet, that zero.
If you see a zero, then that deals with the host portion.
And in this case, the host portion is gonna be 100.
Other classes of IP networks
will use different subnet masks.
This is a class C address.
In a class B network,
such as say 172.16.1.1, just for example,
you might have a subnet mask that is 255.255.0.0.
So once again, the 255s indicate the network portion.
So 172.16 is the network that you're on.
And then 0.0 is the host portion.
So .1.1 is gonna be the post portion of the IP address.
And so that's a class B example.
Rounding it out, the biggest networks,
enterprise networks, government networks, they use class A.
An example of that might be 10.0.0.1.
And the typical subnet mask for a class A address
or a class A network would be 255.0.0.0.
And you can see the pattern here.
So in a class A network the 10 is the network number.
And you can see that is indicated by the 255.
The zeros indicate the host number, 0.0.1.
You can have lots and lots of IP addresses,
16 million in the class A 10 network.
So again, this is class A, this is class B,
and this is class C.
This is all in what's known as classful IP addressing,
which you may or may not use.
You might use CIDR or another type of concept,
which we'll cover later.
So keep that in mind.
You might have classless, but in this case
we're talking about classful IP addressing, classful.
So we have our class A, class B, and class C.
And it's that subnet mask
that defines what portion of the IP address
is the network portion and what portion is the host portion.
And that's it for the sub lesson.