In this video,
I'm going to show you how to do subnetting by hand.
This way we can eliminate all of the math
and all of the pen and paper
and be able to get the answers we need really quickly.
It's really just a shortcut.
In the last couple of videos,
I showed you how everything worked
so that you understand the theory behind it all.
But now we're going to get to the quick way of doing it.
So when I subnet by hand to do this demonstration,
I'm going to wear my subnetting gloves.
Now, my subnetting gloves are special
because I have little numbers written on the backside of 'em
that I'm going to show you here.
So you may see here on my subnetting gloves
that I have numbers written on them.
Now, in the real world,
you're not going to have your gloves on,
but you can memorize these numbers fairly easily.
They're just power of 2.
Now, if I'm going to start on my right,
which on your screen is going to look like the left,
you'll see I have 2, 4, 8, 16, 32, 64, 128,
and 256 written down.
This tells me how many networks there are.
This goes back to our 2 to the nth power,
which was our formula that we used when we did this by hand.
So if I asked you if you had a /26 network,
how many subnets can be put into a /26
if you were given a /24 to start with?
Well, if I have a /24 to start with,
I'm going to start counting up from there.
So my first finger is going to be /25 and then /26.
Since I asked for a /26,
you can see the number is four.
Now we can do it the other way
and we can go from my left to right,
but in your case,
it's going to be your right side of the screen to your left,
and this is going to tell me how many hosts or IPs I can have
inside of a network.
So if I start from the other side
and I start with a /24, I have 256,
/25, I have 128, I have a /26, that's 64,
/27, that's 32, /28, that's 16,
/29, that's eight, /30, that's four,
/31, that's two.
So you can see how this works,
going from right to left or left to right
be able to figure out how many networks
or how many IPs are available.
Now we're going to do a couple of examples using this method.
The first one I'm going to use is this one,
it's 192.168.0.85.
Now, the numbers really don't matter.
It's really what's important is that /29 at the end.
So if you wanted to figure out
how many subnets there were in a /29, how would you do that?
Well, we're going to count up from right to left,
upwards in the power of 2.
So if I start counting on my fingers,
I go 25, 26, 27, 28, 29.
And what's on my 29?
It's 32.
There are 32 subnets if I'm using a /29 network
within a normal Class C network.
Now, if I'm going to look at this from an IP perspective,
I'm going to do it the other way.
How many IPs are there in a /29?
Well, we're going to start with /24, 256,
/25, 26, 27, 28, 29.
And there you'll see I have eight IPs.
Now, if you remember from our lessons,
you always have a broadcast
and you always have a network name.
So really, I have six usable IPs for hosts.
I have the first IP, which is my network,
and my last IP, which is my broadcast,
giving us a total of eight.
Again, that's at /29, that's eight.
The next problem we have is 192.168.1.25/28.
So if I'm doing /28, how many subnets and how many IPs?
Well, let's pull out our gloves again and we'll start.
We have /25, /26, /27, /28, and the /28 has 16 on it.
Now, if I go the other way for how many IPs,
I'm going to go /24, /25, /26, /27, /28.
It's also 16. So we have 16 subnets and 16 available IPs.
You can see how this works. It makes it really easy.
So I think you're getting the idea here,
but let's try two more.
This next one has a /30.
So how many subnets and how many IPs?
Well, let's pull out our gloves again.
And so we have /25, /26, /27, 28, 29, and 30.
And on 30, you see 64
because we count it up 2, 4, 8, 16, 32, 64.
And so by doing that, we now know we have 64 subnets.
That's what a /30 is.
I could take 256 IPs in a Class C
and I could break it up 64 different times.
Now how many IPs is that going to be?
Well, it's 256 divided by 64,
but if we use our gloves, we can go the other way,
24, 25, 26, 27, 28, 29, 30, and it's four, four IPs.
Because if we have four IPs and 64 subnets,
that's going to give us 256 total.
Let's try another one. This one's going to be a /31.
Now a /31, that's not even on the table
you told me to memorize, Jason.
That's right.
That's because it's a non-standard one,
but Cisco does support it.
It's usually used for point-to-point connections.
So if I'm going to connect one router to another router
and I don't need to have a network
and a broadcast in that case with Cisco devices,
I can use a /31.
So I'll only use two IPs instead of the four that we had
in the last /30 example,
which is normally used for point-to-point.
But again, if we pull out our hands,
we can start going and figuring out how many subnets
and how many IPs.
So let's do that /25, 26, 27, 28, 29, 30, 31.
So that tells me it's on my seventh finger.
So if I didn't have my gloves on,
I would just do powers of 2, 2, 4, 8, 16, 32 64, 128.
And so that seventh finger is 128, there's 128 subnets.
Now, I'm sure you can do the math here.
If there's 256 total IPs in a Class C
and we just took up 128 subnets,
that means there's going to be two IPs per subnet.
So let's do it with our hands anyway,
just because that's what we're doing in this video.
And so here we go.
We're going to go 24, 25, 26, 27, 28, 29, 30, and 31.
And on 31, we have a two, right?
We can do that if we went and counted up or counted down,
256, 128, 64, 32, 16, 8, 4, and 2.
And that gets us to that same number of two.
So it's all about memorizing these power of 2
as we go through this.
Again, a /31 is something that Cisco supported.
Some of the other routers are starting to support it,
but it is something that is mainly a Cisco thing.
Let's go ahead and do one last one here,
and this one is going to be a /32.
So when we're doing a /32,
you may go, "Do I even need to use my hands?"
Well, you really don't
because a /32 just denotes a single host.
If I have your IP address and put /32,
it means it's only that IP.
And so that really is just one IP
and there can be 256 subnets.
But if you want to use your hands, you can do that, right?
Because we have 25, 26, 27, 28, 29, 30, 31, and 32.
And you see on 32, it's 256. I think you get the idea here.
So this is how you can do this
in a very quick and easy manner.
Now, before we finish this video,
I do want to put this to practice
to some of the things you're going to see
on the Network+ exam
because you're likely not going to get a question
that just says how many subnets or how many IPs.
It's going to be a little bit more complicated than that.
So let's go to the next question
and you're going to be able to see what we have.
So in this case, I have 171.129.67.160/25.
And the question I have for you is, what's the network IP?
What's the first host?
What's the last host? And what's the broadcast?
So let's pull out our gloves and take a look at this.
So if I pull out my gloves
and I go for the first one, a /25 is two subnets.
Now with two subnets,
that means if I'm using 256 IPs,
remember I told you on the Network+ exam,
we're always going to assume that we're doing this
in terms of a /24 or greater
because that's usually what you're going to see on the exam.
So in this case, we're going to start with /24 is 256 IPs.
Because this is a /25, I'm going to have two subnets.
So I take that 256 and I break it in half, right?
So if I have two subnets, what's the first subnet going to be?
Well, it's going to start .0.
What's the second subnet going to be?
It's going to start at 128 because we have 128 IPs.
So the first one goes from 0 to 127,
and the second one is going to go from 128 to 255,
which gives us our network ID.
Our network ID is 171.129.67.128,
and our broadcast ID is going to be .255.
So what's our first host and our last host?
Well, it's going to be .129,
and our last host is going to be .254
because our first host is always one above
what the network was,
and our last host is always one below
what the broadcast was.
That's how this works when you're just doing it
with your hands, it makes it very quick and easy.
Let's try another one.
The next one we have is 56.187.210.21/28.
So if I want to take a /28,
we want to ask how many subnets and how many IP addresses
'cause that's going to help us write down
where our network and broadcasts are,
and that helps us figure out our first hosts
and our last host.
So if we have a /28, we'll pull out our gloves
and we'll go 25, 26, 27, 28,
and 28 is my pinky, which is a 16.
So there are 16 subnets.
Now if I go the other way, how many IPs are there?
Well, 24, 25, 26, 27, 28.
There's also 16 IPs. So 16 IPs and 16 subnets.
Now if you take those 16 IPs,
you're going to go 0 through 15, that's the first range,
16 through 31, that's the second range.
If we look at our IP address we were given,
it ended in .21.
Where does that fall?
Well, it falls in that second range, from 16 to 31.
So our network is 56.187.210.16,
our broadcast is 56.187.210.31,
and then we take our last host,
which is one less than the broadcast, .30,
and our first host, one more than the network, .17.
That's how we can do this all just using our hands
with no pen and paper,
we can get these answers very quickly as we go through.
I hope this subnetting by hand was helpful.
And if you didn't get the first time,
go ahead and rewatch the video again
'cause once it clicks,
it makes all of your subnetting problems so easy
and so quick to get through
and you'll have no issues on the Network+ exam.