Let's talk about sub netting so sub netting is important in networking you hear about it all the time
you hear even people perhaps freaking out.
I know I freaked out when I heard that I had to do it for exams like network plus or CCMA and I feel
like there are a lot of complicated methods out there for submitting but there was a method that was
shown to me middle of my career and it just blew my mind.
It's really really fast submitting method and I really want to break down for you what sub meeting is
why we do it and then show you the methodology behind it.
So if we want to talk about submitting if we just come in here and just do an eye f config and we look
at our IP address right we have our eye net which is our IP V4 and you can see here too we have this
net mask.
This is also known as a subnet mask or a subnet and it just says 2 5 5 5 5 2 5 5 0 doesn't really tell
us a lot if we don't know much about it but this is what a subnet looks like.
And we can think of subnets in ones and zeros it's all bits.
Right.
So we've got eight bits here.
Just like an IP address IP before same thing.
Eight bits eight bits eight bits and another eight bits and we've got ones and zeros if all the ones
are switched on we've got two hundred and fifty five.
If none of the ones are switched on we've got zero.
And depending on how those ones and zeros are switched on or off determines a lot of things for us and
that's why this net mass is important now.
Attached to your resources for this course I've created an excel sheet that I think will be useful.
So we look at the Excel sheet here is the cyber mentors submitting sheet and let's talk through this.
It looks like a bunch of numbers and it might look crazy for you.
And we're going to talk about how this breaks down how the bits break down and then how I would write
this shorthanded for an exam or a test or do something that I do on a day to day basis.
So first let's talk about the bit so come to the bits tab here and we have our 8 bits right wing countless
across and there's eight here on the count and you can see that and it starts with 128 and descends
down to one you just keep cutting it in half right.
So 128 64 32 sixteen eight whatever.
What's more important is why we get to these numbers.
So if we have a one switched on here it adds to the value when all the ones are switched on it equals
to 255.
You see all the ones switched on here if we were to highlight overall this come down to the sun you
see the sun is two fifty five.
That's all this formula is doing here.
So if we were to come through and you see all the zeros here nothing's flipped on to actually turn any
value on here.
How this actually works is the switch has to be on in order.
Right.
So if we were to switch on another bit we'd have to switch it on here and we'd have to switch another
one on here.
We could just come down here and switch it on here.
It wouldn't make sense it doesn't work that way.
Not with subnet.
So we're going to take these back off and show zeros again.
But you see how the values change if for example we had this network and you saw the default and I'm
showing you the 2 5 5 2 5 5 2 5 5 0 this standard here because that is what's known as a slash 24 network.
That's very very common and it's very common because it's used mostly in households and small businesses.
And it's done this way because of the amount of hosts that it allows.
Now if we talk about the host you can see that I have here two to the eight power why do I have that.
Well we actually go by how many bits are switched off our how many hosts are available to us.
So if a hosts here are a bit was switched on then we lose the amount of hosts we have available to us
and the subnet gets smaller and smaller.
Now don't worry too much about the ones and zeros.
It's gonna make a lot more sense when we stop talking in these binary terms.
I just kind of want to break down the math behind it first before we make it really really simplistic.
So again we've we're talking about what's called this slash twenty four whack twenty four network and
it's so standard because of the host.
Again 256.
Think of all the devices in your house you have cell phones you probably have computers you might have
like a Roku or Amazon Fire or something along those lines you may have smart TV's or smart watches or
something that connects to the Internet.
Well again they're all connecting through net right and going out but the amount of hosts that you can
have on your private network really depends on the subnet mask and how you set it.
So we have this class C that you saw before the 1 9 2 1 6 8 dot 1 or dot 0 or however you want to have
it.
Right.
Well it allows us to have two hundred and fifty six when we have a subset of slash 24.
So that's very common for a household it's also common for a small business maybe there's a printer
some few devices in there but they're never gonna get over this two hundred and fifty six hosts.
OK.
So when we come to the subnet cheat sheet let's break this down a little bit differently.
So we have our hosts here.
Let's start with the slash 24 we just were.
And you saw that there is 256 available hosts as we start turning off bits OK.
We turn off a bit here we turn off a bit.
Keep going down the list.
The host start getting bigger and that just corresponds.
Here we have a slash 24.
And the only reason I'm saying twenty four is I'm counting the ones across.
Right.
So we've got 24 bits switched on.
If we had twenty three OK.
It gets bigger and bigger and bigger.
Now let's stay away from the ones and zeros.
I think it's a little bit complicated.
The better way to think about this is to look at the subnet mask down here and I'm going to replicate
this.
And then we're going to come back to it.
So what I do here is we can have a possibility of 32 bits switched on.
Right.
So I'm just making a new tab and I'm just gonna go over here and I'm going to hit control and drag this
across till it hits eight OK.
And then I'm gonna do the same thing with nine on the drag and across all I'm doing is just making really
quickly 30 to place holders and I'm just emulating here.
If we had the possibility of thirty two different switched on bids.
So imagine one bit of switched on.
Imagine all 32 bits are switched on.
That's the possibilities here.
Right.
So always for sure we're going to have an amount of host and we're gonna have a subnet mask.
OK.
So we'll just call it subnet their we always start here with 128.
Just like the bits that you saw.
You saw the 128 start in the bits.
Let's just start also with 128.
Now as you saw every bit that switched on.
Remember when we switch a bit on over here it starts decreasing.
So we're gonna decrease for the bits that are switched on.
Sixty four thirty two 16 8 4 2 1.
You come over here and when I like to actually do is I like to just add these numbers together and you
could see one twenty and sixty four is one ninety two and then you can add these two together so you
get one ninety two thirty two you just add diagonally is the way I've I actually always do it.
So two twenty four to forty to forty eight to fifty two to fifty four and two fifty five.
Now what does that correspond to.
It corresponds to the possibilities of the bits being flipped on right.
So this looks just like what you see here.
Same deal.
And if you had a one underneath of it.
OK.
Then you got 128 if you've got another one underneath of it.
Well guess what.
You've got one twenty eight plus sixty four which is one ninety two and this number keeps growing.
Why is this important.
This is still all ones and zeros right.
Well let's start thinking about it.
If we have a slash twenty four network we've got twenty four bits turn on our subnet mask is 2 5 5 2
5 5 2 5 5 0.
If we had a slash 16 it becomes 2 5 5 2 5 5 that 0 0.
Why.
Where are these changes coming from.
Let me show you this.
OK for a slash a.
I'm just tying this into just this right here.
Well this is coming from the number of bits that are turned on eight bits turned on.
We've got 2 5 5 and the rest are zeros.
You got another eight bits turned on 2 5 5 2 5 5.
The rest are zeros come down to this slash twenty four which is that really common subnet that you see
and you've got 2 5 5 2 5 5 2 5 5 0.
Now this is very common.
OK.
And let's go back to the cheat sheet now and you could see that I've got X as a place holder in the
subnet.
So what I'm saying here is you look at this list and you say I've got a slash one well for this whole
area here from one to eight the place holder is going to hold in place of this X..
So for a slash one if I've got one 28 then guess what it's going to become 1 28 0 0 0 because that's
how it would be if you turned on just one bit here and made all of these zeros.
Guess what.
Just the 128 would be on the rest would be zeros.
OK.
If we had a slash 14.
OK.
So two five fives automatically flipped on you have a slash eight already you pass through it.
OK.
So you're starting on the second iteration here slash 14 corresponds down here to 252.
So you'd have a 2 5 5 2 5 2 0 0.
So all this is is place holders let's go back to the sheet here.
So I make this quick and dirty list.
This is what I write out when I'm just writing out something quick for an exam.
All right out one thirty two I'll put the host here and I'll put the subnet here.
So again if we know that once we cross through eight 16 24 32 that has a two five five in front of it
all we've got to do then is we'll say slash twenty seven.
Well we've come through three columns then I know for sure that we've got 255 255 255 got something
right.
You see the slash twenty seven.
You come down here.
The subnet would be to twenty four say 28.
OK.
2 5 5 2 5 5 2 5 5.
Look at the 28.
You've got a dot 240 and this is going to be confusing.
This is subnet it is not necessarily easy once you get the chart down it makes a lot more sense.
So let's start piecing some more things together.
When I say that I've got host now the host I'm showing you only correspond to these first two rows but
it's very common or very useful just to know this number right off the bat.
Now if you look at the cheat sheet what you can do here is you just know that you start with a one or
you start with the 128.
You go down but every time you go up your doubling and why are we doubling do remember from the bits
part every time a bit is turned off.
So as we go up a number we take it to the next power.
So we've got ape it's turned off.
We take two to eight power.
It's 256.
Well here you go.
Look come through here.
Two fifty six.
We go to the ninth power 512 to the tenth power.
Ten twenty four.
It just keeps doubling.
OK.
That's all you've got to think about in your mind is he keeps doubling.
So on an exam for example you might have something like what.
How many host could be potentially in a slash 20 network.
And you come to your cheat sheet that you made or you have in your head and you say well four hundred
ninety six and then we'll get to this in a minute but we have to subtract two.
So four ninety four potential.
And why is this all important.
Why do we even care about any of this.
Why am I rambling on.
Well you need to know based on the network.
OK.
The slash twenty four is great for a small office home network.
However you want to have it.
But what if you're a large enterprise.
Maybe you have thousands of devices.
OK maybe you want to slash 16 network.
That might make more sense for you or you even see some with a slash 8 network.
It just depends on how big the company is the larger the company the greater chance that you're going
to see that they're not using slash 24.
Or they could even have submitted segments of their network where say they have just telephones and
they've got five hundred employees and five hundred telephones.
They might just have one slash twenty three network for nothing but telephones because that's the amount
of hosts that fit in there.
So what we're after with submitting is how many hosts can we fit and what is the mask that's behind
it.
So those are questions you might be asked in exam.
And these are questions that you're just going to see and when you're given addresses see you're doing
a pen test for a client.
You might be given something like this.
You might be given IP address 1 9 2 1 6 8 1 0 0 slash 24.
OK.
And immediately in your head you're like oh slash 20 for that standard.
There could be up to two hundred and fifty six hosts or 250 for hosts or devices in this network.
But if they gave you something like 1 9 2 1 6 8 1 8 0 0 slash 20 then you might look at your little
chart and say four thousand ninety four hosts.
Remember when you subtract two four thousand ninety four hosts in this network.
Now I know if I'm scanning this I'm up against a lot more devices potentially than I am in this.
OK.
So when a client gives you your subnets they might just write it out like this.
And depending how big your client is might depend on how big their subnets are for you.
For example I just pen tested a client that was a slash 16 all the way across and it looks something
like 10 dot 1 0 0 slash 16.
OK.
And your subnet mask for that would be something like 2 5 5 2 5 5 0 0.
And how does this come into play.
Well every time you have a two 5 five that number is locked in place.
That's another way to think about this.
So that 10 is always locked down.
This one is always locked down the rest of the bits are fair game meaning we could have 10 dot 1 dot
1 0 dot one die two to three we could actually have a zero here zero not one got to the three to four
and that's how this number like a slash 16 gets so big because you have ten got one dot zero zero through
two hundred fifty five on the possibilities which equals two hundred and fifty six hosts.
Ok for one range you get 256.
Well imagine you have to do that two hundred and fifty five other times.
Right.
And that number gets substantially bigger here.
And then if you were to have a slash eight then of course it gets bigger and bigger.
So what you need to realize are a few things here.
We have these addresses and you see the slash ones.
I say again we call them wax whack 24 is going to be very common.
I would say whack 16 is probably your next common you might see some weird sub minted networks like
this subnet networks like this.
But typically it's slash 24 slash 16.
Now your network I.D. is typically what is known as your first address and your broadcast diary I.D.
is known as your last address.
This is not always the case but it is very common.
And let me log back into this Kallie machine here and I'll show you.
So we have our IP address 1 9 2 1 6 8 fifty seven dot one thirty nine.
And we've got a net mask of 255 255 255 0.
What does that tell you from what we just learn that tells you we have a slash 24 network.
OK.
This is a common network.
There are potentially two hundred and fifty four hosts.
Why do I keep saying.
Why do I keep subtracting two.
Well we've got a network I.D. and a broadcast I.D. or broadcast IP here.
Well what we need to know is we are dot one thirty nine.
We could be anywhere from one to dot 254 within this network.
That's our two hundred and fifty four possibilities.
This zero means we have the flexibility to be any IP address range from one to two hundred and fifty
war usually usually a dot 0 for this IP here in a dot two fifty five.
Make up your network I.D. and your broadcast IP.
OK usually so if we were to say something along the lines of let's go back to this Excel document and
we were to say something along the lines of this let's say that we have a slash 24 network and we want
to know how many host We want to know how what our network ideas and what our broadcast ideas for IP
is.
OK.
We would say OK and we'll we'll get it one more.
We'll say it's a slash 24.
And the IP starts with 1 9 2 1 6 8 dot one dot zero.
OK.
Or we can even write it like this.
1 2 1 6 a 1.0 slash 24.
Delete this and we'll say what's our subnet mask.
What's our host what's our network what's our broadcast.
So subnet you come to your cheat sheet you say OK slash twenty four.
I already know that I need to be filling in this area here on the X so I'm just in come in 255 255.
What's the x.
Well we know to come down this row to fifty five here.
God zero.
Okay.
And then we've got host somebody can expand this a little bit.
We've got the hosts OK.
Hosts are right here 256 hosts potentially 254 though because we always subtract two from the hosts
total.
So our network I.D. is usually the first address available to us which is 1 9 2 1 6 8 1 0.
The broadcast is 1 9 2 1 6 8 1 255 meaning available to us is anything from DOT 1 2 dot 254.
Let's take a look at something else.
That's a basic example.
Let's do like a slash 28.
Let's say we got 1 9 2 1 6 8 1.
Got zero slash 28.
Now what.
Well you've got 16 hosts here.
OK.
So our subnet is then going to fill in 2 5 5 2 5 5 2 5 5 x.
Right.
Because we're in this row slash 28 says it's gonna be a 240 when we drop down to the subnet mask.
I'm going to make this a little bigger how many host sixteen minus two.
We have 14 hosts.
Okay.
So the first non host would be a 1 9 2 1 6 8 1 0.
Again still the same thing first first address.
Last address is going to be what.
1 2 1 6 8 1 15.
So it makes sense zero to 15 is sixteen addresses usable space is 14.
Because we take out the network and the broadcast.
Now you could see something like this and then guess what you're segmented so because you're only using
this little bit of space you can then in turn have something like this 1 9 2 1 6 8 1 16 slash 28 and
then it starts the same way your subnet mask is actually the same because you're using a slash 28 you
come through.
You can just copy and paste that.
The hosts are still the same.
What changes here well your first address 1 2 1 6 8.
Got one.
16 and then your last address which is 1 9 2 1 6 8 1.
That thirty one.
So because this is smaller on the slash 28 side we can actually have multiple networks within like say
a dot 1 0 dot one dot sixteen dot one dot thirty two.
You get a multiple little networks here with only a small amount of hosts so maybe you have just a few
servers in this range and you have like servers a b and c they go in a slash 28 and then you have another
one of servers DC in your DB D E and F however you want to say it and you have more in that range case
you can subnet this out into different things and we see subnets we see all kinds of stuff we could
see phone servers user computers wireless all different sort of thing some companies get really specific
with their subnet.
Now let's try one more.
Let's say we have a slash twenty three.
Now I want to put in 1 9 2 1 6 8 1 dot 0 slash twenty three but that would be wrong.
Why would this be wrong.
This is actually going to be a zero and I'll show you why in a second.
So we're no longer locking in the this this number anymore right.
When we get below the slash twenty for the two fifty five all the way across for three of them.
Guess what we're now have the ability to change is no other than what's locked in.
So let's do adopt zero.
We'll talk about why it's hit enter here.
So the subnet on a slash.
Twenty three.
Well we're gonna do a two fifty four which is going to be a place holder of the X here to come in and
say 2 5 5 2 5 5 2 5 4 0.
And now again we're not locked in.
So remember this two fifty five would lock in this dot one that doesn't happen anymore.
So we've got two fifty five to fifty five 254 dot zero.
We're actually going to start at zero here and we're gonna say the number of hosts that are possible
it's five 10 five twelve minus two will say our network idea is 1 9 2 1 6 8 0 0 and our broadcast would
then be 1 9 2 1 6 8 got 1 2 fifty five why.
OK so we have the possibility now that we're spanning two ranges we've got five hundred and ten hosts
in this network.
And we have the ability to go between zero and one we've got two options now zero and one.
So if we were to say another network if we wanted to get to like two we'd actually have to say 1 9 2
1 6 8 2 2 0 slash twenty three it would be the same subnet mask same number of hosts but then this would
be 1 9 2 1 6 8 8 2 0 1 9 2 1 6 8 3 2 fifty five.
Again there's five hundred five hundred ten possible hosts in between this.
Right.
Because you've got to think dot 0 dot 1 0 9 2 0 3 all the way through 254 and again one dot one one
dot two all the way through 254.
So that equals five hundred and ten.
Once you've hit that maximum that one dot 255 five then guess what.
You start to.
You have a whole new network here just like these smaller segments you get whole new networks on the
bigger side as well.
So what you need to know is that when I if I would put something like a 1 9 2 1 6 8 dot 1.0 slash twenty
three that would have fallen into line with the one in the zero in our actual network ideas still would
have been 0 0 and a one dot 255 would have been the broadcast here and you can double check this anytime
you're confused you can double check your site or notation.
So I'm going to bring over a Web site that I will show you here and this is just an IP addressing guys
called IP address guide dot com.
You bring this over and you scroll down just a little bit and I just put in 1 9 2 1 6 8 1 0 slash twenty
three and you can see that it actually corrects me and says the first bit is 1 9 2 1 6 8 0 0 0.
The last ones 1 9 2 1 6 8 1 255 total hosts is 512 minus two shows you that again first ip last IP you
got your net mask.
Very easy to use a cyber calculator here or an IP range to convert decider as well.
So very useful calculators.
But if you're not allowed to use these for like an exam purpose or something along those lines then
using the cheat sheet that I've shown you is super useful.
Now what I want to do is I want to try for three more subnets.
I'm going to write these out.
I must say 1 9 2 1 6 8 0 0 slash 20 to 1 9 2 1 6 8 1 one zero slash twenty six and 1 9 2 1 6 a dot 1
0 slash 27.
I want you to solve these for me.
Tell me the subnet mask the host network and broadcast it with that being said this again is a very
complicated topic.
I did not pick this up the first time or the second time that I got it.
If you're running confused right now perfectly normal you can go back and watch this video again try
to pick up more topics try to understand it maybe I'm not the right instructor for this either I do
recommend looking at other resources to completely fill in your knowledge gap if there is one that exists.
Another resource that I'll link down is what is called Seven second subheading it is very useful a lot
of students have recommended it to me.
I'm going to push it forward as well.
So go ahead and try to solve this.
Understand that what you're after here is just understanding what a subnet is.
OK.
When you see something like this if a client sends you 1 9 2 1 6 8 1 0 slash 24 you're going to say
hey OK I know that there's probably 250 for hosting that network and I know what I'm working with.
If you see this 2 5 5 2 5 5 about 2 5 5 0 again you know that you're working with a slash 24 network
very standard stuff.
That's what we're after.
I don't expect you to ever memorize this.
I don't have this memorized like I don't come in here and say you know a slash 18 is a 2 5 5 2 5 5 1
9 2 0 network and it's got sixteen thousand three hundred eighty four hosts I don't do that.
OK.
I have a cheat sheet I'll use a Web site if I need to for the most part what you need to understand
is to 250 for hosts for a slash twenty four if that number has gone up to like a slash twenty eight
you know you're dealing with less if that number is lower like a slash sixteen you know you're doing
with a bigger network that's really what it comes down to unless you are working in networking and then
these become more important but as a pen tester understanding how to read this understanding what the
subnet is and just identifying it with very basic measures this is extremely useful so I'll get you
over in the next video when we talk about solving these challenges and hopefully we got them all right
so I'll see you over there in the next one.