### CompTIA Network+

Course
Time
60 hours 39 minutes
Difficulty
Beginner
CEU/CPE
61

### Video Description

Classless Inter Domain Routing (CIDR) This lesson discusses Classless Inter Domain Routing (CIDR). CIDR allows us to have variable-length subnet masks. Subnet masks within CIDR are not within the standard classes of A,B or C and CIDR notation is used when standard subnet masks do not work and allows us to break up subnet masks and work with IP addresses.

### Video Transcription

00:04
So our next top next topic that we have to discuss is something called Cider Now cider. It's not something that we drink in networking, but it stands for classless inter domain routing. C i. D e r.
00:16
Now we talked about class full routing with class full routing. We have class A Class B and classy I P addresses and there some that masks are default for those particular I P addresses. So in class, full route I p addressing
00:34
any I P addresses, which are in the Class A range, have the sub net mask of 2 55.0 dot 0.0
00:41
in the I P addresses in the Class B range have the I. P address of 2 55 to 55 0.0, and any I P addresses in our Class C range have the address of 2 55 to 55 to 55 0
00:54
Now there's another topic that we need to discuss again called cider, and what this does is it allows us to have variable lengths of net masks. So when we're using cider, it means that we have sub net masks which aren't in those standard classes now. This will come in especially useful when we're talking about sub netting and a little bit.
01:14
But
01:15
cider notation is seen as a slash and then a number, and that number corresponds with a sub net mass.
01:23
Now
01:26
why do we use cider notation? Well, we use cider notation because sometimes our standards sub net masks aren't going toe work for us. We need to have some way of breaking our sub. Are breaking our I P addresses. Breaking up our network ranges into smaller sub nets
01:42
and we can't do the We can't do that with our standards. Seven. It masks with our standard class full addressing.
01:49
Now it's important to keep in mind that we need to understand the limitations of certain devices on our networks, such as routers, to understand if they can do this classless. Addressing
02:00
most of our com, most of our modern devices on our network we're going to see today are able to do this, but classless addressing allows us to break up our seven masks and work with our I P addresses so we can make the most use out of them. We talked about how our class a There's a large
02:19
difference between our class A Class B and classy networks
02:23
as far as how many networks versus how many hosts there could be on each network. And sometimes we need to be able to adjust that. And that's where cider comes in.
02:31
Now
02:32
we display cider as
02:36
a slash, followed by a number.
02:38
Now this number can be anything from 1 to 31.
02:43
So what does this number mean? Well, this number
02:46
the slash in,
02:49
is our prefix.
02:51
Now, what we mean by prefix is when we break our sub net mask into individual bits.
02:58
That number is the number of those bits starting from left to right that are ones.
03:06
Now, when we're talking about our sub net, masks are sub net. Masks have to be continuous. Ones are continuous ones from left to right. We can't have a break with zeros in it, and we can't go from right to left. Our sub net masks have to go
03:22
left to right, and there can be no, there cannot be zeroes in between one's. It just has to be straight ones until we stop.
03:29
So our sub net mask of slash 16 would mean that we have 16 in a row, straight ones.
03:38
So let's take a look at that in our binary. Now we know from our earlier lessons that an I. P address an I P Version four address is a 32 bit address, which means it has 32 ones or zeroes.
03:52
Those 32 ones, or zeroes, are broken into four groups of eight, called octet. It's four times eight equals 32
04:00
and those octet make up the numbers and our I P addresses or our sub net masks.
04:05
So we have our
04:09
Dash 16 here
04:11
shown as 11111111.11111111
04:17
That's 16 straight ones. Now. Just because we have a slash 16 doesn't mean we can excuse are dots in between our OC tests, we don't write 16 straight ones and then a dot we still have to break up in tow ock tents. So we have eight ones and then
04:34
continue on with eight more ones and eight plus eight is 16. That's how we get our slash 16.
04:41
So we've talked about how we translate binary into our numbers before, but how do we translate this buyin ery again into our sub net mask
04:50
via standard numbers? Well, let's take a look.
04:55
So we drew out. Are buying. They're here
04:58
are 16 one's followed by 16 zeros because we have slashed 16 in the slash 16 refers to our 16 ones. They go left to right,
05:08
and we also drew out our chart.
05:10
Now, this chart corresponds which Egypt, With each of our OC tents, we've talked about how binary increments Bye bye. Increasing powers of
05:19
of two starting with 01248 16 32 64 1 28
05:28
Because a binary digit can either be can only be a one or a zero corresponding with an electrical signal of an on a one or off zero
05:36
and our computers at the very base language talk and electrical signals on and offs. So we have to translate those two. We have two trains like those two numbers so we can write applications and develop programs that can talk down to that.
05:50
So
05:53
how do we translate these ones and zeros into standard numbers? Well, again, we draw our chart
06:00
and we line up our chart with our octet
06:04
So we have our first octet here, and I can tell you right now that if you ever see an octet, that is all ones.
06:12
That octet is 2 55
06:15
An octet with all zeros is zero.
06:18
But let's actually take this and dissected out in order to understand why an octet with all one's is 2 55
06:27
So
06:28
we have our chart, and in our first place, our first place indicates whether it's a value of zero or one. But again, our sudden it masks we're gonna go from left to right. First place will indicate a zero or one
06:42
a zero or 20 or 408 You get the idea 16 30 to 64 1 28
06:49
if you're doing if you're doing an exam, you're taking a test. Or maybe you're just trying to learn some netting better. It's, uh, it's a good idea to have this chart already written out for you. It's good if you can get like a little white board so that you don't have to constantly be erasing and scribbling out pencil or rewriting the chart and pen
07:09
and just get your white board and practice this over and over and over in order to
07:13
become very familiar with these numbers.
07:15
So we have our chart here, and we have all ones. So
07:19
we fill out
07:21
our chart
07:24
with our eight once
07:30
now in binary or when we're doing our I P addresses and we're translating from binary to our standard numbers. We now take every place that has one in it
07:42
07:44
So we end up, we end up having 1 28
07:48
1 28 plus 64 which is going to give us 1 92
07:54
Then our 1 92 versus 32 which is going to give us our 2 24
08:00
to 24 plus 16 is going to give us 2 40
08:03
to 40 plus eight is to 48.
08:07
2 48 plus four is going to be 2 50
08:13
two fifty's
08:15
2 52 Sorry, that took longer than it should have.
08:18
2 52 plus two is going to be our 2 54
08:22
and 2 54 plus one is going to give us our 2 55
08:26
That's why our standard sub net masks the highest number that they can be and also in i p. Addressing the highest number a single octet can be is to 55. Because if all of those ones in the octet,
08:41
or if all of the bits in the octet are ones, the highest number that can add up to is to 55.
08:48
So
08:50
we have our 2 55
08:52
and then our second place again is all one. So it's also 2 55
08:58
So this
09:01
dash 16 is just 2 55.2 55.0 if it was a class be addressed, this would be it standard sub net mask.
09:09
So
09:11
this was an easy one. This was an easy one to get started. If we see a dad, if we see our cider notation in dash increments of eight, then we know that because it's in an increment of eight, we're just going up the chain and adding additional 2 55
09:28
So, for example,
09:33
a Dash 16
09:35
would be equivalent to a 2 55 to 55 0.0.
09:41
A Dash eight
09:41
would only use this first octet and then have the rest zeros, so that would just be to 55.0 dot zero
09:50
not zero,
09:52
and then a dash 24
09:56
would be to 55 to 55.2 55.0.
10:03
Now, we can't have a Dash 32 because as our sub net mask, because that's not gonna leave us any room for hosts. A Dash 32 would be to 55 to 55 to 55 to 55. And that would mean that our entire I p addresses the network I d. Thus giving us no room for hosts. So we're not going to see a Dash 32
10:22
cider notation for sub net mask.
10:26
Now those air easy. Those increments of eight are easy,
10:30
but they're a good place to get started at to understand how cider notation works. Let's do one that's a little bit more tricky. Let's take a look at Dash 12
10:39
so I have question marks there because we don't want to make it too easy for everybody.
10:43
So let's go ahead and a race. Our chart here,
10:48
our race, our chart right here
10:52
and move over to our other side of the board and see if we can dissect this out.
10:58
So we have a dash 12 cider notation prefix.
11:03
So what that is telling us is we have 12 ones in as our prefix for our sub net mass for translating. It's a binary. So we have 12 ones in a row. So it's going right. Everything out.
11:16
So we have
11:18
11111111
11:24
It's eight ones.
11:26
Then we have four more ones.
11:30
So we have 12345678.1234
11:35
Now, we don't just put another dot there. We have to finish out the zeros there.
11:39
So we have to finish out the octet. So we write four more zeros,
11:43
and then everything else is zero. Because we know that our first octet
11:50
is all ones. We automatically know that. Okay, on all one's in an octet is 2 55
11:56
So that's the easy one. We also know that all zeros equal zero,
12:01
so those are also very easy.
12:03
But what about this second octet here? How do we need to actually do our equation? And we need to break out our chart in order to figure out Okay, What is this second octet them? Let's go ahead and break out our chart. And we have our 1 28 place 64 30 to 16 8
12:22
for
12:24
two and then one.
12:26
Now,
12:28
if you know that 1 28 is gonna be your highest, you can just start with 1 28 and then go backwards, Toe one. That's just easier for me. But when you're first learning in your first creating these charts
12:39
to avoid not
12:43
putting the correct numbers are not putting enough. You may want to start with one and then increments your way up going to eight places. So instead of going backwards, our highest lowest like I did, you could go. 1248 16 32 64 1 28 Just by habit, I go from 1 28 down.
13:01
Now we take our second octet here
13:03
and we just simply filling our chart. So we have four ones. 1234 followed by four zeros. 1234 So now we just do our math and we figure out what number this is.
13:16
13:20
13:22
and that's going to give us 1 92
13:26
1 92
13:28
plus 32
13:31
and that's going to give us our
13:33
2 30 Excuse me to 24.
13:37
So 1 90 plus 32 is gonna give us our 2 24
13:41
and our 2 24 plus our last one here 16
13:46
is now gonna give us 2 40
13:50
So we don't add any of the rest of our values in this octet because they're all zeros.
13:56
So
13:58
if we wanted to, we could ride out.
14:01
Plus zero plus zero plus zero plus zero. But it's the same is
14:05
just finishing at our 2 40
14:09
and saying
14:09
that's what our octet is now. If you were dissecting a standard I p address, then you would want to make sure you went all the way to the end because an I P address could have another one. In one of these additional places. Cider notation is on Lee ones from left to right. And then it'll stop. And then it'll be zeros
14:30
the same with our sub net masks because our cider notations represent our subnet masks.
14:35
So
14:39
14:41
is gonna be to 40. And yes, that is my final answer.
14:45
So our sub net mask a dash 12 prefix if we translated it into a standard form sub net mask would be to 55 to 40.0 dot zero.
14:56
So
14:56
why do we use cider notation? Why don't we just write out everything as 2 55 to 40.0
15:03
or whatever our cider imitation comes out to be?
15:07
Well,
15:09
cider notation gives us a little bit more.
15:13
It saves us a couple steps per se. Um,
15:16
let's say if we are writing out an I P address and we are modifying or adjusting the amount of bits in that sub net mask. So instead of writing it out as our standards of mathematics, we just write. It is Dash 12 that saves a network engineer. That saves us from having to say, Okay,
15:35
well, 2 55 to 40 0 does. Here, let me break out my chart and let me take my chart and,
15:41
um, I'll go in and I'll take
15:43
this and all translated back to the binary and count out with ones. And oh, that's a Dash 12 prefix. It's easier to work with cider imitation when we're working with sub nets. Which one? Which we'll talk about in a little bit because it tells us the exact number of bits right away.
16:00
It's sometimes easier to work with cider notation than it would be to work with our standard sub net mask in the actual number form.
16:07
Also, it gives us a way that we can write things shorthand we don't have to ride out
16:12
are. If we were writing out an I P address, we wouldn't have to write out. Okay, this I p addresses 1 92.1 68.1 dot 15 with a sub net mask of 2 55.2 55.0 dot zero. We could just right out
16:33
okay,
16:33
this isn't this I p address is 1 92.1 68 that 1.15
16:41
slash
16:42
16.
16:45
We'll be using insider notation or if we were using a standard subject mask for our Class three Class three address 1 92 A Dash 16 on this address would be doing some netting, which we'll talk about in our next module. But if we were using our standard Class three our Class C sub net mask
17:03
for 1 92.1 68 at 1 15
17:07
we would just be putting our Dash 24
17:10
and a Dash 24. If you understand cider notation, you say OK, 24 is an increment of 88 16 24 that equals 22 55.2 55.2 55.0.
17:25
And the more you work with cider notation, the more you work with networks and I p addresses, and sudden it masks, the more you'll come to identify those. So you see the Dash 12 and
17:37
this. Because this may have been the first time you've looked at it, you had to do the math. You had to break it down into your chart and say, OK, that means that means to 55 to 40.0 But after you see dash 12 20 different times,
17:53
then you immediately *** dash 12. That's 2 55 to 40.0 dot zero,
17:59
and you save yourself some writing by just writing it. Outsider notation.
18:03
So
18:03
cider notation we need to understand, because we're in Network Plus and we're working with networking, working with I P addressing, and it's very critical to understand how cider notation works, especially moving on into submitting

### CompTIA Network+

CompTIA Network+ training and certification provides you with the education to begin a career in network administration. This online course teaches the skills needed to create, configure, manage, and troubleshoot wireless and wired networks.

### Instructed By

Anthony Harris
Systems Analyst and Administrator at SAIC
Instructor