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Classless Inter-Domain Routing (CIDR) to Create Subnets Part 1

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Time
8 hours 19 minutes
Difficulty
Beginner
CEU/CPE
8
Video Transcription
00:00
IP addressing or classical IP addressing everything that we've discussed work so far.
00:05
What we're going to get now is some of the limits of using a classical addressing system and moving to a classless system.
00:12
This is referred to as C i d. Are classless inter domain routing.
00:18
This is going to give us the ability to submit our network.
00:21
Somebody means I'll take one big network, id the 10 Network and break it into smaller networks. So I have 10.8 10.16 10.21 network. However I choose to submit.
00:33
What will allow me to do is create unique network IEDs within the overarching network idea of my organization as a whole.
00:40
One reason why I might want to do that is to isolate broadcast traffic.
00:44
Routers will isolate broadcast traffic to a specific port.
00:48
So if I have the sales domain and they have an application, that journey, it's a lot of broadcasts. I don't want those broadcasts going throughout my network.
00:55
I can put them on their own sub net, and their broadcast would be limited there.
00:59
I may also want to create unique security domains,
01:02
for example, For one, my HR computers because they have a list of payroll information and other sensitive data.
01:08
I may have avoid network to prioritize traffic, or I may just want to break them up my network into smaller, easier subnets.
01:17
Don't forget what type you have said that masks that separate network portion and host portion.
01:22
Hopefully, we've laid the groundwork for what we're going to do now.
01:25
You've already said binary ones in the sub net mask indicate a network address,
01:30
whereas zero in the sub net mask indicates a host.
01:33
So we're certain talk about things in binary hold that thought for just a minute.
01:38
The thing that's so rigid about classless addressing is an entire octet is either network or host.
01:45
When we see this looking over on the right side here, classical addressing is inherently wasteful.
01:51
Why is that?
01:52
If you look at the four octaves and see a full octet, is either network support a host support?
01:57
Then, if we start with Class A sub net mask, which is the 1st 255.0 point 0.0, I've got three octaves for hosts
02:06
that will support 16.7 million hosts. That's a lot
02:09
the way we figure that out is each octet has eight series for the whole going back.
02:15
The way we figure that out is each octet has eight zeros for the host portion.
02:21
The formula is two to the power of X, where X is the number of zeros
02:25
you find your value. But then you also have to subtract two because we have to count from the network ID and the broadcast address.
02:34
So when we look at two to the 24th power minus two, we come up with about 16.7 million hosts.
02:40
We go down a Class B
02:43
and we have support for two to the 16th power,
02:45
which is 65,000, 356.
02:49
We subtract to account for network idea broadcast.
02:52
So you have support for 65,354 hosts.
02:57
Class C only has one octet
02:59
or eight bits to support hosts,
03:01
so you have to. The power of six minus two gives us support for 254 hosts.
03:07
So when I say this is inherently wasteful,
03:10
let's imagine I have 255 hosts.
03:13
I can't use a Class C.
03:15
I have to go all the way up to Class B, which means I'll waste about 65,000 I p addresses.
03:22
That's really wasteful.
03:23
When you're talking about trying to manage IP addresses in an enterprise environment,
03:28
you don't want a huge range of available addresses.
03:30
People could take advantage of those IP addresses that would be on the same network,
03:35
and that may be a security concern.
03:38
But it's just inefficient.
03:39
A lot of this goes back at the time when we purchased a Class C address or a Class B,
03:46
if we were a huge organization, we purchased a Class A.
03:50
We never want to pay for more than what we need. Same idea today
03:53
when I have an Internet presence, I have to pay for my IP addresses that are on the Internet,
03:59
which is why it's important to choose the correct number.
04:02
We've got a very rigid scheme that's inherently wasteful.
04:05
So what we want to assess is how we can make it less wasteful but also divide our networks up into additional substance.
04:13
We'll take a basic network ID
04:15
10 point x point X point x with the 255.0 point 0.0 sub net mask.
04:21
I want to show you the mask in binary,
04:25
we have eight binary ones. The next three octaves are eight binary zeros.
04:30
In this case, the first octet is already taken.
04:32
I think of it this way because the first octet will be reserved for the network ID because it starts with being a Class eight address.
04:41
The first octet we don't work with.
04:43
And the second Oct. It, however, take note of all the zeros
04:46
here and in the rest of the sub net mask.
04:49
There is support for 16.7 million hosts, which I have no need for.
04:55
I'd like to trade some of those hosts for networks or subnets,
04:58
and thinking about this will trade zeros for one in our sub net mask.
05:01
And that's how we will create additional subnets.
05:04
We're swapping the zeros to ones that are sub net. Masks will change.
05:09
We'll be sending bits, so to speak, going back.
05:14
What were you splitting bits, so to speak?
05:17
Let's take a look at submitting when working with the classical address.
05:20
For example, let's say I have a class A mask
05:24
which normally is eight binary ones and 24 zeros.
05:28
If I want to create additional networks for myself,
05:30
trade some host support for network support,
05:33
I go to the next bit of the second octet and trade it from 0 to 1.
05:38
In binary that becomes 255.128 point 0.0.
05:45
What's the purpose of doing this?
05:46
I created new networks
05:48
every bit I steal. I create two to the power of X networks,
05:53
where X is the number of bits stolen.
05:56
By changing that first bit from 0 to 1, I created two to the power of one network.
06:00
So I created two networks.
06:02
Just by modifying the sub net mask and stealing or splitting bits, I can create additional subnets for myself.
06:10
What if I wanted to create four additional networks?
06:13
I still two more beds or a total of two beds.
06:16
If I steal the first two bits, that would be 255.1 night. 2.0 point zero
06:23
into the power of X networks will be created
06:27
in this case to the power of To will give me four new subjects.
06:30
This continues. The more networks I want, the more bits I borrow.
06:34
Don't forget that changes your sub net mask, which is why knowing a bit of binary does help
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