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Variable Length Subnet Masking

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Time
8 hours 19 minutes
Difficulty
Beginner
CEU/CPE
8
Video Transcription
00:00
Our next topic is variable length subnet masking
00:04
even though it sounds challenging and complicated. It's very simple.
00:09
It does require an understanding of the material we've discussed in previous sections of this chapter.
00:15
It's just submitting based on number of hosts or on number of subnets
00:20
were either submitting to steal additional ones or additional zeros.
00:24
Variable length subnet masking means each subnet. It can use its own sub net mask.
00:30
If you have a larger departments within your organization,
00:33
you don't have to have a one size fits all mask for your whole company.
00:37
If you have 2000 hosts to support in one sub net and 15 and another, it doesn't make sense to use the same sub net.
00:44
This goes back to the days where routers only understood the classical add dressing scheme we discussed
00:50
when we didn't have a lot of flexibility with R. I. P addresses.
00:54
That was a long time ago.
00:57
Variable length subnet masking allows us to figure out what's necessary at each network and use the appropriate mask.
01:03
In this instance, we started off with an I P address on the 172.30 point 232.0 network,
01:11
which is a Class B.
01:14
I'm making a mental note of that.
01:15
We can also see here how many devices each network needs to support.
01:21
And I'm thinking of binary zeros.
01:23
I need 57 devices in the binary zeros.
01:26
I know that in order to make this happen, I'll need to use a sub net mask.
01:30
So let's jump over to the answers.
01:34
I'll need to steal 40 sat six bits to zero
01:38
for HR. I only need 23 devices,
01:41
so I'll set five bits to zero to the power of five. Minus two
01:46
30 to minus two means 30 devices would be supported.
01:49
I need 12 devices in it and to support 12. I'll steal four bits and four bits will be set to zero.
01:57
The remaining would be set to one, so I have 28 ones
02:01
then. Our Finance department has 32 devices.
02:05
We use the slash 26 mask again.
02:08
Marketing uses nine devices and also the 20 bit mask.
02:14
In this case, each department gets their own mask. Nothing too exciting
02:19
for the next question. It's assuming we want to contain all of these on a single network and forget about submitting.
02:25
We'll bring them back into the fold without sacrificing any more host addresses than we have to.
02:31
The idea here is if you go with slash 26 were choosing the smallest number of binary ones because it's going to encompass the greatest number of host addresses.
02:42
If you have an environment where there is a variable length subnet masking, then the question arises that says, Incorporate all of them on the same network.
02:50
Choose the lowest address.
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