Variable Length Subnet Masking

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Our next topic is variable length subnet masking

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even though it sounds challenging and complicated. It's very simple.

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It does require an understanding of the material we've discussed in previous sections of this chapter.

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It's just submitting based on number of hosts or on number of subnets

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were either submitting to steal additional ones or additional zeros.

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Variable length subnet masking means each subnet. It can use its own sub net mask.

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If you have a larger departments within your organization,

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you don't have to have a one size fits all mask for your whole company.

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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.

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This goes back to the days where routers only understood the classical add dressing scheme we discussed

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when we didn't have a lot of flexibility with R. I. P addresses.

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That was a long time ago.

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Variable length subnet masking allows us to figure out what's necessary at each network and use the appropriate mask.

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In this instance, we started off with an I P address on the 172.30 point 232.0 network,

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which is a Class B.

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I'm making a mental note of that.

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We can also see here how many devices each network needs to support.

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And I'm thinking of binary zeros.

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I need 57 devices in the binary zeros.

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I know that in order to make this happen, I'll need to use a sub net mask.

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So let's jump over to the answers.

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I'll need to steal 40 sat six bits to zero

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for HR. I only need 23 devices,

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so I'll set five bits to zero to the power of five. Minus two

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30 to minus two means 30 devices would be supported.

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I need 12 devices in it and to support 12. I'll steal four bits and four bits will be set to zero.

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The remaining would be set to one, so I have 28 ones

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then. Our Finance department has 32 devices.

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We use the slash 26 mask again.

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Marketing uses nine devices and also the 20 bit mask.

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In this case, each department gets their own mask. Nothing too exciting

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for the next question. It's assuming we want to contain all of these on a single network and forget about submitting.

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We'll bring them back into the fold without sacrificing any more host addresses than we have to.

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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.

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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.