# tcp/ip subnetting version 4

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Ok I'm studying for my network+ exam the only thing I'm seem to be a little unsure on is calculating users and hosts using the subnet masks. Ok so here is the thing you calculate how many subnets by 2n when equals the number of bits so in other wards 2*8 power 256 the concept is the same for hosts except you subtract two you get 254 that gives you your default subnet mask of 255.255.255 but lets say my network needs this is the class c standard. So all I need to do to increase client capacity is adjust my gateway mask address. In other wards if I adjusted 255.255.250 that would give me an extra 38 hosts? And an extra 40 subnets?

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Also just I understand basically since were using a class c standard we divide the client between the subnets because we can only give out 254 ip addresses to each subnet

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255.255.250.0 would not be a valid subnet, but 255.255.248.0 or 255.255.252.0 would be. The guys voice is annoying to listen to but this video is a great introduction to and explanation of IP address subnetting.

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That would be 276 users right?

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And 278 subnets right? Have I finally got the math down?

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What would be 276 users?

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A 255.255.252.0 subnet mask would allow for 1024 addresses with 1022 usable. Watch the video I linked to. Lots of good information there.

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Ok I think I have this now...ok you get the number hosts by doubling each number starting by 2 in other wards if you wanted 512 hosts it would take 9 bits. But in reality you would only have 510 hosts so If I wanted 512 valid hosts I would have to move up to 11 bits. That would also give us the same amount of subnets 512 because you use the same method just count left to right instead of right to left. Now calculating the subnet mask is simple since this is a cider 23 know the first 2 bits will be 255.255. Now since nine bits are left we basically easy way to do it is count right to left so since 8 bits would give us a dot zero for the last bit we wind up having one bit left making it 255.255.254.0

So how did I do?

Edited by Jklein

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So basically how many hosts will give you how many bits once you know that bits will give you your subnet mask. Which is calculated by cider in other wards if I take in otherwards if my cider is 25 my subnet would be 255.255.255.254 that's what happens when you try to do math at 1:30 in the morning

Edited by Jklein

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Wait no 128 not on 254

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Jklein,

Just wanted to chime in and say if you need help subnetting let me know. I'm net+ and ccna certified(though expired, 2007).

Always willing to help a fellow networking guy.