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SubnetMasks

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December 2, 2009 4:17:51 PM

Hi again, I'm seeking your aid with a doubt I have, lets say I have my router connected to and ISP, and to that router I'm going to connect some switches to distribute the network on 200 different computers. Now out of this 200 computers I want to create different subnets, one with 10 computers, one with 30, one with 100 and another one with 60.

I'm thinking since the most computers I need is 100 I would use a subnet like this 255.255.255.128, but, would I have to use that subnetmask for all the subnets? I guess the question is, can the single router manage different subnets to, for instance, set a subnetmask of 255.255.255.140 for the subnet with 10 ps and a subnet mask of 255.255.255.129 for the one with 100? this considering the setup with a single router and switches that I descibed. But I'm not sure this would work because then one subnet would go from ip 0 to 15 and the other would go from ip 16 to 144?

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December 4, 2009 7:20:30 PM

Why exactly do you want to create subnets?

If your router can handle it is the first issue. It depends. If you have a good quality router, it won't be an issue. If you have a small SOHO Linksys 5 port Router & switch combo, you will have issues with it.

In order to figure out your subnets though, you have to determine how many subnets you want and how many computers are going to be on each subnet. When you subnet, you break up a class of IPs into sections to limit some network traffic. You would ideally do this if you had a switch available for each subnet. This would keep traffic off each other when the switch is broadcasting and looking for other devices, etc.

Considering the size of your subnets, I don't know that you want to do what you're thinking. In order to determine your "stepping stone" to figure out what to subnet at, you have to figure out what the max number of computers will be on each network. In your case, 100 at most on one subnet. Your stepping stone would be 128 though, giving you only 2 subnets available. You have 256 available spots on a single network, you take 100 away for one subnet and based on that you stepping stone has to be 128 which cuts your network in half.

Depending on the capabilities of your router, you may want to look into what is referred to as SuperScope where you can additional Networks into a single Subnet (255.255.255.0).

How I determined what your stepping stone would be is kind of simple. First, you break down the subnet into halves. After that, you determine how many computers will be on the subnet (which are represented by the ones) and they add up to 100. Everything to the right of the left most 1 turns into a 1. You now have a neat list of 0s and 1s. Add all the 1s together to determine your stepping stone. The stepping stone is the increment in which your subnet goes. 255.255.255.128/129.

Also note this is in the idea you're going to be using the same Class C network address of something like 230.230.230.x. You could use the Reserved Business Class IP Scheme of 10.x.x.x which is a Class A with a subnet mask of 255.0.0.0. With that you could definately achieve your subnets.

Anyhow, stepping stone - pardon the crudeness of it all.

128 64 32 16 8 4 2 1 (subnet broken down by halves)
0 1 1 0 1 0 0 0 (1s total the number of computer you want on the subnet)
0 1 1 1 1 1 1 1 = add the "halves" above the 1s to determine the stepping stone.

In this case you come out to 128.
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