# Host IDs

I taking a class "Networking Essentials" Subject "Binary Numbers" I am lost.

Define a range of host IDs for the the following subnet: Network ID of 150.17.0.0, subnet mask of 255.255.255.0, and 4 subnets.

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Commented:
You have B-class address, but your subnet mask suggests that you have only 256-2=254 IP addresses for your hosts available. Now you want to divide your network into four subnets. Binary 11100000 or 224 has 3 masked bits and 5 unmasked bits. Therefore using subnet mask 255.255.255.224 you can have up to 6 subnets (2x2x2-2). For your 4 subnets you can choose out of the following ranges:
150.17.0.32 to 150.17.0.63
150.17.0.64 to 150.17.0.95
150.17.0.96 to 150.17.0.127
150.17.0.128 to 150.17.0.159
150.17.0.160 to 150.17.0.191
150.17.0.192 to 150.17.0.223
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Commented:
From that data (IP 150.17.0.0 and a subnet mask of 255.255.255.0) there are 254 standard subnets (255 if you use subnet-zero). The question asks for four subnets and the first four standard subnets would be:

150.17.1.0 (IP's 150.17.1.1-150.17.1.254)
150.17.2.0 (IP's 150.17.2.1-150.17.2.254)
150.17.3.0 (IP's 150.17.3.1-150.17.3.254)
150.17.1.0 (IP's 150.17.3.1-150.17.3.254)

And the last subnet would be:

150.17.254.0 (IP's 150.17.254.1-150.17.254.254)

All the subnet mask does is to specify what part of the IP is the network portion and what part is the host portion. If you convert both the IP and the subnet mask to binary quads and logically AND each quad the result is the network quad. In this case (it's simple) the network portion in 150.17.n and the host portion is 0.0.0.n.
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Commented:
255.255.255.0 uses 150.17.0.1 to 150.17.0.254 (classful routing, you lose network and broacast addresses).
We usually break something like that with 26 bit subnets (255.255.255.192)
..1 to .62
..65 to .126
..129 to .190
..193 to .254
Given that most of our sites are roughly the same size. You could break it up many different ways, though. Rewording what jlevie said, the subnet just defines how many IP addresses you can have "in that building". You can, of course, have many subnets in one physical building, it's just a good way to visualise it.
Can't remember where, but I downloaded a demo version of a subnet calculator at work. There's a few of them out there, and can be quite handy (saves doing the math in your head) and can be useful in teaching subnetting.
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