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Posted on 2010-09-15
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I have very little knowledge of IP addressing and I would appreciate some help here

I have an assigned range of 75.137.45.144/28. How many machines can I connect to it and can I make it into two equal sized subnets? How?  Is there a Math formula to figure this stuff out??
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Question by:dawber39
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Expert Comment

You can have up to 14 devices in this range. For your info the subnet mask would be 255.255.255.240

If you want two subnets, then they could have only 6 devices each. They would have ranges of 75.137.45.144/29 and 75.137.45.152/29 and the subnet mask for these two subnets would be 255.255.255.248
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Accepted Solution

Qlemo earned 500 total points
with a /28 you have 32-28 = 4 bits = 16 addresses left for your hosts. You need to subtract two for the reserved addresses of all-zero and all-one bits, so in fact you can use 14 addresses. If you subnet that, you loose 2 addresses per subnet for the same reason. Your subnets would then be
75.137.45.144/29 with .145 - .150
75.137.45..152/29 with .153 - .158
that are 6 addresses per subnet = 12 overall.

The /28 part tells us how much bits from the left to the right are assigned to the network. Each part of the address is a single byte = 8 bit, 4 parts = 32 bits, and /28 is 32-4, which means 4 bits are left for the hosts.
We can only add bits on the highest part of the host addresses for implementing subnets, so the next bit to use for a subnet is bit 29, which has a value of 8 (2 power 3).That is why the next subnet starts at 152 (144+8).
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Expert Comment

>I have an assigned range of 75.137.45.144/28. How many machines can I connect to it and can I make it into two equal sized subnets?

This depends on whether or not you are assigning this range to an interface; if all you are doing is defining static one to one NAT, then you can use all 16 addresses; if you are however, assigning this to a physical interface on a firewall/router, you will then need 1 IP address for the physical interface then you will have 13 usable addresses for your hosts on this LAN.

Billy
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Author Comment

I appreciate the efforts of all of you - but Qlemo gave me a better explanation of how - thank you all
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Author Closing Comment

Excellent
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LVL 35

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If you "appreciate the efforts of all" you should really be sharing the points... but whatever!
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too bad you can't block authors!
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Author Comment

Wow - all I did was ask how - and Qlemo was quite definitive in his explanation - I am sorry if I hurt your feelings
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