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IP Address Assignments & Subnets

Posted on 2015-01-27
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I am studing IP addresses and subnetting. I recently took a test and there were two questions I couldn't answer. The file has the correct answers noted by a red dot by the correct answer.

My question is with the information presented in Question 14 & 15 how do you know you are creating "four separate" subnets. I think I understand assinging the system IP address of 172.17.0.1 as it is the first usable IP address after the 172.17.0.0 network.

What I mostly don't understand is how you know from the info presented do you have 4 subnets. Is there a way graph this out on paper?

I have the same question for question number 15.
Subnets.pdf
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Question by:James Coats
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Trenton Knew earned 500 total points
ID: 40573471
using that subnet mask ( .192) creates 4 subnets because the third octet of the IP address has two bits that belong to the network.  
( I.E. 255.255.192.0 = 11111111.11111111.11000000.00000000 )

so on those two bits (the first is in the 128 bit, and the second is in the 64 bit:
00 = 172.17.0.0
01 = 172.17.64.0
10 = 172.16.128.0
11 = 172.16.192.0 (128+64)
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by:Trenton Knew
ID: 40573478
The way subnetting works, any address that falls into the same range belongs to the same subnet.

the first subnet would include all addresses from 172.17.0.1 - 172.17.63.254
the second subnet would include all addresses from 172.17.64.1 - 172.17.127.254
the third subnet would include all addresses from 172.17.128.1 - 172.17.191.254
the fourth subnet would include all addresses from 172.17.192.1 - 172.17.255.254
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by:Qlemo
ID: 40573484
The info given in the test is incomplete, and assumes classed subnetting. The default mask for 172.17.0.0 is /16 = 255.255.0.0 (a Class B network). Subnetting on that with 255.255.192.0 leads to the 4 subnets, as Trenton described.

But if you throw away the ancient classed subnet assumption, you can't tell which subnets. The first question for subnetting always is "what is my basic subnet mask", because you need to divide something into smaller parts, and you need that something ;-).

That might have been told in prior test questions, and I think it has been.
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Author Closing Comment

by:James Coats
ID: 40573496
OK thank you I see that now. It is a little confusing but that makes sense. I need to make some sort of work sheet to draw it out in a kind of picture / graph. From what you presented here I think I can do that.

So on the first bit (192) you would have IP addresses between 172.17.129 & .191 and on the second bit you would have IP address between 172.17.0.1 & .63 thus providing the 4 subnets you presented.
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by:James Coats
ID: 40573506
Thank you Trenton & Olemo for your comments.  I was reading the first comment and didn't see yours. All the comments have been very helpful.
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by:James Coats
ID: 40573677
Oemo,

I would like to ask a question related to this question but I don't see the option in this new EE. I searched EE and it said use the box at the bottom of the question but this doesn't look like that sort of thing to me. How would I ask a follow up?
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