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IP subnet mask questions

Posted on 2010-11-15
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Last Modified: 2012-06-27
Hello,

I've a computer with IP 191.1.12.129 and there are 2 subnets defined. I need help with the following questions:

- How many bits are used for the subnet mask?
- How many bits are used for hosts addressing?
- How many subnets are not used?

Thanks in advance for your help. I'm new to networks and I really need your help.

jppinto
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Question by:jppinto
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Qlemo earned 167 total points
ID: 34141167
Without supplying a net mask, we need to derive the netmask from the IP address. 191.1.12.129 is in the range of 128.0.0.0 to 192.0.0.0 (exclusive), which is a Class B subnet with mask 255.255.0.0.

If you have any doubt or question, use http://www.subnet-calculator.com/ to check for available networks, how much bits are used for the mask or hosts, aso.
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by:jppinto
ID: 34141237
Hello,

I know that this IP address is a class B subnet...at least that I know :)

I need to know the rest of the information.

jppinto
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Expert Comment

by:Qlemo
ID: 34141265
As I said, use that calculator site. And some common sense. A mask of 255.255.0.0 is how much one's bits from start (left)? The answer is: 16. That is the same with each Class B subnet.
Host bits are all bits that are zero, counted from right. Again, this are 16.

I cannot answer the rest, because your question is not complete. What IPs do your 2 subnets consist of?
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by:avilov
ID: 34141299
on that computer if you run command

ipconfig /all (winodws)
ifconfig -a (*nix)

what is teh output?
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Assisted Solution

by:Fred Marshall
Fred Marshall earned 166 total points
ID: 34142305
I've a computer with IP 191.1.12.129 and there are 2 subnets defined. I need help with the following questions:

What do you mean by "there are two subnets defined"?  Please illuminate.

- How many bits are used for the subnet mask?
It dpends on the subnet mask.   :-)

- How many bits are used for hosts addressing?
It depends on the subnet mask.  :-)

- How many subnets are not used?
This depends on your answer to the question:
What do you mean by "there are two subnets defined"?

This IP address *could* have a subnet mask of 255.255.255.252.
In that case there could be 16,384 subnets with 16383 unused.
There would be 2 bits for host addressing yielding 2 hosts per subnet after the network and broadcast addresses are used up.
The subnet mask uses 30 bits.

But, there are many other possibilities!!

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by:jppinto
ID: 34143772
What do you mean by "there are two subnets defined"?  Please illuminate.
I can't tell you what this is, this was the information I was given...

It depends on the subnet mask
I believe the subnet mask is 255.255.128.0 (using the calculator)

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by:Qlemo
ID: 34144159
Guessing does not help. You need to know, else you (and we) can't answer the questions.
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by:Otto_N
Otto_N earned 167 total points
ID: 34146512
jppinto

Is this a question you need to answer (like homework), or is this a real-life example?  The way to solve this will depend on the situation:  In real life, additional information can be obtained.  In a posed question, you're stuck with the info you're given, and it usually aim to test knowledge, even of archaic information (like classless subnetting).

I'll assume that it is something like a homework question.  By the way, as an Expert yourself, you are aware of the homework policy of EE.  So please indicate the context of the question, as I have been berated by a Mod before , and do not want to repeat the experience!

The question, as posted, is not very clear:  It can be interpreted in many ways, in my view.  That is also why most experts that commented up to now asked for more info.  But before you can even interpret a subnetting question, you need to at least understand the fundamentals, such as the difference between classless and class-based subnetting.  I always liked the TCP-IP guide's explanation of IP addressing: http://www.tcpipguide.com/free/t_IPAddressing.htm. It is quite a chunk of info, but very thorough and easy to follow, and I have yet to find a single error in it.

Once you grasp the gist of IP addressing and subnetting, you will find that a) you interpret the question differently, and b) that a tool like subnet-calculator are easier to use.

Since, by your own admission, you're new to networking, please spend a couple of hours to grasp the concept of subnetting.  You might find that the answers are actually trivial.

Above ramblings are based on a couple of assumptions.  If I'm of the mark, please do not hesitate to correct me.  Or perhaps you want to re-word the question...
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LVL 33

Author Comment

by:jppinto
ID: 34146643
This is a real situation that I got stuck in! This is not clearly my area of expertise! I was asked for help from my boss and even after I told him that this is not my area, he still insisted in my participation!

I will try to learn a little more about this and will read the material at the link you recommend. I will tell him that I can't answer the questions he asked me and will close the question by awarding the points to all that participated and will not spend more time with this. As you all said, this is a little like "shooting on the dark" and without more information it's hard to give him a correct answer.

Thanks for the help.

jppinto
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Expert Comment

by:Otto_N
ID: 34154511
My deepest sympathy, and the very best of luck!

If I can give you some pointers for a future question on this matter:  Indicate where the information ("computer with IP 191.1.12.129 and there are 2 subnets defined") comes from.  Is it a verbal message from your boss, or a phrase in a supplier's documentation or a test report from a work colleague?  This will assure that responses will be applicable to your situation.

My other concern is the nature of the questions itself:  I know of no specific application where it is required to specify the number of bits used for networks or hosts, or the number of unused subnets.  Usually it is only used in quizzes to test knowledge of subnetting.  Again, knowing the source of the question could provide some clues.

Let us know if you have any update on the issue!
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by:jppinto
ID: 34154538
Thanks for your support... :o)
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