Help on subnetting question off university quiz

Unanswered Question
Mar 7th, 2008

I received this question from a university instructor on a quiz. The instructor states the answer is no. Can someone please provide the correct answer with explanation.

Thank you, Greg

Your company is issued a class C address of However, your company has three locations that need three separate network addresses. Each network is required to have at least 50 node addresses. Is it possible to accomplish this with one class C address?

I have this problem too.
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hugo_garcia Fri, 03/07/2008 - 09:40

you can use for 4 subnets, each with 64 nodes



Richard Burts Fri, 03/07/2008 - 12:38


If the instructor follows the traditional (and very outdated) approach that subnet zero is reserved and can not be used for host addresses then the answer is that it can not be done. In terms of real life current practice then Hugo is quite correct that it can easily be done by creating 4 /26 subnets.

Perhaps the other twist to the question is whether you are also supposed to get addresses for the links that connect the sites out of that same address. But I suspect that the instructor was just using the subnet zero issue.

[after posting I re-read the original post and find it a bit ambiguous. I interpreted it as involving a HQ and 3 remote sites. And in that case I believe that my response is correct. But the question strictly interpreted says 3 sites. I am not sure that I see any problem if it really is about 3 sites.



Richard Burts Fri, 03/07/2008 - 13:31


Thanks for noticing. I have been busy doing a presentation for Cisco to Cisco users in the Northern Virginia/DC/Maryland areas and off line for a couple of days. Now I am back.



lamav Fri, 03/07/2008 - 14:12

Of course I noticed! Without you, there's no one to argue with me! ;-)

Glad you're back, buddy.

Joseph W. Doherty Fri, 03/07/2008 - 16:14

Perhaps the other possible reason for a "no", if the C address of is provided as an actual public IP address block, you often can't just split it up and use it where you will if the subnetted addresses are to be advertized back to the Internet from different Internet connected link locations.

BrinksArgentina Sun, 03/09/2008 - 17:19

If the network provider is the same in all locations, it can be easly done. If the not, you need to spend a lot of time using your phone! :)

You will need an ASN for each location.

Joseph W. Doherty Sun, 03/09/2008 - 17:33

You must work with some very cooperative providers!

Kidding, aside, you make an important point.

Usually not an issue if all your locations connect to the same provider's POP, can be an issue when working with the same provider but POPs are different, especially in different countries.

greg.battista Wed, 03/12/2008 - 11:44

Thanks for all your responses. The original question was worded exactly as above and I don't think it is as complicated as involving multiple ISPs. I agree that it can be accomplished with a /26. I don't think that subnet 0 is a consideration here as it is now turned-on by default. The truth be told I can't get a straight answer from the this instructor and since its an online class communication is even more limited. Again thanks for all your input - it helped keep me straight.



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