Ambiguous questions regarding subnetting (subnet zero)

Hello everyone,

Should I assume that when not stated, subnet zero is assumed to be in use?

Clarification: I am speaking about questions where the mask is given and you have to calculate available/usable subnets/hosts.

Like for and example /28

This gives us 16 subnets with 16 IP addresses in each. There are 14 usable IP addresses in each case.

With subnet zero we can use 16 subnets.
Without subnet zero we can use 14 subnets.

So, how can I know for sure, whether the subnet zero is in use if it is not stated and what would be the default value to assume (I tend to think that it would be that subnet zero is used)?

This has me frustrated since previous attempt.

Oh, I didn't mention it. I am sitting the exam tomorrow and I am comfortable with subnetting, just that ambiguous questions tend to drive me into frustration fields.

Hoping to hear some comments from you,
Inc

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Comments

Webmaster

Hello,

This question has been discussed several times before. You can find the topics in our CCNA FAQ in the Subnetting section:

www.techexams.net/forums/viewtopic.php?t=7268

Inc

I apologize for being so ignorant. I have checked the FAQ thread before, just didn't pay enough attention to notice subnet zero questions.

Webmaster

Don't worry about it, better late than never

Inc

I did additional (re)search and found the following quote (comes from cisco ccna prep forums)

Hi. Martin Benson here, I work with the team that creates the INTRO, ICND, and CCNA exams.

The test items on the CCNA exam will tell you whether ip sunbnet-zero is in effect or not. In general, you should assume for the CCNA that all subnets are usable unless the question indicates otherwise. There will always be enough information given in the question to indicate which subnetting scheme is legal for the problem space.

Hope this helps.

Martin

In hope that this information will help someone else too.

Webmaster

Exactly as I've been saying for years, but very nice to see if confirmed. Thanks for sharing that.