Subnetting conflicts between tests

MS Press 70-291 wrote:

To determine the number of subnets available within an address space, simply calculate
the value of 2y, where y equals the number of bits in the subnet ID.

MS Press 70-293 wrote:

Because you have allocated 8 bits to the subnet identifier, you can create
up to 254 subnets on this network (28–2=254).

Now my question is why would they tell you to determine the number of subnets one way for one exam and another for the other. Way to go M$!!!

So is 2x-2 the correct way to determine the number of available subnets for the 70-293 but just simply 2x for the 20-291?

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Comments

bighornsheep

2^x-2 is following RFC 950, an older standard that subtracts subnet of all zeros and subnet of all ones thus minus 2 from the formula.

2^x is a following a newer standard for hardware which supports it. I believe all of Microsoft's current exams covers hardware+software that is the newer RFC. So 2x should be the right method to calculate custom subnets.

Silver Bullet

bighornsheep wrote:

2x-2 is following RFC 950, an older standard that subtracts subnet of all zeros and subnet of all ones thus minus 2 from the formula.

Yes, thanks but I am aware of that. My question is why use one method for the 70-291 and another for the 70-293.

And if 2x-2 is used on the 70-293 instead of 2x like was used for the 70-291?

bighornsheep wrote:

I believe all of Microsoft's current exams covers hardware+software that is the newer RFC. So 2x should be the right method to calculate custom subnets.

One would certainly think so but according to MS Press for the 70-293 this is not the case. Looking for some insight from someone who has taken the 293.

bighornsheep

Silver Bullet wrote:

And if 2x-2 is used on the 70-293 instead of 2x like was used for the 70-291?

I have no idea why Ms Press will write 2^x - 2? I beg to think different. mcgraw Hill, Sybex, Que materials for MS exams uses 2^x.

In any case, the formula should not be different for the two exams.

http://www.techexams.net/forums/viewtopic.php?t=17881

Silver Bullet

And it may not be different between the exams. It may be a mistake in the MS Press 70-293 book. That is why I am looking for some confirmation from someone who has taken the test.

royal

Definitely go with 2x for subnets and 2x-2 for hosts.

eurotrash

I can't remember what was used, but a look at my Syngress book tells me that you don't subtract 2.
Also a look through some of my earlier posts from the time I was studying for the 293 suggest the same thing.
I also said "it depends if they are asking 'how many subnets' or 'how many usable subnets'", so keep that in mind too.

Webmaster

Is there a big difference between the dates your 291 and 293 books has been published? For the CCNA exam it's obvious, don't subtract the 2 unless there's a rather clear hint. And for the 2000 exams, you need to subtract the 2, the traditional way ('old' would describe it better). Based on some comments in the topic Bighornsheep linked to, it seems for the 2003 you don't have to subtract the two. There shouldn't be a difference in the 291 and 293 exam, nor the guides for those exam from the same publisher. I suggesting contacting MS Press and point out the inconsistent paragraphs (and let us know what they come up with

Silver Bullet

_omni_ wrote:

I can't remember what was used, but a look at my Syngress book tells me that you don't subtract 2.
Also a look through some of my earlier posts from the time I was studying for the 293 suggest the same thing.
I also said "it depends if they are asking 'how many subnets' or 'how many usable subnets'", so keep that in mind too.

Thanks

Webmaster wrote:

Is there a big difference between the dates your 291 and 293 books has been published?

291 = April 13, 2003
293 = May 17, 2006

With looking at the publish dates you would think that it would be the other way around.

I'm beginning to think that whoever wrote that section of the book was in the bottle that day and was reminiscing. GOOD TIMES.... Good Times

Webmaster wrote:

I suggesting contacting MS Press and point out the inconsistent paragraphs (and let us know what they come up with icon_smile.gif).

If I find time I may do that. Although I doubt they would pull all of those books from the shelves for this one inconsistency.

shamrocker98

I would trust the 70-291 MS book. The 293 was worthless and the author was not an MCSE himself.