Question 26 on the Practice exams page 640-801 55 questions)

26. You are designing an IP addressing scheme for a company using classful addressing. You have been assigned a class C network address 192.168.24.0 and you have to divide it into 4 subnets with at minimum of 25 hosts each. What subnet should you use?

a. 255.255.0.0
b. 255.255.255.0
c. 255.255.255.192
d. 255.255.255.224
e. 255.255.255.240
f. 255.255.255.129

Answer(s): d. 255.255.255.224

This question should specify weather or not the IP subnet zero can be used, because if it can answer C is correct....

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Comments

borumas

I agree, I would have chosen c myself, tricky question there as on some practice test c would likely be the answer.

rakem

yea i took C as well, as i have been told that now days the using the zero subnet is fine.

Danman32

In real world yes, you can use subnet zero. But for testing, when in doubt, rule it out.

HELLZxPHADER

I would choose d because it would satisfy the requirements better (closer to 25 hosts).

mp3spy

HELLZxPHADER wrote:

I would choose d because it would satisfy the requirements better (closer to 25 hosts).

Me too, the question specifies 25 hosts minimum. 30 hosts per subnet is fine.....Right!?!?!

Webmaster

Danman32 wrote:

In real world yes, you can use subnet zero. But for testing, when in doubt, rule it out.

We went over this in another topic already, and I disagree. Subnet zero is enabled by default on the IOS versions 'on which the exams are based', and not using subnet zero is an obsolete practice, for several years already, according to the RFCs. It's only a consideration when older systems are in place. I.o.w. on a current Cisco test, always assume the IP subnet zero is enabled 'if' it is not rather obvious based on other hints in the question (all routers run IOS xxx) or when they just flat out tell you (ip subnet-zero is enabled/disabled). Hence, when it comes to the calculation itself, subtract only 2 from the hosts, not from the subnets.

www.techexams.net/forums/viewtopic.php?t=15720

But in that other topic I also already stated that it's a non-issue, because unlike my question the O/P quoted, Cisco won't trick you as in provide a valid answer when subnet zero is enabled and a valid answer for disabled/not supported, without at least a clear hint whether it is enabled.

You can always contact Cisco and ask them if their current tests are based on a recent IOS, and follow their own quotes from subnetting RFCs, and therefore you should assume ip subnet zero is enabled in subnet questions as well.

Yes, this also means I will be giving question 26 an update. I will also go through other 'older' (cause that's what most of them are) subnetting questions to see if I can make them a bit more consistent in regards to giving hints about subnet zero as well as things like whether you have to accomodate for growth .

rakem

^^

Excellent! thanks

zero-g-smith

Hey I could be totally wrong but as I understand it even though the question is about subnets the wording in the quesiton says "classful" which I assumed to mean no using subnet zero even though its enabled by default.

Yankee

Don't get all wrapped up in the subnet zero talk and pay attention to what the question requires. It wants a minimum of 25 hosts, so you give them the minimum acceptable answer which is D, a /27 block.

Yankee

sprkymrk

zero-g-smith wrote:

Hey I could be totally wrong but as I understand it even though the question is about subnets the wording in the quesiton says "classful" which I assumed to mean no using subnet zero even though its enabled by default.

Yankee wrote:

Don't get all wrapped up in the subnet zero talk and pay attention to what the question requires.

I need to stay off these Cisco forums, my CCNA is about to expire and I haven't hardly used the stuff I learned since I took the exam. However, I am reading these posts, and according to Webmaster:

Webmaster wrote:

It's only a consideration when older systems are in place. I.o.w. on a current Cisco test, always assume the IP subnet zero is enabled 'if' it is not rather obvious based on other hints in the question

Shouldn't the use of the word "classful" be considered one of those obvious hints to NOT use subnet zero, as zero-g-smith points out?

Danman32

Not necessarily. Classful simply means that the base net would be on a class boundary. Most routers would still allow a subnet 0 even if you were using RIP v1.

But still, all official study material I have read so far has stated to assume subnet 0 is to be excluded unless otherwise stated. If you are on a router SIM, then you can use subnet 0 since the IOS will be 12.2 or better, but for form questions that have multiple answers and you are only to select one, and ruling out subnet 0 would eliminate one of the multiple possible answers, logic would say select the other one.

If you can find official indication that you can assume subnet 0 is ok, please cite the reference. Otherwise, all is speculation.

Webmaster

Of course it is speculating. You are creating a discussion about hypothetical case. Cisco won't withhold the information from an exam candidate, there's nothing to 'assume' about IP subnet zero. Anyone who says or writes you should assume something in that hypothetical scenario that does not exist in the real world is speculating. (which besides the point is major part of my job; making speculations about exam content. That doesn't mean I'd just post any speculation without being able to back it up.).

You claim to have read something in official material, but failed to have cited a reference yourself (unless I missed it in another topic). Apart from my speculations about a hypothical scenario, I'm stating facts about the real world, and have quotes from the cisco.com sites and RFCs to support those facts. (see quotes links other topics)

I wrote:

But in that other topic I also already stated that it's a non-issue, because unlike my question the O/P quoted, Cisco won't trick you as in provide a valid answer when subnet zero is enabled and a valid answer for disabled/not supported, without at least a clear hint whether it is enabled.

ExamCram2 wrote:

Cisco tests might be difficult and tricky, but they are fair—they will not withhold information you need to answer the question. The test question will always tell you whether the Zero Subnets Rule is in effect; yes, both types of questions are asked.

www.examcram2.com/articles/article.asp?p=433757&seqNum=6&rl=1

But, let's assume for a sec that ExamCram2 doesn't know what they are talking about, and there is bunch of questions in the CCNA exam which make you assume something about IP subnet-zero. I'm guessing it's not 'official' enough for you, but I'm also sure it will be for most others:

mcmcse wrote:

So which way do you need to learn for the exams? It depends on the exam you are taking. Below we will outline what we know about some of the certifications.
MCSE - While Windows 2000 is RFC 1878 compliant, the MCSE exams will still be testing using the 2N-2 method.
Cisco - With the release of their 2.0 track, they are now testing on the 2N method.
CompTIA - CompTIA exams do not test this in depth so you will probably not run into any questions on their exams that will be affected by this.

www.mcmcse.com/articles/subnetting.shtml
Also notice the heading of the article and link to other article... my good friend Jason and I seem to be on the same line.

Maybe this will do:
Sample chapter of Todd Lammle's CCNA guide from Sybex also happens to be about Subnetting and he's quite clear about it:

http://g.bookpool.com/gp/0504sybex/0782143911.pdf

At least this resulted in some good links I need to add to the FAQ.

Danman32

Anything on Cisco's website about this matter with regard to the exam?