CCENT Pratice Test question confustion

If a device is assigned the IP address 9.80.86.211 /27 on an interface, the valid subnet address for the interface will be ____________

So a /24 address is 255.255.255.0, this leave you with 3 bits (27-24=3), that's 128+64+32=224. The subnet address should be 255.255.225.224,

a) 9.80.86.192
b) 9.80.86.223
c) 9.80.86.224
d) 9.80.86.128

There's the answers they give, so I say the answer is C, Practice Test says no A is the correct answer, what am I missing?

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Comments

clarson

The question would have been more appropriate to have asked "the network address of the interface". Which, of course, is 9.80.86.192.

As you pointed out, the subnet address is /27 or 255.255.255.224. But, those aren't valid answers to the question. So, from the answers given, you'd have to determine that they are asking for the network address of the interface.

Not a very fair question if you ask me.

PCTechLinc

9.80.86.211/27

/27 means that your subnet mask is 255.255.255.224, which you correctly state above. If we take 256 and subtract 224, we get 32. 32 is your "Magic Number", or your subnet range. Start at 0 in the octet where the last bit is "borrowed", then keep adding 32 until you find the subnet that 211 is higher than, but doesn't go to the next. So we get:

0
32
64
96
128
160
192
224

224 is too high (next network), so your valid range would be:

9.80.86.192 = Network
9.80.86.193 = First valid host
9.80.86.222 = Last valid host
9.80.86.223 = Broadcast

They are asking "valid subnet address for the interface" which is badly worded, but since you can't assign a subnet address to an interface, A is the correct answer. Hope that helps it make a bit more sense.

TechGromit

Thanks for the clarification. Can anyone give advise on what my scores on practice exams should be to know if I'm ready to take the exam?

PCTechLinc

In my experience, it really depends on the quality of the practice exams. How closely does the practice exam mimic the real environment? When I was studying ICND1, my school had a subscription to uCertify, and it was fairly close. More recently, in studying for the CCNA Security (210-260), I had a subscription to Boson, and I'd have to say that was the best. I found the Boson to be extremely close to the real exam, and I wouldn't have passed if not going through those.

In general, regardless of which practice exam vendor you choose, you want to score at least 90% consistently, and understand WHY each question is correct or not. I will usually take a practice test in practice mode (I get as much time as I want), and go through ALL the questions. It will usually take me a couple hours, but it helps me to evaluate each question in its entirety, and it also helps me sit down and focus on the exam without taking a break. That helps with the exams that have a very long time limit.

Once I've gone through that, I will take a few practice exams in simulated mode with time limits and random questions, and see how I fare. Hopefully you can knock this one out and move on to finish CCNA. Best of luck!

WastedHat

subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online is really uesful for practicing

I wouldn't say its bad wording. On that site it would be phrased "what subnet does 9.80.86.211 belong to?", in the question you had it's asking what the subnet address is which is the same thing.

You were on the right track calculating the subnet mask. The next step is to notice the 255.255.255.224 subnet mask means all the subnet address's will will be multiples of 32 in the last octet. Then you just find what multiple of 32 includes 211 (from the last octet of the IP address).

The answer is 9.80.86.192 because you multiply 32 until you reach the subnet that contains 211.