Possible error in 200-125 Sybex book.

I was running through all the chapters last night and taking the quizzes at the end. I came to the subnetting portion and got stumped.

The question is: The network address of 172.16.0.0/19 provides how many subnets and hosts?

The way I work this out is the following:

The next boundary is 24. So 24-19 = 5. 2^5=32. That's our block size.

172.16.0.1 is our first subnet
172.16.32.1
172.16.64.1
etc

Now, to actually answer the question. How many hosts? Well, we have 13 host bits from a /19. So 2^13=8192. Minus the network and broadcast = 8190 hosts.

For the number of subnets, we have 3 subnet bits from the /19. So 2^3=8.

In the Sybex book is has 7 subnets, 8190 hosts. Am I correct or am I wrong? If I'm wrong, please correct me.

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Comments

WastedHat

I calculated it the same as you. 3 subnet bits and 13 host bits = 8 and 8190.

Unless it says something about not including the zero subnet it must be an error, I've found quite a few in the ICND2 part.

MAC_Addy

I'm thinking that subnet zero can play a part, but then again it'll be first and last subnet not used, so 6 subnets. I think it's just an error in the book. It was driving me absolutely crazy last night. I had a moment to where I was saying to myself "I don't think I know subnetting anymore!". But I went on to the other questions and got all them correct. I did look for errata for this book, but it appears it's not out for this version, yet.

WastedHat

Ha I've had quite a few moment like that. Did you always use a subnet calculator after you got CCNA?

MAC_Addy

Honestly I've done it by hand most of the time. It's not that often that I have to create new subnets. And if I do for work, it's usually a /24. I am re-taking the CCNA exam on Friday since mine has expired and I'm wanting to take the CCNP.

WastedHat

Nice good luck. When you recertify do sit the full composite exam? or is there a special version just for recertifying?

MAC_Addy

Thanks. There's no special just. You can either go the two test route or take the composite. I'm taking the composite since I have been working with Cisco networks for quite some time. For me, it was merely reading the latest book and understanding some of the little things again. Fingers crossed I pass!

OctalDump

WastedHat wrote: »

Nice good luck. When you recertify do sit the full composite exam? or is there a special version just for recertifying?

In this case, since the CCNA is expired then you need to resit the exams as normal. If they hadn't expired and you just needed to renew, then you could sit just the ICDN2 or any CCNA level exam in the other streams, or any CCNP level exam. Cisco is good for collecting certifications and renewing, but terrible once they expire.

To the actual question, I don't think this type of question is on the CCNA exams. Typically it will be more along the lines of "you have this topology with these p2p links and these networks which need to support this number of hosts". And I'm 99.99% sure that the zero subnet never comes up (it's basically deprecated for 20+ years).