I don't get this question

Hi all,
Studying sub-netting. Got all questions right but this one. It is from Todd Lammle's book CCNA 5th Edition.

Anyway the question is:

11. Which of the following IP addresses fall into the CIDR block of 110.68.4.0/18?
A. 110.68.8.32
B. 110.68.7.64
C. 110.67.6.255
D. 110.66.3.254
E. 110.65.5.128
F. 110.64.12.128

The answer for this is something like this...

B, C, E.

A Class A network address with a /18 is 255.255.192.0. The subnets in the third octet are 0, 64, 128, 192. The network address in the question is 110.64.0.0, with a broadcast of 110.64.127.255, since the next subnet is 110.64.128.0. Answers B, C, and E are correct host IDs.

I agree with the subnetwork address of 110.64.128.0, the valid host range is from:
110.68.0.1 - 110.68.127.254 and the broadcast is 110.68.127.255.

Given the above valid host ranges I chose A & B as C, D, E, F fall outside the valid host range for the subnet, yet the book states that the correct answer is B, C, E. I need to know where I went wrong...

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Comments

networker050184

You have 18 bits for network. That puts the range from 110.168.4.0 - 110.168.7.255. You borrowed 2 bits (frrom the third octet) that increments by 4 so the networks would be 110.168.0.0 110.168.4.0 110.168.8.0 and so on. Hope this helps. If you need more clarification let me know.

steveo1985

that question doesn't appear in my 5th edition, I have one similar though..... how could the answers be C and E? /18 is a class B address and has two network parts i.e 110.168. and two host parts i.e 8.32

The question in my book that is similar is
which of the following IP addresses fall into the CIDR block of 110.68.4.0/22 (choose three)
A. 110.68.8.32
B. 110.68.7.64
C. 110.68.6.255
D. 110.68.3.254
E. 110.168.5.128
F. 110.68.12.128

As networker050184 said the range is 110.168.4.0 - 110.168.7.255 and the answers are B, C, E

hope that clears it up :P

r_durant

Ashley_101 wrote:

Hi all,
Studying sub-netting. Got all questions right but this one. It is from Todd Lammle's book CCNA 5th Edition.

Anyway the question is:

11. Which of the following IP addresses fall into the CIDR block of 110.68.4.0/18?
A. 110.68.8.32
B. 110.68.7.64
C. 110.67.6.255
D. 110.66.3.254
E. 110.65.5.128
F. 110.64.12.128

The answer for this is something like this...

B, C, E.

A Class A network address with a /18 is 255.255.192.0. The subnets in the third octet are 0, 64, 128, 192. The network address in the question is 110.64.0.0, with a broadcast of 110.64.127.255, since the next subnet is 110.64.128.0. Answers B, C, and E are correct host IDs.

I agree with the subnetwork address of 110.64.128.0, the valid host range is from:
110.68.0.1 - 110.68.127.254 and the broadcast is 110.68.127.255.

Given the above valid host ranges I chose A & B as C, D, E, F fall outside the valid host range for the subnet, yet the book states that the correct answer is B, C, E. I need to know where I went wrong...

Ashley,
You're not wrong, the question is incorrect in your edition of the book...Steve has the right question...
Have a look at this post, it has the errata for that question...
http://www.techexams.net/forums/viewtopic.php?t=25086

networker050184

It is still a class A address. This is just the CIDR block it doesn't change the address class range.

steveo1985

Also networker050184 where you going by the /18 or the /22? as /22 has a block size of 4 and /18 is 64 if subnet zero was on then it would it be 110.168.0.0 - 110.168.63.255? for the /18 CIDR?

Is that correct? so /18 1st would be 110.168.64.0 - 110.168.127.255 so if the question Ashley_101 had based on the /18 then none of those answers given to him where correct.

steveo1985

Yes sorry your correct :P its in the 1-127 range for class A. Sorry my mistake.

NeonNoodle

Ashley_101 wrote:

Hi all,
Studying sub-netting. Got all questions right but this one. It is from Todd Lammle's book CCNA 5th Edition.

Anyway the question is:

11. Which of the following IP addresses fall into the CIDR block of 110.68.4.0/18?
A. 110.68.8.32
B. 110.68.7.64
C. 110.67.6.255
D. 110.66.3.254
E. 110.65.5.128
F. 110.64.12.128

The answer for this is something like this...

B, C, E.

A Class A network address with a /18 is 255.255.192.0. The subnets in the third octet are 0, 64, 128, 192. The network address in the question is 110.64.0.0, with a broadcast of 110.64.127.255, since the next subnet is 110.64.128.0. Answers B, C, and E are correct host IDs.

I agree with the subnetwork address of 110.64.128.0, the valid host range is from:
110.68.0.1 - 110.68.127.254 and the broadcast is 110.68.127.255.

Given the above valid host ranges I chose A & B as C, D, E, F fall outside the valid host range for the subnet, yet the book states that the correct answer is B, C, E. I need to know where I went wrong...

The address 110.68.4.0/18 falls in the range of 110.68.0.0-110.68.63.255

110.68.0.0 is the subnet address and 110.68.255.255 is the broadcast address.

Anyway the answers are A and B.

Look at it from a binary point of view.
01101110.01000100.00000100.00000000 = 110.68.4.0
with a prefix of 18 we have
01101110.01000100.00000100.00000000

So the subnet address is
01101110.01000100.00000000.00000000 = 110.68.0.0

and the broadcast address is
01101110.01000100.00111111.11111111 = 110.68.63.255

networker050184

As the name says its CLASSLESS you don't need to go by the address class when using CIDR from the way I was told. This isn't a subnet it is a CIDR block.

steveo1985

Again yes lol :P

networker050184

Well, I guess I was taught wrong. I decided to use my solarwinds cidr calculator to see the results are 110.168.0.1 - 110.168.63.255 for the /18. Learn something new on here everyday!

steveo1985

same, Im still learning all the time. This forum is good because it make you question things.

networker050184

Yeah this is the best forum I have found. People are here to help people not bash them which helps people learn.

mgeorge

Welcome to the community Ashley

, I would answer ya question but it look as if several people have beat me to it, also keep in mind Cisco is retiring the current exam on Nov. 6th, 2007 so therefore you may want to look into new study materials for the upcomming objectives if your not going to sit the exam before the retire date. The new exam id is 640-802

The Sybex CCNA 6th edition is due out aug 15th. Google is mans new best friend...

Any who, time for this engineering slave to get back to work

gabrielbtoledo

For one moment I thought I didn't know subnet.