MSPress question

Spacer_08

Hello! Please could someone help me on this one. The question can be found on 13-8 of ms press 70-291 (1st edition).

Question:

Your organisation has leased the class c network 199.205.14.0/24. You are subnetting this network using VLSM. Your routers support the zero subnet and the longest match algorithm. You ask one of your support staff to design a subnetting structure but when she submits this you suspect that some of the network/subnet mask allocations are invalid. Which of the following are not valid networks?

A) 199.205.15.64/25
199.205.15.192/26
C) 199.205.15.130/26
D) 199.205.15.96/26
E) 199.205.15.8/27
F) 199.205.15.40/28

I chose A, C, D, E and F. And MS press says only A, C, E are correct. After reviewing their explanation as to why D and F were not correct, it states:

D) Mask = 255.255.255.224
Increment = 256-224 = 32

F) Mask = 255.255.255.248
Increment = 256-248 = 8

This is what stumped me, why does it state the mask is .224 when /26 = 192? And with F why does it state .248 when /28 = 240.

Thanks in advance!

gojericho0

You are correct. That does appear to be an error in the MS book

dynamik

http://support.microsoft.com/kb/830785/en-us

That's listed in the errata.

On page 13-8, the possible answers for objective 1.1 question 2 read:

"A. 199.205.15.64/25
B. 199.205.15.192/26
C. 199.205.15.130/26
D. 199.205.15.96/26
E. 199.205.15.8/27
F. 199.205.15.40/28"

They should read:
"A. 199.205.15.64/25
B. 199.205.15.192/26
C. 199.205.15.130/26
D. 199.205.15.96/27
E. 199.205.15.8/28
F. 199.205.15.40/28"

snadam

yep, and just for the record, it is corrected in v2. The questions dont start until 13-11. It threw me off until I realized OP was using v1

dynamik

snadam wrote:

It threw me off until I realized OP was using v1

You better work on your reading comprehension skills or those MS tests are going to eat you alive

I just ran over it, and the changes in the errata make D correct, but F is still wrong. Looks like they forgot to change F to /29

/25
0
128

/26
0
64
128
192

/27
0
32
64
96
128
160
192
224

/28
0
16
32
48
64
80
96
112
128
144
160
176
192
208
224
240

snadam

dynamik wrote:

snadam wrote:

It threw me off until I realized OP was using v1

You better work on your reading comprehension skills or those MS tests are going to eat you alive

thats why I read the questions twice over!

Spacer_08

Thanks very much guys. And thanks for the link dynamik, I think i'll spend more time reading that than the books themselves! And yes, it appears F is still wrong on the corrections list