Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Community Member

Adding one VLSM subnet to an existing design

Hello there!

I'm studying for my CCENT exam and this practice question in the book keeps tripping me up.  I'm starting to think that it's a typo.  

The problem is regarding adding one subnet to an existing design.  The existing design already has these five subnets:

10.0.0.0/24

10.0.1.0/25

10.0.2.0/26

10.0.3.0/27

10.0.6.0/28

The boss cannot decide among five competing subnet masks to use for this next new subnet to add to the internetwork.  However, the boss wants you to practice VLSM and plan the subnet ID that he would use for each of those four possible masks.  He tells you that the new subnet ID must be part of Class A network 10.0.0.0, that the new subnet must not overlap with the original five subnets, and that the new subnet ID must be the numerically lowest possible subnet ID (without breaking the other rules).  Pick the one subnet ID that you would plan to use based on the following mask.

/22

The answer guide says it is 10.0.8.0/22 as the numerically lowest new subnet number that does not overlap with the existing subnets.  However; this is confusing to me as it seems like the correct answer should be 10.0.4.0/22, since it is not overlapped with any of the existing subnets and is a lower subnet than 10.0.8.0/22.  

Let me know if you need clarification on this.  Thank you all!

Everyone's tags (1)
1 ACCEPTED SOLUTION

Accepted Solutions
VIP Purple

10.0.4.0/22 includes:

10.0.4.0/22 includes:

  • 10.0.4.0/24
  • 10.0.5.0/24
  • 10.0.6.0/24
  • 10.0.7.0/24

Which overlaps with 10.0.6.0/28.

2 REPLIES
VIP Purple

10.0.4.0/22 includes:

10.0.4.0/22 includes:

  • 10.0.4.0/24
  • 10.0.5.0/24
  • 10.0.6.0/24
  • 10.0.7.0/24

Which overlaps with 10.0.6.0/28.

Community Member

Hi Philip,

Hi Philip,

But from my calculations when listing out the subnet number's I get the following:

255.255.252.0   (256 - 252 = 4)

10.0.0.0.

10.0.4.0

10.0.8.0

What could I be missing? 

Thank you!

298
Views
0
Helpful
2
Replies
CreatePlease to create content