A Subnetting Question (And Answer!)
This past week, I had a customer email me with a binary math question from a website that he couldn't quite figure out how to approach. (I am a big believer in the Non-Disclosure Agreement, and this question was not from a braindump site.) I showed him how to approach the question, and I thought I'd share our work with you. But before you look at the answer and how I got there, why not try the question on your own?
Here is the question:
Assuming four bits have been borrowed for subnets, identify the subnet network addresses. Choose three.
A: 192.168.14.8
B: 192.168.14.16
C: 192.168.14.24
D: 192.168.14.32
E: 192.168.14.148
F: 192.168.14.208
The approach:
You know this is a Class C address, so we've got eight host bits to begin with: 00000000
The question says four bits have been borrowed for subnetting, so we'll put the subnet bits in bold : 00000000
With all subnet bits set to zero, we get this: 192.168.14.0. That's the first network number, but it's not in the list.
Now set the smallest subnet bit to one - 00010000 - we get 192.168.14.16. That's one on the list.
The next smallest subnet bit combination is 00100000 - we get 192.168.14.32. That's two on the list.
The next smallest subnet bit combination is 00110000 - we get 192.168.14.48. You probably notice a pattern here. :) Each subsequent network number is going up by 16 in that last octet. Going up by 16 from here, we get... 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208 --- 208 is the final choice from that list.
The hardest part of solving Cisco's CCNA subnetting questions is having a practiced approach. Believe me, it's not enough to know how to subnet, and you don't have time to figure an approach out in the exam room.
My Binary Math And Subnetting Success Ebook Library has helped CCNAs around the world conquer their binary math anxiety - and as a bonus to you for reading my blog, I'll give you two free days of CCNA Rack Rental time if you order the Binary Math Success Ebook Library within the next 24 hours. Follow the link below to read all about it, and claim your FREE rack rental time!
http://www.thebryantadvantage.com/TheBryantAdvantageMasterySeries.html
Free questions and free rack time. Pretty good deal! :)
To your Cisco success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
This past week, I had a customer email me with a binary math question from a website that he couldn't quite figure out how to approach. (I am a big believer in the Non-Disclosure Agreement, and this question was not from a braindump site.) I showed him how to approach the question, and I thought I'd share our work with you. But before you look at the answer and how I got there, why not try the question on your own?
Here is the question:
Assuming four bits have been borrowed for subnets, identify the subnet network addresses. Choose three.
A: 192.168.14.8
B: 192.168.14.16
C: 192.168.14.24
D: 192.168.14.32
E: 192.168.14.148
F: 192.168.14.208
The approach:
You know this is a Class C address, so we've got eight host bits to begin with: 00000000
The question says four bits have been borrowed for subnetting, so we'll put the subnet bits in bold : 00000000
With all subnet bits set to zero, we get this: 192.168.14.0. That's the first network number, but it's not in the list.
Now set the smallest subnet bit to one - 00010000 - we get 192.168.14.16. That's one on the list.
The next smallest subnet bit combination is 00100000 - we get 192.168.14.32. That's two on the list.
The next smallest subnet bit combination is 00110000 - we get 192.168.14.48. You probably notice a pattern here. :) Each subsequent network number is going up by 16 in that last octet. Going up by 16 from here, we get... 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208 --- 208 is the final choice from that list.
The hardest part of solving Cisco's CCNA subnetting questions is having a practiced approach. Believe me, it's not enough to know how to subnet, and you don't have time to figure an approach out in the exam room.
My Binary Math And Subnetting Success Ebook Library has helped CCNAs around the world conquer their binary math anxiety - and as a bonus to you for reading my blog, I'll give you two free days of CCNA Rack Rental time if you order the Binary Math Success Ebook Library within the next 24 hours. Follow the link below to read all about it, and claim your FREE rack rental time!
http://www.thebryantadvantage.com/TheBryantAdvantageMasterySeries.html
Free questions and free rack time. Pretty good deal! :)
To your Cisco success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
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