Subnetting Drills: Find the Subnet ID

 In CCENT-OLD, IPv4 Ch. 14 Address Drills

Since this week’s question requires that you do some sub netting math, it seemed like a good time to toss out some sub netting practice questions. I plan to add a techie topic video about how to find these subnet IDs without using binary math, but in the mean time, here’s the practice. The focus is on finding the subnet ID, not so much what a subnet ID is and what it’s used for. Post queries if you have them!!

Find the subnet ID of the following:

10.4.77.99, 255.255.0.0

10.4.77.99, 255.255.255.0

172.30.201.199, 255.255.255.0

10.4.77.99, 255.255.240.0

10.4.77.99, 255.255.255.224

172.30.201.199, 255.255.255.248

192.168.1.199, 255.255.255.248

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Answer to Monday's Subnetting Speed Test Question
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Max

AS far as I have done this the subnet ID’s are as follows

Questions Solution
10.4.77.99, 255.255.0.0 – 10.4.0.0

10.4.77.99, 255.255.255.0 – 10.4.77.0

172.30.201.199, 255.255.255.0 – 172.30.201.0

10.4.77.99, 255.255.240.0 – 10.4.64.0

10.4.77.99, 255.255.255.224 – 10.4.77.96

172.30.201.199, 255.255.255.248 – 172.30.201.192

192.168.1.199, 255.255.255.248 – 192.168.1.192

lyjo

@Max –
Thanks for the post. All are correct!
@All –
A rhetorical question – are you ready to get these answers within your time goal?
And another subnet question – were any of these subnet broadcast addresses?
Wendell

Dan

10.4.77.99, 255.255.0.0
10.4.0.0 10.4.0.1 – 10.4.255.254 Broadcast 10.4.255.255

10.4.77.99, 255.255.255.0
10.4.77.0 10.4.77.1 – 10.4.77.254 Broadcast 10.4.77.255

172.30.201.199, 255.255.255.0
172.30.201.0 172.30.201.1 – 172.30.201.254 Broadcast 172.30.201.255

10.4.77.99, 255.255.240.0
10.4.76.0 10.4.76.1 – 10.4.91.254 Broadcast 10.4.91.255

10.4.77.99, 255.255.255.224
10.4.77.64 10.4.77.65 – 10.4.77.94 Broadcast 10.4.77.95

172.30.201.199, 255.255.255.248
172.30.201.192 172.30.201.193 – 172.30.201.198 Broadcast 172.30.201.199

192.168.1.199, 255.255.255.248
192.168.1.192 192.168.1.193 – 192.168.1.198 Broadcast 192.168.1.199

lyjo

Hi Dan,
I like them all, except the 4th one… I’m confident you’ll see the mistake once you re-look. Thanks for the post!
Wendell

Mirek

I’m not confident about the 5th one either.
Problem IP Address Mask Subnet ID Broadcast Adress First IP Last IP
10.4.77.99, 255.255.0.0 10.4.0.0 10.4.255.255 10.4.0.1 10.4.255.254
10.4.77.99, 255.255.255.0 10.4.77.0 10.4.77.255 10.4.77.1 10.4.77.254
172.30.201.199, 255.255.255.0 172.30.201.0 172.30.201.255 172.30.201.1 172.30.201.254
10.4.77.99, 255.255.240.0 10.4.64.0 10.4.79.255 10.4.64.1 10.4.79.254
10.4.77.99, 255.255.255.224 10.4.77.96 10.4.77.127 10.4.77.97 10.4.77.126
172.30.201.199, 255.255.255.248 172.30.201.192 172.30.201.199 172.30.201.193 172.30.201.198
192.168.1.199, 255.255.255.248 192.168.1.192 192.168.1.199 192.168.1.193 192.168.1.198

lyjo

Mirek – correct all around!
Wendell

[…] Monday’s question was about interpreting the output of two show commands, show ip route and show ip interface brief. Answers are below the fold. Enjoy! […]

Anna

Hi Wendell,

I watched different tutorials on subnetting, learned some bits and pieces but your book laid out all the rules which made me feel comfortable on this topic.

Thanks,
Anna

Bav

I am now at the point where I can do them in my head in under 10 seconds. Is that good for the exam?

lyjo

Hi Bav,
Yep, I’d say 10 seconds is plenty fast!
Wendell

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