# Who knows how to subnet? Solve this puzzle >.<

This question came up on a practice exam....

Which of the following network addresses enable you to support a network consisting of 60 subnets with up to 300 hosts on each subnet? (choose all that apply)

A. 10.48.0.0/14

B. 192.168.98.0/24

C. 172.30.0.0/25

D. 10.236.128.0/21
WIP: can't decide.

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Well you'll need 6 bits for the subnets (64 subnets) and 9 bits for the hosts (510 hosts).

Therefore, you'll 15 bits total. There's only one that satisfies that.
• Exactly what I was thinking!

I gave only one answer ...

Either I been studying too much lately and my brain is getting fried or something is wrong.
WIP: can't decide.
• I haven't subnetted for a while, but isn't (A) and (D) the correct answer?
Aren't (B) and (C) wrong because they only allow 256(-2) and 128(-2) hosts per subnet?

(A) and (D) have enough (6 and 13) bits for subnets and enough (18 and 11) bits for hosts?
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I see what you guys did, but they're not using the standard class masks. If you're given 10.236.128.0/21 to use, you only have 11 bits to work with.
• dynamik wrote:
I see what you guys did, but they're not using the standard class masks.
It depends on the interpretation of what's given (this question is very vague and I may not be correct). Your assumption could be correct if the question was something like:
"Your department is given a 10.236.128.0/21 network segment [meaning you only have this segment and, therefore, have to FURTHER subnet it into subnets/hosts]."

The actual question asks us which subnets could be a PART OF an original network address that was, at some point, subnetted into answer(A) or answer(D).
What I mean is if my math teacher gives me 2*X=Y+2 and wants me to find X, I should find X, not Y.

dynamik wrote:
If you're given 10.236.128.0/21 to use, you only have 11 bits to work with.
11 bits to work with hosts.
Since the range for private 10-dot network is 10.x.x.x, you can use any amount of bits from all octets except first 8 and last 11 bits. So, 21 - 8 = 13 bits for subnets.
10.0.0.0 /21 First subnet
10.0.8.0 /21
10.0.16.0 /21
10.236.128.0 /21 Given subnet
10.255.248.0 .21 Last subnet
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