# Teacher has me confused; Am I over thinking this problem?

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Im taking a networking class and my teacher returned my test with one of my question wrong with zero credit, however I think I had the question correct. He is currently looking over it to see if I will get any credit for the problem.

Here is the problem I got no credit for.
1. You design a network for a customer, and the customer insists that you use the same subnet mask on every subnet. The customer will use network 10.0.0.0 and needs 200 subnets, each with 200 hosts maximum.
a. What subnet mask would you use to allow the largest amount of growth in subnets?

b. Which mask would you work and would allow for the most growth in the number of hosts per subnet.

I looked at another student paper that got it correct and he had " 255.255.255.0 " for part A
and "255.255.0.0 "

Here is what put summarized..

The customer had put a range on the subnets ( at least 200) and a limit on the hosts ( max of 200).

Part A

Asked to max out subnets, therefore I used 255.255.255.252 which was 4.19 x 10^6 subnets with 2 hosts per subnet. The customer said a max of 200 hosts so 2 hosts per subnet was with in the max of 200 hosts.

Part B

Asked to max out hosts, therefore I used 255.255.255.128 which was 2^7 - 2 = 126 hosts per subnet which meet the 200 hosts per subnet max set by the customer. And meet the 200 subnets min.

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a) largest amount of growth in subnets

255.255.255.0 /24

11111111.11111111.11111111.00000000

subnets: 65,536 & hosts: 254

b) most growth in the number of hosts per subnet

255.255.0.0 /16
11111111.11111111.00000000.00000000

256 total subnets & 65,534 hosts

The wording is tricky as it states "the customer insists that you use the same mask on every subnet". Implying it might be after a single answer. In which case of the two a /16 Is likely the one I'd go with if only one mask. Even though the number of hosts per subnet is huge. Hopefully your teacher will clarify things
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HappyFeet wrote: »
1. You design a network for a customer, and the customer insists that you use the same subnet mask on every subnet. The customer will use network 10.0.0.0 and needs 200 subnets, each with 200 hosts maximum.
a. What subnet mask would you use to allow the largest amount of growth in subnets?
b. Which mask would you work and would allow for the most growth in the number of hosts per subnet.

(a) 255.255.255.0 allows the most subnet growth: over 65000 subnets and over 250 hosts.
(b) 255.255.0.0 allows the most subnet growth: over 250 subnets and over 65000 hosts.
Asked to max out subnets, therefore I used 255.255.255.252 which was 4.19 x 10^6 subnets with 2 hosts per subnet. The customer said a max of 200 hosts so 2 hosts per subnet was with in the max of 200 hosts.

Asked to max out hosts, therefore I used 255.255.255.128 which was 2^7 - 2 = 126 hosts per subnet which meet the 200 hosts per subnet max set by the customer. And meet the 200 subnets min.

Maximum - The greatest quantity or degree reached or recorded; the upper limit of variation.

By definition, the maximum amount must be attainable. Your answers which only allow 2 or 126 hosts per subnet are wrong.
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Remember, you always have to meet the max requirements for both subnets and hosts.
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CCENT: 04/16/2012
CCNA: TBD
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