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Youngearth

Seeking answer to this CCNA practice test question

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I'm studying for my CCNA and finding practice questions online to study. I've come across this question on several, and I'm getting different answers for it. Here it is:

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An office has 8 floors with approximately 30-40 users per floor. What command must be configured on the router switched virtual interface to use address space efficiently?

A. ip address 192.168.0.0 255.255.0.0
B. ip address 192.168.0.0 255.255.254.0
C. ip address 192.168.0.0 255.255.255.128
D. ip address 192.168.0.0 255.255.255.224

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Some sites say B and some say C. I thought it would be B, since 8 x 40 gives 320 possible users, hence a /23 IP address (in answer B). Why would a /25 be the answer (in answer C?)

Edited by Youngearth

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I agree, B is the right answer. The key is switched virtual interface, meaning 1 VLAN. B will give you that with 512 IP addresses. 

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It will never be C or D Since you need to factor in expansion even though they don't ask right now.

For now, A is too much as a /16

B is optimal for the amount catering to 320 people, as that / notation gives you 510 usable addresses

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Ok, that's what I thought, too. I have no idea why some sites listed "C" as the answer.

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maybe they were thinking C since its /25...or 62 usable hosts, anything less is 30 hosts which is too small as you need 40

 

anyway I need to revise whats a SVI haha

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This isn't the first time I've run across wrong answers in practice tests online. I guess it's a good way to keep me on my toes and to think for myself.

Btw, if I wanted to contact a specific user on the forum, is the "message" feature the only way to do that? There's no email option?

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I'm no Cisco expert, but C is the correct answer. Cisco actual question would not be this vague. Someone else tried to recreate a Cisco question and left out some details. Cisco's idea of subnetting involves different parts of a networks distinguishable by, ie: departments, buildings, floors, geological locations. In this question they want you to divide your entire network by floors. Each floor would have it's own network consisting 30 to 40 devices. How would you divide this network's IP into efficient use of the IPs.

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