70-410 question assistance?

flitter

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Can anyone assist with this 70-410 question taken from aiotestkin, why should it not be A?

Which command should you run?
Posted on:Tuesday, Oct 20, 15
Your company has a main office and four branch offices. The main office contains a server named
Server1 that runs Windows Server 2012 R2. The IP configuration of each office is configured as
shown in the following table.




You need to add a single static route on Server1 to ensure that Server1 can communicate with the
hosts on all of the subnets.
Which command should you run?

A.
route.exe add -p 192.168.0.0 mask 255.255.248.0 172.31.255.254

B.
route.exe add -p 192.168.12.0 mask 255.255.252.0 172.31.255.254

C.
route.exe add -p 192.168.8.0 mask 255.255.252.0 172.31.255.254

D.
route.exe add -p 192.168.12.0 mask 255.255.255.0 172.31.255.254

Ans: B
 
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signumfidei

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Answer A will not communicate to any branch offices due to the subnet mask.
Answer C will only communicate with Branch1 & 2
Answer D will only communicate with Branch1
 

gluemaker

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Actually B makes the most sense.

A has the Subnet at 255.255.248.0 or /21 meaning 2048 possible hosts (minus 1 address for network address and 1 address for the broadcast). That means it will span from 192.168.0.0 - 192.168.7.255 so that will not cover our branch offices.
B has the subnet at 255.255.252.0 or /22 meaning 1024 possible hosts(minus 1 address for network address and 1 address for the broadcast). That means it will span from 192.168.12.0-192.168.15.255 so that WILL cover our branch offices.
C has the same subnet as B and the same number of hosts (1024)(minus 1 address for network address and 1 address for the broadcast) but the IP addressing starts at 192.168.8.0 meaning our last address will be 192.168.11.255 which is just before our first branch office.
D has a standard class C 255.255.255.0 or /24 meaning 256 hosts so the address range would be 192.168.12.0-192.168.12.255 which only covers Branch 1.

Hope this helps! If you feel like you need some subnetting help, let me know and I'll be glad to assist.
 
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