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Hello guys,

I've ran into a CCNA question that's giving me a headache and I hope you can help me figure this out.

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I have to include the following interfaces in my OSPF

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E0 192.168.12.65

S1 192.168.12.125

S2 192.168.12.121

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While leaving out the interfaces

E1 192.168.12.129

S0 192.168.12.187.

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Possible option are

A) #network 192.168.12.64 0.0.0.127 area 0

B) #network 192.168.12.64 0.0.0.63 area 0

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and 3 more that I won't include because they are obviously wrong and not worth considering.

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I did my math and I chose A, but the test says that the right answer is B because with a 0.0.0.127 I would have a range from 192.168.12.64 to 192.168.12.191, including interfaces I don't want in my OSPF.

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I tried to calculate network ranges over and over but I'm just getting lost, I'm not getting the same results and from what I did, option A looks fine to o.

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For sure I'm being dumb and I'm missing some obvious details.

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Can someone give me a step by step procedure of the solution of this question?

I thought I was very good with network range and subnet calculation...

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Please help me out guys, my head is exploding :)

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Thanks a lot!

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Ciao

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