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Subnet Zero and the All-Ones Subnet

In context of Cisco Certification tests, what is your opinion if a question uses slash notation when asking the number of useable subnets? Does this imply that a test-taker should use 2**n (classless) instead of 2**n-2 (classful) as the formula to figure out the number of subnets?

Wendell Odom, who writes for Cisco Press, states that Cisco makes no public statement on which formula to use when there are no hints in the question to determine the number of useable subnets. In his opinion, if the question does not imply anything on which formula to use, you should use the classful formula of 2**n-2 when determining the number of useable subnets.

So the question remains, when a test question uses slash notation, does this 'imply' that we need to use the classless formula?

1 REPLY
Purple

Re: Subnet Zero and the All-Ones Subnet

Hi,

The last time I checked, the official Cisco course notes for the CCNA exam still stated that the answer was 2^n-2. So that's what I would go with.

Paresh

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