I'm independently studying Cisco with CBT Nuggets. I'm having some issues grasping subnetting when it comes to Class A in one of the reviews.

I'll share a couple of expamples, followed by some questions.

A) 10.25.66.15.4/23

Mask 255.255.254.0 (correct?)

B) 63.24.89.21/18

Mask 255.255.192.0 (correct?)

Why does example A have 15 subnet bits and not 7 subnet bits combining bits of octet 3 and 4? (Because there are only 7 bits in 254, right?)

Why does example B have 10 subnet bits and not 2 subnet bits combining bits of octet 3 and 4? (Because there are only 2 bits in 192 right?)

Last, are these both basically considered Class A because first octet for the network address is lower than 172 (class B)?

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