quick question about something in Sybex CCNA 5th edition

JNeko

Hi everyone!
I'm new here, so be easy on me. Just started my CCNA studies, it's coming along good...just very very slowly if you know what I mean. I am coming from almost no background in networking, but I really do enjoy this (even if I still suck at it now)!

I have a question regarding something I read in the Sybex CCNA 5th edition:

on pg 124 you will find something like this:

So, what private IP address should I use? (topic title)

That’s a really great question: Should you use Class A, Class B, or even Class C private
addressing when setting up your network? Let’s take Acme Corporation in San Francisco as
an example. This company is moving into a new building and needs a whole new network
(what a treat this is!). They have 14 departments, with about 70 users in each. You could probably
squeeze one or two Class C addresses to use, or maybe you could use a Class B, or even a
Class A, just for fun.
The rule of thumb in the consulting world is, when you’re setting up a corporate network—
regardless of how small it is—you should use a Class A network address because it gives
you the most flexibility and growth options. For example, if you used the 10.0.0.0 network
address with a /24 mask, then you’d have 65,536 networks, each with 254 hosts. Lots of
room for growth with that network!
But if you’re setting up a home network, you’d opt for a Class C address because it is the easiest
for people to understand and configure. Using the default Class C mask gives you one network
with 254 hosts—plenty for a home network.
With the Acme Corporation, a nice 10.1.x.0 with a /24 mask (the x is the subnet for each department)
makes this easy to design, install, and troubleshoot.

My question: can you please explain to me just how a Class A 10.0.0.0 network address with a /24 mask can yield 65,536 networks, each with 254 hosts? Is a Class A address not network.node.node.node? If so, then should it not be just the opposite? that is yielding lots and lots of host on one network?

Sorry for this boring question, I am sure I am just missing something simple here.

Thank you!

Jared

GeorgeMcFly22

Normally network 10.0.0.0 use 255.0.0.0 or /8 as subnet-mask, or like you say network.node.node.node
This would give you 1 network with :
2power24(3x8bits) min 2 (network and broadcast ip) = 16777214 hosts

Thats why they burried 16 bits from the node portion and make it network portion (this is called subnetting)
This gives us 10.0.0.0 with 255.255.255.0 or /24 or network.network.network.node
This makes 2power16(bits burried) = 65536 networks
and 2power8(bits over) min 2 = 254 hosts