Subnetting Question??

First, let me introduce myself

:

I'm a proud guest of Tech Exams site, I feel like I'm sorrounded by the best IT guys in the world when I come here. I actually was encouraged by a couple of your posts to take the CCNA after passing the Network+ and A+ exams.

................ Thanks to the Founder of Tech Exams your your website, you are appreciated!......

Okay now that we've met, heres my question;

On page 142 of the CCNA 640-802 six edition sybex book is a network. I'm confused as to how VLSM (or Subnetting, if both means the same thing works). The impression that I'm getting is that for an entire network of routers and switches you can only use one class. Is this true?

I thought class A, B, and C all can communicate once you have a router. I know they can't if you have switches of cource?

Can you clarify this for me please?

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Comments

flipmad

VLSM is used in the event your are using CLASSLESS routing. This means you are using different subnets.

Classfull routing is when all of your networks communicate on the same subnet mask.

TMM3

If you think about it VLSM (Variable Length Subnet Mask) means that the subnet mask can be of varying length and doesn't have to be fixed to the class. Hence you can subnet.
Yes, you need a router or Layer 3 switch to communicate between different subnets or classes of ip addresses.

GPU

What I'm really trying to ask is, can you use different class addresses in a network?

And if you can, why do you need to subnet?

networker050184

Yes you can use different classes in a network.

If you didn't subnet you would waste tons of addresses. For example on a point to point link you only need two addresses. If you use a whole class C network you are just wasting the rest of the addresses.

GPU

Can you give me a practical example of why I need to subnet even though there are other classes. I now know how to subnet after doing the tutorials. But now I see it as even being more worthless.

Let me put it this way, if I was a CCNA tech and you were the CCNP Network Admin, what would and could you tell me to show me what's subnetting for and why is it so important.

Help me please, I just want to be educated, that's why I'm here.

dtlokee

Would it make sense to assign 16,777,214 host addresses to a VLAN with 100 computers?

That is what would happen if you tried to use a class A address without subnetting.

We subnet to make a large address space into smaller parts for each broadcast domain. The routers are responsible for moving packets to the destionation based on the subnet address.

this won't work:

10.0.0.0/8 --- Router1 ---- 10.0.0.0/8

you need to break up the single 10.0.0.0/8 into smaller parts (in this case atleast 2)

so you could do:

10.0.0.0/9 ---- Router1

10.128.0.0/9

that would give you 2 subnets with roughly 8.5 million possible hosts on each (2**23-2)

if you need more subnets you will borrow the number of bits needed based on the formula of 2**s where s is the number of bits borrowed.

so if you borrow 1 bit it makes 2 subnets, 2 bits will give you 4 subnets, 3 bits will be 8 subnets...

GPU

Thanks,
And I really appreciate not just a CCNA or a CCNP but a 'CCIE' fully answering my question.

So basically (using a router of course), since we are subnetting, only the nodes on that particular network can see each other and communicate, unless we make a route to another network right?

So it just makes it more secure, and more manageable because you know were everyone is. And it allows for more departments.

Eg (bare with me):

A. 11.0.0.1-11.255.255.255 /8 for Walmart
One big network, no subnetting

B.
11.0.0.1-11.31.255.255 /11 for Walmart Main Office
11.32.0.1-11.63.255.255 /11 for Walmart Home and Office
11.64.0.1-11.95.255.255 /11 for Walmart Auto
11.96.0.1-11.127.255.255 /11 for Walmart Groceries
11.128.0.1-11.159.255.255 /11 for Walmart Clothes
Multiple Networks (Multiple Departments for Walmart)
Easy to managing security, troubleshooting and enjoying more broadcasts (meaning faster network).

Am I Right?

networker050184

You have the idea of it down. I don't think any department would need that many addresses still though

ITdude

GPU wrote:

Thanks,
And I really appreciate not just a CCNA or a CCNP but a 'CCIE' fully answering my question.

Hmm, I wonder what he meant by that?