Why Subetting!!??

Hi! ppl

I know this is really a stupid question to ask but i want to get everything off my mind before i step into a wonderful palce called Cisco Land so here it does. what is the basic concept of subnetting : why do we need to do it and where is it applied applied : :oops:

Basically, it is to segment your network for various reasons, such as security and limit broadcast. For example, you might have 3 departments at work: marketing, sales and accounting. You may want to segment your network into 3 subnets, one for each department.

This will make your network more manageable and efficient, especially, if you have a lot of hosts. Segmenting by department or use is a common way of doing this.

There is a good discussion of subnetting under the Networking/General/Subnetting menu.

Hope this is what you are looking for.

ok cool
another thing i wanted to know was, what is the maximum and the minimum number of subnets and can be accomidated in Class C and the maximum and minimum number of hosts in the above said subnetwork? thanx

Ok lets jump straight in !
Well first off, possible class C subnet masks for the 4th octet are listed below
(example 255.255.255.192 or 255.255.255.254)

MASK BITS
192 = 2
224 = 3
240 = 4
248 = 5
252 = 6
254 = 7

Now the formula for number of subnets is
(2 ^ n) - 2 where n is the BITS column above
so if we take 224 then

(2 ^ 3) - 2 = 6 subnets

now you get the number of hosts by subtracting the number of BITS from the total bits in the octet which is 8 so subtract 8 -2 = 6
you have 6 bits for the host ID.. the formula for number of hosts is the same as above, just change the value of n to 6.. so..

(2 ^ 5) - 2 = 30 hosts

you can calculate those values for all the above masks

If you dint get it, don't worry, I explained it assuming you'd already got the basics down.. go hit the subnetting section from the Networking / Protocols link at the top of the page, its explained very easily.

In the example above, wouldn't the number of host bits be 5 for mask 224?

Yes.

224 is 11100000. To figure out the number of networks (bits on the right), just take the number of bits on (111) and calculate that (be sure to add 1 for 0). So the number is 7 + 1 = 8, take out the 2 illegal numbers (000 and 111) and you have 6.

To get the hosts, just reverse this and make all the 0 bits = 1 and 1 bits = 0 or 00011111. Calculate that and you have 11111 = 31 + 1 = 32. Take out the illegal number (00000 and 11111) and you have 30 hosts.

This is just another way to look at it. There is another way to do it that I have used. If you look at the "Certifications, Books & More" forum and at the "Subnetting tips and tricks" at my tip, it says the same thing in a different way.

Everyone has there own way of remembering it, you just need to find out what works for you.

I don't know if you've looked at the subnetting topic on this site, but it is a good place to start.