Original subtitles

So here's some practice for subletting.

We're going to start practicing right away with a sample question.

And this question is.

A host has the IP address one nine eight eight two two four five six eight one seven three two six.

So what do you suppose are the network addresses, the broadcast addresses and the valid host addresses

for the IP subnet, of which the host is a member of.

Oh, and there's a second part to this question.

What is this subnet mask and the dotted decimal notation?

OK, don't worry, I'm not leaving you on your own.

We're going to have a look at how we're going to figure out the answer.

So we're going to do the second part for us because it's easier and it's actually more logical the answer

to that question that way.

So the second part of the question was what's going to be the sub mask slash 26 in dotted decimal?

So the way that you actually do this, when you first learning's of netting is to write out the bit

pattern at the top of a piece of paper.

Then later on, you will be able to do it in your head, but when you're first learning, it's a whole

lot easier to just write it all out.

OK, so take a piece of paper.

Start at the top and from right to left right out.

One two four eight 16, 32 64 128.

Make sure you put a dot between each number.

OK, so it's going to look like this.

Court now proceed to the next octet until you've written down the bit pattern for the four octet in

a subnet mask like this.

Good, so the subnet mask and our example question is Slash 26.

So under your bed pattern at the top of the paper, right out 26 ones underneath.

Starting from the left side.

Then you can fill in the remainder with zeros for the host portion of the address.

You got it.

Now, draw a line in after the 26 ones to indicate the demarcation point between the network and the

host portions of the address.

Remember, the network portion is to the left of the line and the host portion is to the right of it.

Good, so we can just add up the ones to find the subnet mask in dotted decimal notation.

So the first octet is all ones 128 plus 64 plus 32 plus 16 plus eight plus four plus two plus one equals

255.

So 255 is the answer.

2ND and third octet are also old ones, adding up to 255, so now we've got two five five two five five

two five five.

And for the fourth octet, the ones are under 128 and 64, so 128 plus 64 equals 192.

Therefore, the subnet mask was slashed 26 in dotted decimal notation is two five five two five five

two five five not one nine two.

Now, what was the other part of the question again?

Yeah.

What is the network addressed the broadcast address and a valid host address for the IP address.

One nine two two eight two two eight four five one seven three eight two six.

Well, I'll tell you some again, piece of paper is going to come in handy.

So we're going to write out the IP address and dotted decimal notation now as well.

So the IP address in our example question is one nine eight Dot two to Dot four or five dot one seven

three.

So when we start with the first octet one nine eight.

Starting from the one to eight bit on the left, right down to one under the bit, if it adds up to

less than the number in the IP address, he yeah, let me just explain it quick.

The first octet is one nine eight, so one two eight is less than one 980, so we write down or one

under the one two eight.

OK, so the next bit after one to eight is 64, 128 plus 64 is 192.

OK, so one nine two is less than one 980, so we write a one under the 64.

The next bit after 64 is 32.

One two, eight six four plus three two equals two to four.

Now 224 is more than 198, so that means we'll write a zero, not a one under the 32.

And the next bit after 32 is 16.

All right, so far we have 128 plus 64 equals, 192 192 plus 16 equals 208.

And of course, 208 is more than 198.

So we write in zero under the 16.

The next bit after the 16 is eight one, 92 plus eight equals 200 and 200 is more than 198.

So we write a zero under the eight.

Next bit after the eight is four one nine two plus four is one nine six one nine six is less than one

nine eight, so we write a one under the for next bit after four is two, so one nine six plus two equals

198 198 is exactly 198.

So we write our one under the two.

So we got to the exact number, right?

That means that we've finished calculating this octet so we can write a zero for all the remaining bits.

You get it.

Which is actually here in this example, just the final one bit at the end.

So now that we got a written down, we can quickly add up the ones to check, our answer adds up to

the one nine eight first octet in our one nine eight two two four five eight one seven three IP address.

OK, we'll do it together.

128 plus 64 plus four plus two equals one hundred ninety eight.

Then we just repeat the process for the other three tests in order to write out the entire IP address.

One nine eight two two four or five one seven three and dotted decimal notation.

Now we're working with a slash 24 subnet mask, so the network portion of this address is a first 26

bit.

The first 24 bits, the first three octet are one nine eight, not two, two, not four or five.

We can easily see that right just by looking at the IP address.

Then we just count whatever it is in the fourth octet, first to bid to get all 26 bits.

So I've got a one for one 28 and a zero for 64.

So that's going to add up to 128.

All right.

So the network address is one nine eight two two eight four five eight one two eight.

Cool.

So that's the first part of the question.

That's right.

Did you forget about the second part?

Well, next up is to figure out the broadcast addresses.

So the broadcast address is the final IP address in this IP subnet, which is one less than the network

address of the next IP subnet.

So the network address of this IP subnet is one nine eight two, two four or five Dot one 28.

Right, because we just calculated.

Now, looking at the line, which demarcates the network and host partitions of the address, we can

see that after it is 64.

So that means the IP subnets are going up in increments of 64.

And as you can also see from the Red Line, we are subletting on the 4th Octet.

So this IP subnet is one nine, eight, two, two, four or five.

Got one to eight.

Now, to calculate the next I.P. step that we had 64 to the octet we are submitting on, which is the

fourth octet in this case, one two eight plus 64 equals 192.

You still with me.

So see, the network address of the next IP subnet is one less than one nine two two two two four five

eight one nine two.

And that would be one nine eight nine eight two two four five eight one nine one.

So that makes a broadcast address of this one, nine, eight, two, 2.4 or 5.1 to eight subnet.

One nine eight two two four five eight one nine one.

Cool, so now we've got the network address and the broadcast address.

So finally, we just need to determine the possible host addresses.

Now they happen to be all the addresses between the network address of one nine eight two two 2.4 or

5.1 one two eight.

And the broadcast address of one nine eight two two four or five eight one nine one.

So that gives us one, nine, eight, two, two, four or five, not one to nine all the way through

one nine eight talked to two, not four or five, not one nine zero.

Now a final and important point to tell you here is notice that all our calculations were done on the

octet where the subnet line is.

So this example is a slash 26 that is in the fourth octet.

So we don't actually need to worry about the first three octet.

Now you get it because they're always going to be unchanged.

One nine, eight, two, two, four or five, in our example.

So when you're working on a sub that in question, you only need to write out the octet that this sub

netting is actually happening on because all the other architects are always going to just be there

unchanged, you don't have to write out the whole IP address in full every time.

I know that's a load off.

So that's it, right?

That's how you practice up netting.

So take it away.

It's all yours, you can practice that all you want.

But.

We're going to move on to IPv6 in the next lesson.

I'll see you then.