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[music]

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So this is a review so far.

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We know that the original design

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of IP was that the address would

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be 32 bits long.

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We'll talk about the IANA

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in just a moment.

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Now, the way computers see

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it is it's it's just a single

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string of 32 bits.

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It's 32 bits end to end

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of an address.

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So really your computer says,

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Oh my IP address is 32,147,000,205.

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That's my IP address when

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I add up those 32 bits,

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if I was to convert that 32 bit

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number into a decimal number it'd

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be some monstrously

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large number in the billions.

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But we as human beings

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can't really work with that.

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If I ask you what the IP address

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is of your laptop hopefully you're

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not going to say,

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Oh it's 7,605,000,202.

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I'm going to walk away and

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I'm going to forget

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that 15 seconds later.

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So as human beings, we said okay,

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that 32 bit number,

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we have to come up with a way

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that we can use it,

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that's readable to us.

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So basically what we did

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is we said okay,

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let's take that string of 32 bits

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and cut it into four equal pieces.

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Four bytes, right?

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Each byte is 8 bits long.

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So 8, 8, 8, and 8.

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That gives us 32 bits.

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Then of each octet of each byte,

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we will convert that byte into a

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decimal number.

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Then we'll put dots

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in between them.

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So now we'll have 4 decimal numbers

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instead of just one monstrously

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long decimal number.

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So instead of seeing this--

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if I gave you that

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as my IP address,

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well that's fine for my computer.

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But as a human being,

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after I give you about the 9th bit,

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you're going to

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forget everything else.

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So we cut that into 4 equal pieces,

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convert it into decimal,

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and we get what's called

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dotted decimal,

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and that's actually

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the real dotted decimal

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equivalent of that 32-bit

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number that you see right there.

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The first 8-bits translate

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to the number 2.

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The next 8 bits translate

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to the number 234.

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The 3rd series of 8-bits

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translates to 107,

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and then the last octet,

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the last byte,

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is the number 18.

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And so, that's how,

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we as human beings,

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manipulate, and read,

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and type-in IP addresses,

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and this is what we call

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dotted decimal notation.

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Computing devices don't need this,

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they're perfectly fine with a

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string of thousands of bits,

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this is just for human convenience.

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Okay, so we talked about

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how on a broadcast domain,

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data could go out in 1 of 3

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different ways: broadcast,

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unicast, and multicast.

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And I said that when

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I'm transmitting data,

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when my NIC card for my laptop

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is transmitting data

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it needs to structure

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the Layer 2 and the Layer 3

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address to be appropriate

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to what it wants to do.

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So how does it do that?

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Well, we talked about Multicast.

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Multicast is actually

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real easy to represent.

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In the world of Layer 3 at IP

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if you take a look

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at the destination

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32-bit address so it's 32-bits

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going out as a destination address.

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If the 1st 4 of those bits match

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1110 that is a Multicast address.

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We don't care about what the

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remaining 28-bits look like.

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As long as the first 4 bits

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take that pattern that means this

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is a Multicast, one-to-many.

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Broadcast, now in the world of IP

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we known that an IP address

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it's sub dividable,

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part of it represents the network,

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the broadcast domain.

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The remaining part of it is

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what we call the host bits.

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Now in the case of a broadcast

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we've got two options now,

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and both of them look at this.

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One thing they both have in common

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is the host bits are all 1s.

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So in an IP address,

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if we take our focus away

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from the network portion,

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we forget about that,

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and we move to the

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second half of the address,

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the host portion of that address.

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If you ever see a 32-bit number

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that's an IP address in binary,

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and you see the host bits

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are all 1s just a continuous

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string of 1s,

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that means you're looking at

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a broadcast address.

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Now there are two different

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flavors of broadcast address.

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This first one right here

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that says any.111111.

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Let's say on the broadcast domain

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I'm on right now,

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my laptop is connected

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to a broadcast domain.

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Let's say it's been decided that

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the first 8-bits to identify my

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network is going to be in

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decimal the number 5.

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So I am on network number 5.

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You know 00000101.

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I'm on network number 5.

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If my laptop wants to send out a

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broadcast to just the devices in

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my own broadcast domain this is

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what's called a directed broadcast

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sometimes called a

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subnet broadcast.

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I want to talk to everybody

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in my domain only.

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Then the way I would structure my

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destination IP address is I would

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say in the network portion 5

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because that's my network.

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I'm on network number 5,

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and then the host portion is where

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I would put all of my 1s.

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If I'm in network 199,

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the network portion would

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say 199 in binary,

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and then the host portion

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would be all 1s,

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and that's a way of saying

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this is a directed broadcast.

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This is directed to everybody

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within my domain and

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my domain only.

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The second one downwards,

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the entire 32-bits end to end

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is just a continuous string of 1s.

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That's what's called a

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general broadcast that means to

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pretty much the entire world.

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Of course it's not going to go

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out to the entire world but that's

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what a general broadcast is.

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Where the entire

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32 bit number is all 1s.

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Vast majority of time I'd say

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probably I don't know,

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90% of the time when

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a laptop or a host,

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any host needs to create a

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broadcast it will choose

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the second option there.

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It'll create a broadcast where

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the destination IP address

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is just 32 bits of all 1s.

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If we convert that into

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dotted decimal that

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would be 255.255.255.255.

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So pretty much any protocol

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you can think of that

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utilizes broadcast

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like ARP, DHCP at Layer 3,

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the Layer 3 destination address

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will be all 1s the

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general broadcast address.

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Off the top of my head

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I can't think of any

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protocols that create

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directed broadcast which

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is the any .1111.

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There probably are some.

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I just can't think of any of it

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right now that actually do that.

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Then unicast.

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So we know that unicast is

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one-to-one communications

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from one device to another device.

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So it's pretty much any pattern

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that does not match the previous

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two patterns, except with all 0s.

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We know that any IP address that

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starts out with the first octet

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being all 0s, that is reserved.

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That's called the--

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that's actually used more

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for routing.

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That means it's going to everyone.

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It's not really going to everyone.

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It's what we call the

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default route basically.

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But it's not really reserved--

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it's a reserved address.

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So what's the takeaway from this?

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If you see a 32 bit pattern,

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in binary,

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and you are told that

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that is an IP address.

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Now somebody asks you,

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unlike a multiple choice question,

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identify is this IP address

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in binary unicast, multicast,

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broadcast, or none of the above.

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You should be able to do that

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because now you know what the

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pattern looks like in binary

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to identify those three.

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So up until this point in time,

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we have still retained this idea

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that an IP address was 32 bits

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long and only the first 8 bits

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represent the network.

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We had 24 bits of host space,

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8 bits of network space.

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Now, I mentioned at the very

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beginning that that really only

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left us with 254 networks,

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which back in 1969 was tons.

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Then as we started getting into

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even just a decade later into the

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late 1970s, it very quickly became

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apparent that this isn't going

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to work;

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254 networks is not enough.

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There is networks popping up

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all over the world

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which are modems,

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satellites and using Ethernet,

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we need more than 254 combinations.

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So the designers of IPs said,

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Okay, let's take this 32-bit number

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now and look at it a

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little bit differently.

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How can take-- how can we look at

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that 32-bit number and somehow

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come up with more than

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254 networks?

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Well, let's do this.

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Instead of just looking at the

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first 8-bits for the network,

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why don't we look at

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more than that.

288
00:09:29,500 --> 00:09:31,478
Why don't we take those host bits,

289
00:09:31,479 --> 00:09:34,196
sacrifice some of the host bits,

290
00:09:34,196 --> 00:09:35,359
and add them to the

291
00:09:35,360 --> 00:09:37,056
networking section,

292
00:09:37,056 --> 00:09:38,136
and they came up with

293
00:09:38,137 --> 00:09:40,075
classful addresses.

294
00:09:44,008 --> 00:09:45,954
So in 1981--

295
00:09:45,954 --> 00:09:47,264
and some of you watching might

296
00:09:47,265 --> 00:09:48,195
not have even been born

297
00:09:48,196 --> 00:09:49,757
back then, so in 1981,

298
00:09:49,758 --> 00:09:51,008
classes of addresses

299
00:09:51,009 --> 00:09:51,792
were introduced.

300
00:09:52,895 --> 00:09:54,379
So Class A,

301
00:09:54,380 --> 00:09:55,650
that was like the

302
00:09:55,651 --> 00:09:56,631
original way of doing it.

303
00:09:56,632 --> 00:09:58,431
A Class A address meant that the

304
00:09:58,432 --> 00:10:01,537
first 8-bits represent the network.

305
00:10:01,537 --> 00:10:03,247
The remaining 24 bits

306
00:10:03,248 --> 00:10:04,352
were for the host,

307
00:10:04,353 --> 00:10:06,273
so that was a Class A just like

308
00:10:06,274 --> 00:10:07,327
the beginning when it first was

309
00:10:07,328 --> 00:10:10,177
 invented in the late 1960s.

310
00:10:10,178 --> 00:10:11,065
But then they said, okay,

311
00:10:11,066 --> 00:10:15,040
we'll also have a Class B address.

312
00:10:15,041 --> 00:10:17,756
In a Class B address,

313
00:10:17,756 --> 00:10:18,997
instead of the first 8 bits

314
00:10:18,998 --> 00:10:20,218
representing the network,

315
00:10:20,219 --> 00:10:22,461
the first half of the address,

316
00:10:22,462 --> 00:10:24,771
the first 16 bits represent

317
00:10:24,772 --> 00:10:26,376
the network.

318
00:10:27,630 --> 00:10:29,784
In a Class C address,

319
00:10:29,785 --> 00:10:32,383
now 75% of the bits

320
00:10:32,384 --> 00:10:33,213
represent the network,

321
00:10:33,214 --> 00:10:35,329
the first 24 bits represent the

322
00:10:35,330 --> 00:10:39,292
network and only the last 8 bits

323
00:10:39,293 --> 00:10:41,971
represent hosts.

324
00:10:44,529 --> 00:10:45,717
Now the question is, okay,

325
00:10:45,718 --> 00:10:47,891
well if I put a 32-bit number in

326
00:10:47,892 --> 00:10:53,643
binary on a laptop or a PC,

327
00:10:53,644 --> 00:10:55,548
how does it know how to

328
00:10:55,549 --> 00:10:57,351
interpret that 32-bit number?

329
00:10:57,352 --> 00:10:58,622
Let me bring up a whiteboard

330
00:10:58,623 --> 00:11:01,992
here for a second so we can

331
00:11:01,993 --> 00:11:04,798
draw this. Okay.

332
00:11:04,799 --> 00:11:06,042
So here I've got some device.

333
00:11:06,043 --> 00:11:06,727
I'll just go ahead and

334
00:11:06,728 --> 00:11:10,955
draw a laptop or a PC, whatever.

335
00:11:10,956 --> 00:11:12,138
I'm going to give it some

336
00:11:12,139 --> 00:11:13,521
32-bit number.

337
00:11:14,609 --> 00:11:15,515
Actually I'll start off by giving

338
00:11:15,516 --> 00:11:16,875
it a 28-bit number.

339
00:11:16,876 --> 00:11:19,894
So 1 2 3 4 5 6 7 8 9 10 11 12 13

340
00:11:19,895 --> 00:11:22,885
14 15 16 17 18 19 20 21 2 3 4 5

341
00:11:22,886 --> 00:11:25,577
6 7 8. There's a 28 bit number.

342
00:11:26,877 --> 00:11:28,223
I'll leave off the first 4 bits

343
00:11:28,224 --> 00:11:28,906
on the front.

344
00:11:34,062 --> 00:11:35,197
Okay. So in the world of

345
00:11:35,198 --> 00:11:37,379
classful addressing,

346
00:11:38,196 --> 00:11:40,335
when you put an IP address

347
00:11:40,335 --> 00:11:41,370
on a device,

348
00:11:41,370 --> 00:11:43,062
32-bit number,

349
00:11:43,062 --> 00:11:44,354
the first thing that device did was

350
00:11:44,355 --> 00:11:48,124
look at the very first bit.

351
00:11:48,125 --> 00:11:52,363
If that first bit was a 0,

352
00:11:52,364 --> 00:11:54,242
then that device says okay,

353
00:11:54,242 --> 00:11:55,884
now I know exactly how many of

354
00:11:55,885 --> 00:11:57,279
these bits represent the network.

355
00:11:57,280 --> 00:11:59,801
If the first bit is a 0,

356
00:11:59,802 --> 00:12:03,717
that is a Class A address.

357
00:12:08,438 --> 00:12:10,456
and in a Class A address,

358
00:12:10,457 --> 00:12:12,159
just like the old days,

359
00:12:12,159 --> 00:12:15,280
the first 8 bits, the first byte,

360
00:12:15,281 --> 00:12:17,158
only is used to represent

361
00:12:17,159 --> 00:12:18,790
the network,

362
00:12:18,791 --> 00:12:20,441
and then all these other bits here

363
00:12:20,442 --> 00:12:21,923
is a unique host identifier for

364
00:12:21,924 --> 00:12:23,932
this one unique machine

365
00:12:23,933 --> 00:12:25,303
on this network.

366
00:12:27,220 --> 00:12:28,387
Now let's say he looks at

367
00:12:28,388 --> 00:12:29,520
this 32-bit address,

368
00:12:29,521 --> 00:12:31,934
and it starts out with a 1.

369
00:12:31,935 --> 00:12:32,456
Then he says,

370
00:12:32,456 --> 00:12:33,890
Okay, well this is not Class A.

371
00:12:33,891 --> 00:12:34,976
I need to look a little bit

372
00:12:34,977 --> 00:12:36,668
further to figure out

373
00:12:36,669 --> 00:12:38,502
what the class is.

374
00:12:38,503 --> 00:12:39,421
If he sees it after that

375
00:12:39,422 --> 00:12:42,057
the next is a 0,

376
00:12:42,058 --> 00:12:43,538
he says, I'm done.

377
00:12:43,538 --> 00:12:47,344
This is a Class B address,

378
00:12:47,345 --> 00:12:51,911
- which means for 5, 6, 7, 8 -

379
00:12:51,912 --> 00:12:53,196
which means that the first

380
00:12:53,197 --> 00:12:57,792
16 bits represent the network.

381
00:13:06,738 --> 00:13:08,103
So you can see here that with

382
00:13:08,104 --> 00:13:08,974
a Class A address,

383
00:13:08,975 --> 00:13:10,247
it's just like the old days.

384
00:13:10,248 --> 00:13:13,516
I've only got 254 unique numbers

385
00:13:13,517 --> 00:13:14,868
I can come up with.

386
00:13:14,868 --> 00:13:17,178
All 0s is reserved.

387
00:13:17,179 --> 00:13:19,354
All 1s is reserved.

388
00:13:19,355 --> 00:13:21,805
And then I have 254 combinations

389
00:13:21,806 --> 00:13:23,094
in the middle of that.

390
00:13:23,095 --> 00:13:25,181
So 254 networks.

391
00:13:25,182 --> 00:13:26,803
But if I tell my device,

392
00:13:26,804 --> 00:13:28,625
Oh, your address is a

393
00:13:28,626 --> 00:13:30,530
Class B address,

394
00:13:30,531 --> 00:13:31,175
well now I've got

395
00:13:31,176 --> 00:13:34,823
16 bits of network.

396
00:13:34,823 --> 00:13:37,145
That gives me tens of thousands--

397
00:13:37,146 --> 00:13:38,556
actually I think 16 bits gives

398
00:13:38,557 --> 00:13:41,646
you about 65,000 combinations

399
00:13:41,647 --> 00:13:42,710
of unique numbers

400
00:13:42,711 --> 00:13:43,614
you can come up with,

401
00:13:43,615 --> 00:13:45,423
a little bit more than that.

402
00:13:45,423 --> 00:13:46,203
So now we can see,

403
00:13:46,204 --> 00:13:47,152
Oh, I've got a lot more

404
00:13:47,153 --> 00:13:49,461
networks available with 16 bits,

405
00:13:49,462 --> 00:13:51,457
but what's the downside?

406
00:13:51,457 --> 00:13:53,288
You know with a Class A network,

407
00:13:53,289 --> 00:13:56,272
yeah, I've only got 254 of them,

408
00:13:56,273 --> 00:13:58,245
but on each one of those networks,

409
00:13:58,246 --> 00:14:01,183
I've got a lot of hosts.

410
00:14:01,184 --> 00:14:05,840
I've got 24 bits of host bits

411
00:14:05,841 --> 00:14:08,348
on a Class A network.

412
00:14:08,349 --> 00:14:11,571
That's 2 to the power of 24.

413
00:14:11,572 --> 00:14:12,484
I think that's something like

414
00:14:12,485 --> 00:14:14,954
16 million or something like that.

415
00:14:14,955 --> 00:14:18,037
So that means on one single cable,

416
00:14:18,037 --> 00:14:20,336
you could have about 16 million

417
00:14:20,337 --> 00:14:23,969
devices all in the same group,

418
00:14:23,970 --> 00:14:25,793
all at the same network address,

419
00:14:25,793 --> 00:14:28,243
not really feasible.

420
00:14:28,244 --> 00:14:29,934
With Class B,

421
00:14:29,934 --> 00:14:30,896
I've got a lot more

422
00:14:30,897 --> 00:14:32,599
networks available to me,

423
00:14:32,600 --> 00:14:33,933
but I'm sacrificing my host space.

424
00:14:33,934 --> 00:14:36,594
Now, instead of 24 bits for a host,

425
00:14:36,594 --> 00:14:39,302
I've only got 16 bits for host,

426
00:14:39,302 --> 00:14:41,707
which is still an awful lot.

427
00:14:41,708 --> 00:14:42,618
That means with Class B,

428
00:14:42,618 --> 00:14:44,604
I've got well over 65,000

429
00:14:44,605 --> 00:14:45,987
networks to me

430
00:14:45,988 --> 00:14:49,301
and each one of those networks

431
00:14:49,302 --> 00:14:51,884
also has 65,000 combinations of

432
00:14:51,885 --> 00:14:55,361
hosts it can have on that one wire,

433
00:14:55,362 --> 00:14:57,446
but they didn't stop there.

434
00:14:57,447 --> 00:15:00,194
They said, okay, if I give a device

435
00:15:00,195 --> 00:15:01,962
a 32-bit number as an IP address

436
00:15:01,963 --> 00:15:02,990
and it sees that the

437
00:15:02,991 --> 00:15:06,088
first two bits are 11,

438
00:15:06,089 --> 00:15:06,920
then it looks at the

439
00:15:06,921 --> 00:15:09,645
third bit as 110, now he says,

440
00:15:09,645 --> 00:15:11,286
Okay, now I know that of

441
00:15:11,287 --> 00:15:14,738
my 32-bit number, the first 24 bits

442
00:15:17,189 --> 00:15:17,875
- which would extend

443
00:15:17,876 --> 00:15:20,074
right about here -

444
00:15:20,075 --> 00:15:22,768
is my network address.

445
00:15:22,768 --> 00:15:24,744
That's our Class C address.

446
00:15:32,060 --> 00:15:33,396
So the Class C you can see

447
00:15:33,397 --> 00:15:34,680
there's even more networks.

448
00:15:34,681 --> 00:15:37,371
We've got 2 to the power of 24

449
00:15:37,372 --> 00:15:39,492
so we got millions and millions and

450
00:15:39,493 --> 00:15:41,898
millions of Class C

451
00:15:41,899 --> 00:15:43,574
networks available,

452
00:15:43,575 --> 00:15:45,136
but each one of those

453
00:15:45,137 --> 00:15:47,777
Class C networks only has 8 bits

454
00:15:47,778 --> 00:15:49,746
left over for host space,

455
00:15:52,295 --> 00:15:54,003
and we know the all 0s and

456
00:15:54,003 --> 00:15:56,629
all 1s hosts are reserved.

457
00:15:56,630 --> 00:15:59,122
So that means we got 254 hosts

458
00:15:59,123 --> 00:16:04,014
for each Class C network.

459
00:16:04,015 --> 00:16:05,032
So those are all the networks

460
00:16:05,033 --> 00:16:06,259
that were designed for

461
00:16:06,260 --> 00:16:08,203
unicast transmission

462
00:16:08,204 --> 00:16:09,635
for one-to-one transmission.

463
00:16:11,006 --> 00:16:13,099
See here, if I've got a Class A

464
00:16:13,100 --> 00:16:15,144
network that starts out with 0,

465
00:16:15,145 --> 00:16:15,746
so if I've got

466
00:16:15,747 --> 00:16:21,765
01234567.anything-- we know

467
00:16:26,653 --> 00:16:31,551
that this number is reserved.

468
00:16:31,551 --> 00:16:32,522
You can't start out any

469
00:16:32,523 --> 00:16:34,301
network with all 0s,

470
00:16:34,302 --> 00:16:35,221
and we also know that this

471
00:16:35,222 --> 00:16:38,482
number is reserved.

472
00:16:38,483 --> 00:16:39,266
You can't start out any

473
00:16:39,267 --> 00:16:41,328
network with that.

474
00:16:41,329 --> 00:16:43,047
So basically it tells us that from

475
00:16:43,048 --> 00:16:45,386
1.anything through-- actually,

476
00:16:48,173 --> 00:16:54,867
wait, hold on a second.

477
00:16:54,867 --> 00:16:56,343
It's still got to retain the 0

478
00:16:56,344 --> 00:16:58,442
in the first bit.

479
00:17:04,013 --> 00:17:05,551
So we've got in the middle here,

480
00:17:05,552 --> 00:17:07,556
1.anything,

481
00:17:07,557 --> 00:17:09,150
that's our first usable Class A

482
00:17:09,151 --> 00:17:12,792
network through and that number

483
00:17:12,793 --> 00:17:15,590
right there was 127.

484
00:17:19,348 --> 00:17:20,997
And that gets us back to our slide.

485
00:17:20,997 --> 00:17:23,081
That's where we saw this.

486
00:17:23,082 --> 00:17:24,998
Class A networks, technically,

487
00:17:24,999 --> 00:17:27,136
can't use the all 0s,

488
00:17:27,137 --> 00:17:28,748
so 1-dot-anything through

489
00:17:28,749 --> 00:17:30,817
127-dot-anything.

490
00:17:30,818 --> 00:17:33,887
Also it gets a little sticky here,

491
00:17:33,888 --> 00:17:34,532
but, technically,

492
00:17:34,533 --> 00:17:37,941
127 is also a reserved number.

493
00:17:37,942 --> 00:17:39,340
Just like a network number can't

494
00:17:39,341 --> 00:17:40,726
start out with all 0s and it can't

495
00:17:40,727 --> 00:17:42,311
start out with all 1s,

496
00:17:42,312 --> 00:17:44,442
127 is also a reserved number

497
00:17:44,443 --> 00:17:46,031
for special usage.

498
00:17:46,032 --> 00:17:47,988
It's called the loopback network.

499
00:17:47,989 --> 00:17:49,191
If you ever want to google that,

500
00:17:49,192 --> 00:17:50,622
the loopback network is anything

501
00:17:50,623 --> 00:17:52,437
that starts out with 127.

502
00:17:52,438 --> 00:17:54,030
So really,

503
00:17:54,031 --> 00:17:55,321
in your pursuit of your CCNA,

504
00:17:55,322 --> 00:17:57,406
what you need to memorize--

505
00:17:57,407 --> 00:17:57,982
you need to memorize

506
00:17:57,983 --> 00:17:59,337
a couple of things.

507
00:17:59,338 --> 00:18:01,032
You can identify a Class A network

508
00:18:01,033 --> 00:18:03,995
by the binary if the very first

509
00:18:03,996 --> 00:18:06,419
bit is a 0 that's Class A.

510
00:18:06,420 --> 00:18:07,496
And you should probably also

511
00:18:07,497 --> 00:18:10,494
memorize the dotted decimal.

512
00:18:12,179 --> 00:18:13,123
So I'm just going to put a line

513
00:18:13,124 --> 00:18:14,309
through this because

514
00:18:14,310 --> 00:18:15,277
127 is reserved

515
00:18:15,278 --> 00:18:22,323
for loop back so 126 dot anything.

516
00:18:22,324 --> 00:18:24,573
So the usable range of Class A

517
00:18:24,574 --> 00:18:27,758
networks are 1 dot anything up to

518
00:18:27,759 --> 00:18:31,238
126 dot anything,

519
00:18:31,239 --> 00:18:32,099
that's the usable range

520
00:18:32,100 --> 00:18:34,659
of Class A networks.

521
00:18:34,660 --> 00:18:35,879
Now when we go into Class B

522
00:18:35,880 --> 00:18:40,765
networks that starts out with 10,

523
00:18:40,766 --> 00:18:45,130
well 10000 is the number 128,

524
00:18:45,131 --> 00:18:49,085
and if I keep that pattern of 10--

525
00:18:49,086 --> 00:18:50,975
get rid of some of this here.

526
00:18:54,886 --> 00:18:59,184
10 and then 123456,

527
00:19:03,965 --> 00:19:08,265
and then 10123456,

528
00:19:09,920 --> 00:19:10,997
so that's my full range of

529
00:19:10,998 --> 00:19:12,762
Class B because we know Class B

530
00:19:12,763 --> 00:19:16,168
has to start with 10 in binary.

531
00:19:16,168 --> 00:19:17,547
So if I translate that back in a

532
00:19:17,548 --> 00:19:19,416
dotted decimal that's

533
00:19:19,417 --> 00:19:28,856
128 dot anything up to 191 dot

534
00:19:28,856 --> 00:19:32,520
anything so that's also something

535
00:19:32,521 --> 00:19:33,700
you should memorize as you pursue

536
00:19:33,701 --> 00:19:36,469
in your CCNA certification is that

537
00:19:36,470 --> 00:19:37,433
Class B is recognizable

538
00:19:37,434 --> 00:19:39,343
in binary by any IP address that

539
00:19:39,344 --> 00:19:41,631
starts out with 10 and is

540
00:19:41,632 --> 00:19:43,888
recognizable in dotted decimal

541
00:19:43,889 --> 00:19:45,697
by any IP address that falls within

542
00:19:45,698 --> 00:19:49,642
the range of 128 up to 191.

543
00:19:52,129 --> 00:19:53,136
Then finally we have our

544
00:19:53,137 --> 00:19:54,957
Class C addresses.

545
00:19:58,109 --> 00:19:59,721
We know that Class C in binary

546
00:19:59,722 --> 00:20:03,336
starts with 110 so the

547
00:20:03,337 --> 00:20:04,107
smallest number

548
00:20:04,108 --> 00:20:05,771
we could come up with that retains

549
00:20:05,772 --> 00:20:08,709
that pattern is that,

550
00:20:10,544 --> 00:20:11,656
and the largest number that

551
00:20:11,657 --> 00:20:12,974
we could come up that retains

552
00:20:12,975 --> 00:20:16,006
that pattern is that.

553
00:20:20,717 --> 00:20:24,228
So here we have 192 dot anything.

554
00:20:26,444 --> 00:20:28,336
That's the smallest Class C network

555
00:20:28,337 --> 00:20:30,284
anything that begins with 192

556
00:20:32,553 --> 00:20:37,151
and 223 dot anything.

557
00:20:37,152 --> 00:20:38,421
So this is your full range

558
00:20:38,422 --> 00:20:40,221
of Class C networks.

559
00:20:40,222 --> 00:20:42,183
Anything that starts out with 110

560
00:20:42,184 --> 00:20:44,217
in binary or in dotted decimal,

561
00:20:44,218 --> 00:20:45,434
anything that falls within the

562
00:20:45,435 --> 00:20:48,498
range of 192 to 223.

563
00:20:51,539 --> 00:20:52,445
That's what we see here.

564
00:20:53,688 --> 00:20:55,762
Class D networks,

565
00:20:55,763 --> 00:20:58,058
this is reserved for multicast.

566
00:20:58,059 --> 00:20:59,307
So if I've got that situation

567
00:20:59,308 --> 00:21:01,371
where I'm sending one sender,

568
00:21:01,372 --> 00:21:02,951
one transmitter is sending a

569
00:21:02,952 --> 00:21:05,409
single stream of data that multiple

570
00:21:05,410 --> 00:21:07,551
devices are going to pick up,

571
00:21:07,552 --> 00:21:08,872
but I don't want to be for everyone

572
00:21:08,873 --> 00:21:09,728
- it's not a broadcast,

573
00:21:09,729 --> 00:21:11,422
it's a multicast -

574
00:21:11,423 --> 00:21:12,140
then you would use an

575
00:21:12,141 --> 00:21:14,247
address in the Class D space,

576
00:21:16,311 --> 00:21:17,669
and the way you would recognize

577
00:21:17,670 --> 00:21:25,787
that in binary and you start to

578
00:21:25,788 --> 00:21:26,980
see the pattern right here

579
00:21:27,701 --> 00:21:29,129
are the first 4 bits.

580
00:21:36,942 --> 00:21:41,321
So the smallest multicast address

581
00:21:41,322 --> 00:21:43,689
is anything beginning with 224,

582
00:21:48,250 --> 00:21:49,624
and that's the largest multicast

583
00:21:49,624 --> 00:21:58,215
address which is 239 dot anything

584
00:21:59,637 --> 00:22:01,686
so that's your range of multicast

585
00:22:01,687 --> 00:22:04,493
addresses all starting with 1110

586
00:22:04,494 --> 00:22:06,663
in binary and dotted decimal

587
00:22:06,664 --> 00:22:10,586
falling in the range of 224 to 239.

588
00:22:11,828 --> 00:22:13,246
And then the last range

589
00:22:13,247 --> 00:22:14,977
of networks is--

590
00:22:14,978 --> 00:22:16,104
I wouldn't even say networks.

591
00:22:16,105 --> 00:22:19,734
The last range of classful IP

592
00:22:19,735 --> 00:22:20,996
addresses is what's called the

593
00:22:20,997 --> 00:22:22,089
Class E.

594
00:22:22,090 --> 00:22:23,101
This was originally known

595
00:22:23,102 --> 00:22:25,186
as the experimental range.

596
00:22:25,826 --> 00:22:27,195
And if we go to our binary

597
00:22:27,196 --> 00:22:27,681
once again,

598
00:22:27,682 --> 00:22:28,761
you can see it's going to be the

599
00:22:28,762 --> 00:22:30,912
next pattern available to us.

600
00:22:33,382 --> 00:22:35,407
So Class E experimental addresses

601
00:22:35,408 --> 00:22:40,312
start out with 1110,

602
00:22:40,313 --> 00:22:44,227
so the first 5 bits are 11110.

603
00:22:45,087 --> 00:22:46,113
You're never going to see any

604
00:22:46,114 --> 00:22:49,614
IP packet with a Class E

605
00:22:49,615 --> 00:22:52,220
source or destination.

606
00:22:52,221 --> 00:22:55,973
It was reserved as future use and

607
00:22:55,974 --> 00:22:57,701
it never really came to fruition.

608
00:22:57,701 --> 00:22:59,178
So even today and here we are

609
00:22:59,179 --> 00:23:01,995
in 2015 where IPv4 networks

610
00:23:01,996 --> 00:23:03,316
are almost entirely gone,

611
00:23:03,317 --> 00:23:04,845
almost entirely used up,

612
00:23:05,744 --> 00:23:07,915
this space has never been utilized

613
00:23:07,916 --> 00:23:09,656
and will never be utilized,

614
00:23:09,657 --> 00:23:11,282
Class E.

615
00:23:12,011 --> 00:23:14,107
If you're curious as to why,

616
00:23:14,107 --> 00:23:15,840
if you're watching this in

617
00:23:15,841 --> 00:23:17,564
the live class right now,

618
00:23:17,565 --> 00:23:20,254
in the files section in the

619
00:23:20,255 --> 00:23:22,270
upper right you'll see I've

620
00:23:22,271 --> 00:23:24,118
 included a PDF of the slides,

621
00:23:24,119 --> 00:23:25,218
and in the notes section

622
00:23:26,087 --> 00:23:28,428
I've included a URL in there that

623
00:23:28,429 --> 00:23:30,987
talks about why Class E

624
00:23:30,988 --> 00:23:32,263
is never going to be used.

625
00:23:32,264 --> 00:23:33,811
Just to really briefly summarize

626
00:23:34,919 --> 00:23:37,068
for the last, I don't know,

627
00:23:37,069 --> 00:23:40,130
3 or 4 decades the

628
00:23:40,131 --> 00:23:42,134
IP protocol stack,

629
00:23:42,135 --> 00:23:44,427
the code that implements IP

630
00:23:44,428 --> 00:23:46,627
has been written in such a way

631
00:23:46,628 --> 00:23:47,699
that whether that code is

632
00:23:47,700 --> 00:23:49,422
implemented on a router,

633
00:23:49,423 --> 00:23:51,573
or a laptop, or a tablet,

634
00:23:51,573 --> 00:23:53,201
or a smartphone,

635
00:23:53,201 --> 00:23:55,255
every device has always recognized

636
00:23:55,256 --> 00:23:58,117
that Class E is not usable.

637
00:23:58,118 --> 00:24:00,021
If you try putting a Class E

638
00:24:00,022 --> 00:24:01,645
address on your laptop,

639
00:24:01,646 --> 00:24:04,185
or on a smartphone, or on a router,

640
00:24:04,186 --> 00:24:05,893
you'll get an error message because

641
00:24:05,894 --> 00:24:07,381
it recognizes in the code that

642
00:24:07,382 --> 00:24:10,023
this is reserved for future use.

643
00:24:10,024 --> 00:24:11,121
So some people have said,

644
00:24:11,122 --> 00:24:12,498
well, here we are today

645
00:24:12,499 --> 00:24:13,671
in the modern world,

646
00:24:14,415 --> 00:24:14,047
we need this space.

647
00:24:14,048 --> 00:24:17,343
we've run out of IPv4 addresses.

648
00:24:17,344 --> 00:24:19,610
Let's reclaim the Class E so we

649
00:24:19,611 --> 00:24:22,458
can get some more space out of it.

650
00:24:22,459 --> 00:24:24,237
Well that URL in the PDF

651
00:24:24,238 --> 00:24:25,152
goes into a little bit of detail.

652
00:24:25,153 --> 00:24:26,891
Basically it says well let's

653
00:24:26,892 --> 00:24:28,951
think about that for a second.

654
00:24:28,951 --> 00:24:30,099
With the way that people

655
00:24:30,100 --> 00:24:31,323
are using IP these days,

656
00:24:31,324 --> 00:24:33,164
with how many new networks are

657
00:24:33,165 --> 00:24:36,231
coming online every single day,

658
00:24:36,232 --> 00:24:38,596
if theoretically we could use

659
00:24:38,597 --> 00:24:40,692
the Class E space,

660
00:24:40,692 --> 00:24:44,322
that might extend the usable life

661
00:24:44,323 --> 00:24:48,627
of IPv4 for maybe another 5 or

662
00:24:48,628 --> 00:24:50,922
6 years, maybe,

663
00:24:50,923 --> 00:24:52,914
but what would that require?

664
00:24:52,915 --> 00:24:54,491
That would require that all the

665
00:24:54,492 --> 00:24:56,682
software developers that developed

666
00:24:56,683 --> 00:25:00,178
Windows, Linux, and the Apple

667
00:25:00,179 --> 00:25:01,679
operating systems-- they have to go

668
00:25:01,680 --> 00:25:03,520
back into their code,

669
00:25:03,521 --> 00:25:05,491
rewrite the code so that this is

670
00:25:05,491 --> 00:25:06,901
now an acceptable address.

671
00:25:06,902 --> 00:25:08,452
It wouldn't spit out an error.

672
00:25:08,453 --> 00:25:09,137
It would recognize that

673
00:25:09,138 --> 00:25:10,420
as being useful,

674
00:25:10,421 --> 00:25:11,702
and what about you that

675
00:25:11,703 --> 00:25:13,399
already own a laptop,

676
00:25:13,400 --> 00:25:14,351
how are you going to go into your

677
00:25:14,352 --> 00:25:18,730
IPv4 code and change it so that

678
00:25:18,731 --> 00:25:20,580
it now recognizes that this is okay

679
00:25:20,581 --> 00:25:22,149
it's all right to see that,

680
00:25:22,150 --> 00:25:23,325
you can't.

681
00:25:23,326 --> 00:25:24,201
So they said,

682
00:25:24,202 --> 00:25:25,416
look the time and the effort

683
00:25:25,417 --> 00:25:29,427
it would take to take all the new

684
00:25:29,428 --> 00:25:30,993
equipment that's being developed to

685
00:25:30,994 --> 00:25:32,945
recognize that as being all right,

686
00:25:32,945 --> 00:25:35,125
and to somehow go to everybody's

687
00:25:35,126 --> 00:25:37,916
existing smartphone, and tablet,

688
00:25:37,917 --> 00:25:39,319
and PC and say okay,

689
00:25:39,320 --> 00:25:41,356
it's okay now, it's all right,

690
00:25:41,357 --> 00:25:44,326
it's not theoretically possible to

691
00:25:44,327 --> 00:25:44,905
do that.

692
00:25:44,906 --> 00:25:46,800
It's just not feasible to do that

693
00:25:46,801 --> 00:25:48,106
as a end result to only

694
00:25:48,107 --> 00:25:49,424
give yourself maybe

695
00:25:49,425 --> 00:25:52,246
5 extra years of life of IPv4.

696
00:25:52,247 --> 00:25:53,471
So that's why Class E

697
00:25:53,472 --> 00:25:55,442
will never come to anything,

698
00:25:55,443 --> 00:25:57,268
just won't be usable for anything.

699
00:25:59,096 --> 00:26:00,197
And somebody has asked--

700
00:26:00,198 --> 00:26:02,113
so Ganesh has asked me to

701
00:26:02,114 --> 00:26:03,686
elaborate a little bit on what this

702
00:26:03,687 --> 00:26:08,274
concept is of the loopback address,

703
00:26:08,275 --> 00:26:09,283
which is basically anything

704
00:26:09,284 --> 00:26:11,043
beginning with 127.

705
00:26:12,680 --> 00:26:13,508
Basically the way

706
00:26:13,509 --> 00:26:19,554
I understand this is that any

707
00:26:19,555 --> 00:26:22,683
device that's running IP whether it

708
00:26:22,684 --> 00:26:24,074
be a router or a laptop

709
00:26:24,075 --> 00:26:24,986
or a tablet,

710
00:26:25,997 --> 00:26:27,266
when you tell that device,

711
00:26:27,267 --> 00:26:29,098
Hey, I want you to create a packet,

712
00:26:30,258 --> 00:26:31,804
and I want the destination of

713
00:26:31,804 --> 00:26:36,800
that packet to be 127 dot anything,

714
00:26:36,801 --> 00:26:39,198
the way the device interprets it,

715
00:26:39,198 --> 00:26:40,595
it says, Okay, well that means that

716
00:26:40,596 --> 00:26:43,935
basically I'm testing myself.

717
00:26:43,935 --> 00:26:46,204
I'm testing to see if my own

718
00:26:46,205 --> 00:26:47,352
IP protocol

719
00:26:47,353 --> 00:26:50,226
is working and is functional.

720
00:26:50,227 --> 00:26:51,388
So when you tell a device like

721
00:26:51,389 --> 00:26:53,421
a laptop or PC or router to create

722
00:26:53,422 --> 00:26:56,077
a packet going to 127 dot anything,

723
00:26:56,078 --> 00:26:58,003
it will create that packet,

724
00:26:58,004 --> 00:26:59,088
but it never leaves the brain

725
00:26:59,089 --> 00:27:00,198
of the device.

726
00:27:00,199 --> 00:27:01,647
It will never actually go on the

727
00:27:01,648 --> 00:27:03,518
wire and go anywhere.

728
00:27:03,518 --> 00:27:04,163
It's like you're

729
00:27:04,164 --> 00:27:05,560
talking to yourself.

730
00:27:05,561 --> 00:27:07,083
It's like, Hey, IP are you there?

731
00:27:07,084 --> 00:27:07,920
Yep, I'm here.

732
00:27:07,921 --> 00:27:08,977
Okay, we're good.

733
00:27:08,978 --> 00:27:10,602
So that's what they mean

734
00:27:10,603 --> 00:27:11,307
by loopback.

735
00:27:11,308 --> 00:27:12,642
It doesn't leave the device

736
00:27:13,327 --> 00:27:14,185
it's basically a way of just

737
00:27:14,186 --> 00:27:16,034
testing to see if your own

738
00:27:16,035 --> 00:27:18,135
IP protocol is working.

739
00:27:19,339 --> 00:27:19,945
So for example,

740
00:27:19,946 --> 00:27:22,194
if I open up a DOS prompt here,

741
00:27:24,018 --> 00:27:25,415
if I ever was wondering,

742
00:27:25,416 --> 00:27:26,551
I say, Oh, you know,

743
00:27:26,552 --> 00:27:27,874
I can't get to the Internet,

744
00:27:27,875 --> 00:27:29,178
I can't get to my email server,

745
00:27:29,179 --> 00:27:30,101
I can't get to anything.

746
00:27:30,500 --> 00:27:33,088
I wonder if there is some bug in my

747
00:27:33,089 --> 00:27:36,152
Microsoft implementation of IPv4

748
00:27:36,153 --> 00:27:37,162
in my laptop.

749
00:27:37,163 --> 00:27:39,731
Could IPv4 be buggy in my laptop?

750
00:27:39,732 --> 00:27:40,834
I can test that by just saying,

751
00:27:40,835 --> 00:27:43,924
ping 127.pretty much anything,

752
00:27:43,925 --> 00:27:45,306
5.6.7.

753
00:27:46,140 --> 00:27:47,101
And the fact that I'm getting

754
00:27:47,102 --> 00:27:50,350
a reply tells me that my own local

755
00:27:50,351 --> 00:27:52,579
implementation of IPv4 is okay.

756
00:27:52,580 --> 00:27:54,340
I've just basically pinged

757
00:27:54,340 --> 00:27:56,456
my own CPU.

758
00:27:56,457 --> 00:27:58,585
So that's what the loopback network

759
00:27:58,585 --> 00:27:59,949
is used for.

760
00:27:59,950 --> 00:28:00,842
And really doesn't matter

761
00:28:00,843 --> 00:28:04,842
what it is, 127.88.99.100,

762
00:28:04,843 --> 00:28:05,917
just the fact that it's beginning

763
00:28:05,918 --> 00:28:09,084
with 127 tells the IP protocol

764
00:28:09,085 --> 00:28:10,294
implementation that this is a

765
00:28:10,295 --> 00:28:12,853
loopback test.

766
00:28:12,853 --> 00:28:14,530
You can do this on a router,

767
00:28:14,531 --> 00:28:15,254
or a laptop,

768
00:28:15,255 --> 00:28:16,828
or anything that gives you the

769
00:28:16,829 --> 00:28:20,453
ability to send a packet to 127,

770
00:28:21,479 --> 00:28:24,182
so that's what that's reserved for.

771
00:28:24,182 --> 00:28:25,928
Well if you don't have

772
00:28:25,929 --> 00:28:28,327
any questions for me,

773
00:28:28,328 --> 00:28:30,486
I've got some questions for you.

774
00:28:30,487 --> 00:28:31,311
So I promised you that

775
00:28:31,311 --> 00:28:32,139
during this presentation,

776
00:28:32,140 --> 00:28:33,405
I'll have some periodic quiz

777
00:28:33,406 --> 00:28:34,529
questions that would pop up.

778
00:28:35,650 --> 00:28:36,610
So I'm going to give you a couple

779
00:28:36,611 --> 00:28:38,532
of them right now and then we'll

780
00:28:38,533 --> 00:28:39,498
take our first break.

781
00:28:39,997 --> 00:28:40,842
Here's what I'm going to do.

782
00:28:40,843 --> 00:28:44,630
These questions should be

783
00:28:44,631 --> 00:28:45,858
pretty quick for you to answer.

784
00:28:45,859 --> 00:28:47,413
So I will display the question.

785
00:28:47,414 --> 00:28:48,489
I'll maximize it here

786
00:28:48,490 --> 00:28:49,334
so you don't see me.

787
00:28:50,631 --> 00:28:51,750
And when you see the question,

788
00:28:51,751 --> 00:28:53,978
I will give you 30 seconds to think

789
00:28:53,979 --> 00:28:55,589
about it, come up with the answer.

790
00:28:55,590 --> 00:28:56,532
You don't have to type in the

791
00:28:56,533 --> 00:28:57,471
answer if you don't want to,

792
00:28:57,472 --> 00:28:58,710
just try to come up with it

793
00:28:58,711 --> 00:28:59,358
on your own.

794
00:29:00,071 --> 00:29:01,064
And after 30 seconds,

795
00:29:01,065 --> 00:29:03,214
I will show you the answer

796
00:29:03,214 --> 00:29:04,816
and we'll talk about it.

797
00:29:04,817 --> 00:29:07,877
So let's go to question number 1.

798
00:29:07,877 --> 00:29:10,164
Identify which of the IP addresses

799
00:29:10,165 --> 00:29:13,709
below belong to a Class B network.

800
00:29:13,710 --> 00:29:15,024
You have 30 seconds.

801
00:29:15,025 --> 00:29:15,848
And if you're watching this

802
00:29:15,848 --> 00:29:16,896
as a recorded session,

803
00:29:16,897 --> 00:29:18,174
you can just press the pause button

804
00:29:18,175 --> 00:29:20,028
right now to pause this recording,

805
00:29:20,627 --> 00:29:21,699
and then play it when you think

806
00:29:21,700 --> 00:29:22,367
you have the answer.

807
00:29:23,923 --> 00:29:25,521
Okay, so it's been 30 seconds.

808
00:29:25,522 --> 00:29:26,473
So which of these are

809
00:29:26,474 --> 00:29:27,557
Class B networks?

810
00:29:29,040 --> 00:29:30,967
Here is your answer.

811
00:29:30,968 --> 00:29:34,300
Answer C and D.

812
00:29:34,301 --> 00:29:35,360
We know that binary,

813
00:29:35,361 --> 00:29:36,552
any IP address that begins

814
00:29:36,553 --> 00:29:37,656
with a combination

815
00:29:37,657 --> 00:29:39,830
of 10 is a Class B network.

816
00:29:39,831 --> 00:29:41,955
That's why answer C is correct.

817
00:29:42,792 --> 00:29:43,578
And we know that if it

818
00:29:43,579 --> 00:29:44,681
begins with 10,

819
00:29:44,682 --> 00:29:46,229
that means the range of Class B

820
00:29:46,230 --> 00:29:49,438
networks is anything from 128 up

821
00:29:49,439 --> 00:29:51,828
to 191.

822
00:29:51,829 --> 00:29:54,823
And that's why answer D is

823
00:29:54,824 --> 00:29:56,617
also the correct answer.

824
00:29:56,618 --> 00:29:58,558
Let's go on to the next one.

825
00:29:59,161 --> 00:30:00,476
Identify which of the IP addresses

826
00:30:00,477 --> 00:30:04,190
below belong to a Class C network?

827
00:30:05,719 --> 00:30:08,521
Okay, time is up.

828
00:30:08,522 --> 00:30:10,052
So Class C network,

829
00:30:10,053 --> 00:30:11,356
the answers would be

830
00:30:11,357 --> 00:30:13,390
answers B and E.

831
00:30:13,391 --> 00:30:14,178
With Class C,

832
00:30:14,179 --> 00:30:15,559
anything in binary that

833
00:30:15,560 --> 00:30:18,650
begins with 110 is Class C.

834
00:30:18,651 --> 00:30:20,488
And in dotted decimals,

835
00:30:20,489 --> 00:30:21,796
that means your first octet

836
00:30:21,797 --> 00:30:22,446
is going to fall

837
00:30:22,446 --> 00:30:23,332
within the range of

838
00:30:23,333 --> 00:30:27,894
192 up to 223.

839
00:30:27,895 --> 20:28:44,146
[music]