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In this lesson,

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we're going to discuss IPv4 addressing.

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Now, IPv4, or Internet Protocol version 4,

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is extremely popular, and it's the most common type

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of IP addressing used in our networks.

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In fact, if you're like most people,

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you've probably seen an IPv4 address before.

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When you look at them, they're written as a series

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of four decimal numbers separated by dots.

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Some examples of an IPv4 address

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are things like 10.1.2.3

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or 172.21.243.67

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As you can see, each IPv4 address

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is made up of four different parts to form that address,

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and this is why we call it a dotted-decimal notation.

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When you're referring to each

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of those four parts individually though,

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we call these an octet

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because each of them is a decimal number that's being used

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to represent eight bits of a binary number.

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Now, since each octet uses a decimal number

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to represent an eight-bit binary number,

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each octet can be represented by value of 0 to 255

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in each of those four octets of an IPv4 address.

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Now, when all four octets are combined,

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we get four octets that contain eight bits each

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for a total of 32 bits of total addressable space

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when using an IPv4 address.

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Now, for example, let's say you have the IPv4 address

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of 192.168.1.4

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That is being written in dotted-decimal notation

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to make it easier for you and I as humans to read it,

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but to a computer, that actually isn't what it is.

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Instead, they understand this as binary,

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which is 11000000

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.10101000

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.00000001

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.00000100

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Now, as you can see, using the dotted-decimal notation

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is a lot easier for us to read out loud and for us to type,

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and so it's less prone for us experiencing human error

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when we enter those numbers

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into our network device configurations,

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and it's a lot easier to memorize

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the decimal version of this than the binary.

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Now, each IPv4 address is actually going to be created

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using two portions, which we refer to as the network portion

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and the host portion of the address.

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So when you get an IP address like 192.168.1.4,

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it's actually broken down into these two portions,

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the network and the host portion,

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by using a second 32-bit number known as a subnet mask.

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Now, when you look at a subnet mask in decimal form,

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it's going to look a lot like an IPv4 address,

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but if you look at it in binary form,

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you're going to see there's actually continuous strings

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of ones and zeros,

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with the ones identifying the network portion

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and the zeros identifying the host portion

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of that IPv4 address that it's going to be married up with.

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For example, let's say I have a subnet mask

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of 255.255.255.0

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Now, if we converted each of these octets into binary,

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we would actually get 11111111.

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11111111.

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11111111.

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00000000

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Notice we have three sets of eight ones

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and then one set of eight zeros in our binary form

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to represent the decimal equivalent of 255.255.255.0

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Now, when you look at that subnet mask, and you see a one

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in that binary representation of the subnet mask,

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this becomes the network portion of the IPv4 address.

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If you see a zero in the binary representation

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of the subnet mask, this becomes the host portion

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of the IPv4 address.

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So let's put this together by showing both the IPv4 address

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and its associated subnet mask.

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First, we have our IPv4 address of 192.168.1.4

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Next, we have our subnet mask underneath it

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of 255.255.255.0

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Now, anytime I see a 255 in my decimal representation,

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this is representing all ones if we converted it to binary,

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so it becomes part of that network portion

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of the IPv4 address.

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So in this case, the 192.168.1

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is our network portion of the address.

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Anytime I see an IPv4 address

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that starts with 192.168.1.something,

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this means that it's addressable

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as part of this local network because all those things

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are going to be part of this network portion.

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Now, everywhere I see those zeros in the subnet mask,

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this actually represents the host portion

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of the IPv4 address.

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In this case, that's the .4 portion of the address

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of 192.168.1.4 that we had before.

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And that .4 is going to represent this specific host,

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like a server, a desktop, a laptop,

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a tablet, a printer, or any other network device

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that was assigned this IPv4 address.

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So if I have an address like 192.168.1.50

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with a subnet 255.255.255.0,

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that device is on the same network

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as our 192.168.1.4 device,

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and they can communicate to each other using a switch,

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and we wouldn't even have to use a router

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because they're on the same network.

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This means our switch will transfer data back and forth

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between these two devices using just their MAC addresses,

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and we're not going to have to route traffic

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using a router between these two devices.

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Now, on the other hand, if I had a device like 172.16.0.100

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with a subnet mask of 255.255.255.0,

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this tells me that that device is on a different network,

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and specifically, it's on the 172.16.0.something network.

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So we're not going to be able to communicate

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with the original device at 192.168.1.4

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without leaving its network, routing the traffic

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to this new network of 172.16.0.something,

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and that way you have to do that using a router

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or a layer 3 switch to make that routing happen.

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Now, if this doesn't quite make sense yet,

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don't worry too much about it right now

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because we're going to dive much deeper

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into both subnetting and routing in their own lessons

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because we have barely scratched the surface so far.

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Now, the next thing we need to talk about

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is that it's important to realize that IPv4 addresses

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are going to be broken down into classes

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or groupings of ranges that can be used,

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and each class has its own default subnet mask.

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Each class is going to be identified by a letter,

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and there are five classes,

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class A, class B, class C, class D, and class E.

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To identify the class

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for a certain IPv4 address that you have,

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simply look at the first octet.

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A class A network's first octet

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will include a number between 1 and 127,

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and they're going to have a default subnet mask of 255.0.0.0

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This means that the network portion of the address

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is the first octet, and the second, third, and fourth octets

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will all make up the host portion.

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This allows a class A address

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to have up to 256 times 256 times 256 hosts

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on a single network,

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which means we have a total possible combination

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of 16.7 million IP addresses available

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for each one of our class A networks going from 1 to 127.

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A class B network's first octet

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is going to include a number between 128 and 191,

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and they have a default subnet mask of 255.255.0.0

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This means that the network portion of the address

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is made up of the first and second octets,

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and then the third and fourth octets will be reserved

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for that host portion of the address.

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This means that a class B network

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can have up to 256 times 256 hosts on a single network,

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which gives us 65,536 possible host IP addresses

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for each of our class B networks.

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Now, a class C network's first octet

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is going to include the number between 192 and 223,

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and these class C addresses

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are going to have a default subnet mask

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of 255.255.255.0

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This means that the network portion of the address

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is the first, second, and third octets,

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and then that fourth octet

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is going to make up your host portion.

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Because we only have a fourth octet for our host portion,

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this means a class C network will only be able to have

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up to 256 hosts or IP addresses on a single network.

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Now, a class D network's first octet

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is going to include the numbers between 224 and 239.

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Now, a class D address

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does not have a subnet mask assigned to them

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because these class D addresses are considered special,

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and they're reserved for something known as multicasting

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or multicast routing.

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Now, a multicast address is simply a logical identifier

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for a group of hosts in a computer network

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that are available to process datagrams or frames

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intended to be multicast for a designated network service.

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So the actual multicast address

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doesn't align to one specific host,

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but instead it refers to a group of hosts.

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Now, when you think about a multicast address,

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think about it like a group chat.

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You have a group chat name,

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in our case, a multicast address,

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and when you send a message to the group chat's name,

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all of the members of that group are going to get a copy of it.

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Well, the exact same thing happens in IPv4

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when you're using multicast,

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and that's what we use class D for.

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Now, the last class we have is known as class E,

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and class E's first octet is going to include a number

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between 240 and 255,

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and again, class E addresses

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do not have a subnet mask assigned to them

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because they are also special,

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and they're reserved for experimental purposes

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in terms of research and development only.

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This experimental range contains

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about 268 million IPv4 addresses

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that are reserved for what they call, quote, future use.

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Now, over the years, there have been a few proposals

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to reallocate these class E addresses for general use

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because we started running out of public IPv4 addresses

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over time inside of the class A, class B, and class C ranges

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because more and more devices have become connected

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to the internet over time.

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That said, to date, as of the time of me saying this,

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these class E addresses still remain allocated

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for experimental use only,

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and most IP implementations inside of our networks

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will consider any IP inside of the 240.0.0.0

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all the way up to 255.255.255.255 range

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to be considered invalid as the source

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or destination within your datagrams,

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and therefore, the datagram will be rejected

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by your destination system.

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For example, a Windows server or workstation

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will simply refuse to communicate with any device

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that's claiming it's in the class E address space

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because class E addresses should not be used

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in a production or workplace environment.

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All right, now that I've briefly discussed

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the concept of subnetting, I want to go ahead

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and point out that subnetting is just a process

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of taking a larger network portion

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and subdividing it down into smaller portions.

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Now, when it comes to subnetting and subnet masks,

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we have two different types.

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We have classful subnet masks and classless subnet masks.

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A classful subnet mask is one that uses the default

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with a particular IPv4 address.

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For example, if you have an address like 10.0.0.0,

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this is a class A address based on the first octet.

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So if we use a classful subnet mask with it,

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we're going to use 255.0.0.0,

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and this gives us 16.7 million hosts

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inside that single class A network.

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For a class B address,

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the default subnet mask is 255.255.0.0,

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and this gives us 65,536 hosts

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inside of the single class B network.

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For class C addresses, the default subnet mask

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is going to be 255.255.255.0,

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and this gives us up to 256 hosts

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in a single class C network.

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Now, unfortunately, these classful subnet masks

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often create network sizes

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that are way too big for us to use.

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For example, I probably don't need

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16.7 million host IP addresses for a home network,

258
00:11:27,510 --> 00:11:29,280
like a class A would provide me,

259
00:11:29,280 --> 00:11:33,990
nor do I need 65,536 hosts, like a class B provides.

260
00:11:33,990 --> 00:11:35,100
And to take it further,

261
00:11:35,100 --> 00:11:37,530
most of us also don't need 256 hosts,

262
00:11:37,530 --> 00:11:39,240
like a class C would provide.

263
00:11:39,240 --> 00:11:41,220
So instead, we might want to break down

264
00:11:41,220 --> 00:11:43,410
these larger networks into smaller portions

265
00:11:43,410 --> 00:11:46,050
using what's known as a classless subnet mask

266
00:11:46,050 --> 00:11:48,330
through a process known as subnetting.

267
00:11:48,330 --> 00:11:49,920
Now, a classless subnet mask

268
00:11:49,920 --> 00:11:51,720
is going to be used to borrow some of the host bits

269
00:11:51,720 --> 00:11:55,110
from an IPv4 address by reassigning them to a one

270
00:11:55,110 --> 00:11:57,960
in the binary representation of that subnet mask.

271
00:11:57,960 --> 00:11:59,700
And that way, we can increase

272
00:11:59,700 --> 00:12:00,840
the size of the network portion

273
00:12:00,840 --> 00:12:03,060
and decrease the size of the host portion

274
00:12:03,060 --> 00:12:05,280
for a given IPv4 address.

275
00:12:05,280 --> 00:12:07,680
For example, let's pretend I have an IP address

276
00:12:07,680 --> 00:12:11,070
of 192.168.1.0

277
00:12:11,070 --> 00:12:16,070
with a classful class C subnet mask of 255.255.255.0

278
00:12:16,470 --> 00:12:19,980
Now, this gives me 256 IPs for use in my network.

279
00:12:19,980 --> 00:12:23,340
But if I only need to use 64 IP addresses,

280
00:12:23,340 --> 00:12:25,920
I can instead borrow two bits from the host portion

281
00:12:25,920 --> 00:12:28,860
and assign them to the network portion of that subnet mask.

282
00:12:28,860 --> 00:12:33,390
And this gives me 255.255.255.192

283
00:12:33,390 --> 00:12:35,490
as my subnet mask instead.

284
00:12:35,490 --> 00:12:37,830
Now, since the default for a class C network

285
00:12:37,830 --> 00:12:41,190
is 255.255.255.0,

286
00:12:41,190 --> 00:12:42,510
and I'm choosing to use something else

287
00:12:42,510 --> 00:12:44,370
besides that as my subnet mask,

288
00:12:44,370 --> 00:12:47,700
I am now having a classless subnet mask.

289
00:12:47,700 --> 00:12:50,940
This process is known as classless inter-domain routing,

290
00:12:50,940 --> 00:12:54,390
or CIDR, and we usually abbreviate our IP addresses

291
00:12:54,390 --> 00:12:57,000
and subnet mask into one combined notation

292
00:12:57,000 --> 00:12:59,310
which we call CIDR notation,

293
00:12:59,310 --> 00:13:01,620
which we pronounce CIDR notation.

294
00:13:01,620 --> 00:13:06,030
For example, the IP address of 192.168.1.4

295
00:13:06,030 --> 00:13:10,560
with a subnet mask of 255.255.255.0

296
00:13:10,560 --> 00:13:15,560
could be abbreviated as 192.168.1.4/24

297
00:13:16,500 --> 00:13:18,630
if I'm writing it in CIDR notation.

298
00:13:18,630 --> 00:13:19,620
Now, you may be wondering,

299
00:13:19,620 --> 00:13:23,580
why did I put /24 to represent 255.255.255.0?

300
00:13:25,440 --> 00:13:27,900
Well, what we're really doing here is counting the number

301
00:13:27,900 --> 00:13:30,180
of binary digits that are listed as a one

302
00:13:30,180 --> 00:13:32,010
in the network portion of the address.

303
00:13:32,010 --> 00:13:36,090
So if we have 255.255.255.0,

304
00:13:36,090 --> 00:13:39,660
we actually have 24 ones followed by eight zeros,

305
00:13:39,660 --> 00:13:42,240
so we write this as a /24

306
00:13:42,240 --> 00:13:46,350
instead of having to write out 255.255.255.0

307
00:13:46,350 --> 00:13:50,010
This /24 is considered to be a classful subnet mask

308
00:13:50,010 --> 00:13:51,840
for any class c network.

309
00:13:51,840 --> 00:13:54,630
On the other hand, if I have the classless subnet mask

310
00:13:54,630 --> 00:13:58,440
of 255.255.255.192,

311
00:13:58,440 --> 00:14:02,417
I would write this IP address as 192.168.1.4/26

312
00:14:04,980 --> 00:14:07,410
Because, remember, we borrowed two host bits

313
00:14:07,410 --> 00:14:08,790
and changed them to ones,

314
00:14:08,790 --> 00:14:10,800
so they became part of the network bits.

315
00:14:10,800 --> 00:14:13,620
So now, instead of having 24 ones and eight zeros,

316
00:14:13,620 --> 00:14:16,380
I have 26 ones and only six zeros.

317
00:14:16,380 --> 00:14:19,680
This gives me a /26 class C subnet mask,

318
00:14:19,680 --> 00:14:21,090
which would be classless

319
00:14:21,090 --> 00:14:23,640
as a subnet mask for a class C network.

320
00:14:23,640 --> 00:14:25,650
Now, if you're using a class A subnet,

321
00:14:25,650 --> 00:14:27,120
it has to be considered classful

322
00:14:27,120 --> 00:14:29,490
if you have a /8 CIDR notation,

323
00:14:29,490 --> 00:14:33,150
which is a subnet mask of 255.0.0.0,

324
00:14:33,150 --> 00:14:35,130
to indicate that there are eight bits of ones

325
00:14:35,130 --> 00:14:38,070
and 24 bits of zeros in that subnet mask.

326
00:14:38,070 --> 00:14:40,710
For a class B subnet mask to be considered classful,

327
00:14:40,710 --> 00:14:43,440
it must have a CIDR notation of /16

328
00:14:43,440 --> 00:14:47,400
or a subnet mask of 255.255.0.0,

329
00:14:47,400 --> 00:14:49,590
which indicates that it has 16 bits of ones

330
00:14:49,590 --> 00:14:52,500
and 16 bits of zeros in that subnet mask.

331
00:14:52,500 --> 00:14:55,200
For a class C subnet masks to be considered classful,

332
00:14:55,200 --> 00:14:57,960
it must have a CIDR notation of /24

333
00:14:57,960 --> 00:15:02,160
or a subnet mask of 255.255.255.0

334
00:15:02,160 --> 00:15:04,020
to indicate that it has 24 bits of ones

335
00:15:04,020 --> 00:15:06,630
and eight bits of zeros in its subnet mask.

336
00:15:06,630 --> 00:15:09,300
So remember, IPv4 addresses are commonly used

337
00:15:09,300 --> 00:15:12,060
inside of our networks, and these IPv4 addresses

338
00:15:12,060 --> 00:15:15,450
are decimal representations of a 32-bit binary number

339
00:15:15,450 --> 00:15:17,910
that we would write out our IPv4 addresses in,

340
00:15:17,910 --> 00:15:19,560
our dotted-decimal notation,

341
00:15:19,560 --> 00:15:22,110
to represent each one of the four octets.

342
00:15:22,110 --> 00:15:24,390
These IPv4 addresses are further divided

343
00:15:24,390 --> 00:15:26,730
into network and host portions of the address

344
00:15:26,730 --> 00:15:28,470
based on their subnet masks.

345
00:15:28,470 --> 00:15:32,160
Remember that these IP addresses are classified into classes

346
00:15:32,160 --> 00:15:36,420
of class A, class B, class C, class D, and class E,

347
00:15:36,420 --> 00:15:38,850
depending on the first octet in their address,

348
00:15:38,850 --> 00:15:40,080
and then each of these classes

349
00:15:40,080 --> 00:15:42,390
has its own default subnet mask.

350
00:15:42,390 --> 00:15:44,310
When this default subnet mask is used,

351
00:15:44,310 --> 00:15:46,650
we call this a classful subnet mask.

352
00:15:46,650 --> 00:15:48,060
But if you use any subnet mask

353
00:15:48,060 --> 00:15:50,340
that is not the default for that specific class,

354
00:15:50,340 --> 00:15:53,043
we will call this a classless subnet mask instead.