The Building Blocks of Networking

0:00The question of the day, what is networking?

0:03Well, that's a great question.

0:05And that's what this course is all about.

0:08So what is networking?

0:10Well, networking is the interconnecting of devices.

0:13So we could have maybe a computer here, a desktop,

0:16and you could have a laptop computer over here.

0:21There we go, they look kind of similar.

0:23You might have your smartphone over here

0:25that you're working with,

0:26or it could be a larger implementation of that, a tablet.

0:31But either way, we have all these devices,

0:33including things like servers,

0:36that need to communicate.

0:37These are compute devices.

0:39And in order to share information,

0:41they need to be able to send it to each other.

0:43And they do so over a computer network.

0:47So that's the idea of networking.

0:50It allows these compute devices to communicate.

0:54And today we take networking for granted,

0:56basically because most of us have lived with it for so long.

0:59But I remember a time when,

1:01well, this wasn't there.

1:02All we had was standalone devices.

1:06So with that being said,

1:08let's talk about rules and standards

1:12when it comes to networking.

1:14Now, as you can imagine,

1:15we've got all these devices out there

1:17that are wanting to communicate with each other.

1:19And in order to do so,

1:21they're going to need rules and standards,

1:23just like as people when we talk to each other,

1:26like we've got the fellow over here and over here.

1:29And if they want to talk,

1:30well, they need to be able to speak the same language

1:32or communicate in some form or fashion.

1:35If they're speaking a language,

1:36there are rules when it comes to languages.

1:39And in order for people to communicate,

1:41they need to follow those language rules.

1:43And the same thing is true for networking.

1:46There are rules and standards that have to be followed.

1:48We don't want the wild, wild, west happening on our networks,

1:51because then our communications will be very poor.

1:56And it's just not going to be acceptable.

1:58We need to follow those rules and standards

2:01so that our networking works as we expect it to.

2:04And we'll be talking about these rules and standards

2:06throughout the course.

2:08Well, do we need equipment for networking to happen?

2:12The answer is absolutely yes.

2:15We sure do.

2:16We need devices to allow our compute devices

2:21to communicate with each other.

2:23So if we've got these devices over here,

2:26well, in order to communicate over a network,

2:27they need something called a network adapter

2:29or a network interface card.

2:31And we're going to talk about this more in the next nugget.

2:34But the idea is you need something on here

2:37that's going to allow these devices

2:40to either wirelessly communicate to a network

2:43or be plugged in to a network via a wire cable of some sort.

2:48So yeah, we need equipment.

2:49We need network adapters.

2:51And if we're going to talk to devices outside of our network,

2:56well, we're going to need to have some sort of gateway

2:59off of the network.

3:00And this gateway is oftentimes going to be a router.

3:05And that's going to allow us to get off network.

3:08And on network, when we're wired,

3:10we're going to be using switches

3:13in order to allow traffic to pass to other wired

3:17and wireless devices.

3:19So this is kind of the idea that,

3:20yeah, we need equipment.

3:22And we're going to be talking about various types

3:23of equipment and some commands that we can use

3:26on some types of equipment throughout the course.

3:29All right, here's something for you to think about.

3:32Networking, well, it's like the postal system.

3:36And that's because every location

3:40that is going to have mail delivered to it

3:43or data on a network, it's going to need a valid address

3:48so that it can receive and send information.

3:52Just like if we create a letter here,

3:55we're going to write a letter on the front of that letter,

3:58we're going to need to put a destination address on here.

4:03And we're going to put our source address

4:06on the top of the envelope there

4:08so that our postal system will know

4:10where to route that to, where to send it to.

4:12So the idea is, we've got a mailbox down here.

4:15If we want to communicate via the postal system,

4:18we need to have valid addresses.

4:20Well, the same thing is true for a network.

4:23You need to have valid addresses as well.

4:25And we're going to start talking about those addresses

4:27in the next nugget.

4:29So when we send a letter, it goes to our local post office.

4:34So we're going to drop it off there.

4:35And then it gets sent out via mail trucks

4:40wherever it's going to go.

4:41And it gets delivered to the next post office

4:43where then it gets delivered via truck or mail carrier

4:48to the final destination over here, the mailbox.

4:51Well, when it comes to networking, it's very similar.

4:54When we send out data, it's going to go

4:57to something to be delivered.

5:00It could be a switch, it could go through a router,

5:01it could go through multiple devices.

5:04But the idea is then it's going to be transmitted,

5:06just like a mail truck transmits mail.

5:10Well, we're going to be using wireless to transmit data

5:14or wired, either way.

5:16But it's going to get transmitted off to somewhere else

5:19where that data is going to be then forwarded on and delivered.

5:23So the idea of networking being like the postal system

5:27is actually pretty cool if you think about it.

5:29And it will help you to understand it a little bit more

5:32as we go through networking

5:33if you have something to reference it.

5:35All right, so now that we're all on the same page

5:38about what networking is, let's go ahead

5:40and get started on our journey to the C, C, S, T

5:43or Cisco Certified Support Technician.

5:46In networking.

5:48And we're going to kick this off in the next night

5:51by digging into networking addresses.

5:54And there's more than one type, believe it or not.

5:56So I'll see you there shortly.

0:00So let's talk about network addressing.

0:03So when you're at your house,

0:05I'm going to go to the house over here, there we go.

0:07And you're sitting there waiting for your Amazon delivery to get to you.

0:12Here it comes right down the road and it's going to deliver your package.

0:16We'll even put a little bow on it there.

0:18How about that?

0:19So you're going to get your package delivered.

0:21Well, in order to receive that package, you need something.

0:24You need an address so that the Amazon driver,

0:28delivery person will know where to go to deliver your package.

0:32Well, the same is true on a network.

0:34We've got to have addresses.

0:36And in order to connect to a network, to even be part of it,

0:40we need something called a network interface card or a NIC,

0:45also known as a network adapter.

0:47And this is a drawing of one over here on the right.

0:51And this is your standard network adapter that you would see in a computer.

0:56And actually from the outside, you're just going to see a port where you can

1:00plug a cable into,

1:02or you might have an antenna that sticks off of here, something like this,

1:07so that it could be a wireless network adapter.

1:10So you could have wired or wireless, but think of your network adapter

1:15as you're on ramp to the digital highway.

1:19That's how you're going to gain access into the network.

1:22You need a network adapter or network interface card.

1:25Okay.

1:26And that's going to be in all your devices, your smartphones, tablets, servers,

1:30workstations, switches, routers,

1:33wireless access points, all of them have network interface cards in them.

1:38So again, that's how we're going to gain access onto the network.

1:41Now once we're on the network, we're dealing with addresses.

1:44And we're going to deal with two different types of addresses.

1:47The first one is called a MAC address.

1:52And this MAC stands for media access control.

1:56And it is a 48-bit hexadecimal address.

2:03And this is an example of one right over here.

2:07And we see here hexadecimal, that means that we are using numbers 0 through 9

2:12and letters A through F.

2:15There you go.

2:16And it is 48 bits, so you'll see there are actually six fields here.

2:21We've got one, two, three, four, five, and six.

2:26That means each representation in the field is eight bits in length, which is

2:32pretty interesting.

2:34Now let's talk about what these values mean here.

2:38Well, the first three fields here are known as the OUI.

2:46And the OUI is the organizationally unique identifier.

2:52And again, that is the OUI.

2:54Now what is the OUI?

2:55Well, this is a unique identifier that identifies who the maker or manufacturer

3:02of that network card is.

3:04And that's actually assigned by the IEEE.

3:09And this is the Institute of Electrical and Electronic Engineers.

3:13And it's a group that manages the distribution of OUI.

3:17So this first section here, the first half of the address, you can actually go

3:23online and Google OUI Lookup.

3:27And then you can paste in those first three blocks of data there.

3:33And it'll tell you who the manufacturer of the card is.

3:35Now you might be wondering, well, what about the last three blocks here?

3:39Well, those act as more of a serial number.

3:41The manufacturer puts numbers in there so that they end up as part of the

3:46address.

3:47So you have your OUI plus your serial number part, and that gives you your full

3:52MAC address.

3:53Now the MAC address is known as a hardware address.

3:59And that's because that MAC address is actually hard-coded in our network

4:05interface cards that we just talked about.

4:09So on there, you have processing power and you have memory and various other

4:14components.

4:15And your hardware address or your MAC address is hard-coded into the memory or

4:21firmware of your network interface card.

4:24And that's why it's called a hardware address.

4:27And every device that's out there that's on the network has a hardware address

4:31on it.

4:32And this is things from your phones, your routers and switches and access point

4:38and computers and servers and tablets

4:39and anything that communicates on a network is going to have a MAC address.

4:44Now the thing about your MAC addresses, they're used to communicate on your

4:50local network.

4:52Okay, so they are local to your network.

4:55Once your data leaves your network and goes somewhere else, well, that MAC

4:59address gets changed.

5:01As it goes through various other networks.

5:05So that's something to keep in mind.

5:07So that's your MAC addresses.

5:09Next up, the other type of address we're going to talk about are IP addresses.

5:15And here's an example of an IP address right here.

5:18And this is known as the dotted decimal notation.

5:25Now what does that mean?

5:26It simply means that we have decimal meaning numbers and we have dots in there.

5:30And that's what we see, dots and numbers.

5:32Now I say this because when we think about how devices communicate over network

5:38, well, they are doing so using binary.

5:41Meaning ones and zeros.

5:44So if we were to take a look at this IP address right here in its binary format

5:49, well, it's going to look like this.

5:52Yeah, that is quite a long address.

5:56Now these addresses are 32 bits in length.

6:01So if you count these numbers down here, you'll find there are 32 numbers.

6:05And these addresses are used to communicate not only on your local network, but

6:13also to other networks.

6:16So the IP addresses we use for end to end communications.

6:23Whereas when we talked about the MAC address, it's really only used for

6:26communications on your local network.

6:30But IP addresses, hey, those are end to end communications from your sender to

6:35your receiver.

6:37And we're going to get much deeper into IP addresses and subnetting and all

6:41those things.

6:42Right now we're just kind of getting a feel for the lay of the land.

6:45All right, so those are two types of addresses, our physical MAC address and

6:51our logical IP address.

6:55And it is a logical address because we configure it within the operating system

7:00that we are working with.

7:03So yeah, these are not hard coded into any hardware like the MAC address was.

7:07These are actually configured within our operating system.

7:11So that's the basics of network addressing.

7:14In the next nugget, we're going to jump in and start talking about the TCP/IP

7:18model.

7:19So I'll see you there shortly.

0:00The TCP/IP model.

0:03Now, earlier we discussed the need for rules and standards when it comes to

0:07networking,

0:07so that we don't have the wild, wild west of network full of confusion.

0:11We have a nice and orderly network.

0:16That's right, that's what we are looking for here.

0:19And when it comes to networking, as you can imagine, there's lots of moving

0:22parts out there

0:23and we really need a way to kind of organize all of those things to make it

0:28easier to manage.

0:29And troubleshoot when something breaks.

0:31And this leads us to our TCP/IP model.

0:36And this is a way for us to kind of organize all those moving networking pieces

0:41.

0:41And it really is kind of a framework for understanding and organizing all of

0:49the moving parts of networking.

0:51So the TCP/IP model was created by the US Department of Defense, that is the

0:59DOD,

1:00and it was created in the 1960s.

1:04And it has four sections used to group networking activities together.

1:09Those four sections are, as you can see, application layer, transport layer,

1:14internet layer,

1:15and network access layer, all of these.

1:18So let's talk about what these are individually or what they do, starting at

1:22the bottom.

1:23So down here we have our network access layer.

1:26And as you can imagine, this provides network access to all of our devices.

1:32So this is the layer that has the cables plugging into it.

1:38So if you think about this, our network interface card resides here within the

1:43network access layer,

1:45which also means our MAC addresses also reside here because remember they are

1:51part of the network adapter.

1:52They're hard coded on there.

1:54We also have our cables in this layer or wireless.

1:58If we're using wireless communications, all of these things reside down here at

2:03this network access layer.

2:05And this is where all of our bits are sent out across the network, like so.

2:12So that is network access layer of the TCP/IP model.

2:16So if you think about it, this is kind of our on-ramp to our digital highway.

2:22All right, so that's a network access layer.

2:24Let's take a look at the next layer.

2:26And that would be our internet layer.

2:29Now this is where our IP addresses reside.

2:33Remember we talked about the IP addresses and how they are a 32-bit IP address?

2:38And they're used for our end-to-end communications.

2:43And this is also where routing takes place.

2:48We had talked about different hardware and the idea that router is one type of

2:52hardware that we use.

2:54And a router is actually a gateway off of our network.

2:59It helps us to go to other networks, a router does.

3:02And what happens is the router looks at IP addresses and according to its

3:08configurations, will send them to a neighboring device, like another router, or

3:14it could be a local switch.

3:16Or it could be directly to the destination where that data is headed to.

3:23So that is our internet layer moving on.

3:26Next up is our transport layer.

3:29Now this layer is responsible for establishing communications between devices

3:35and managing those communications.

3:37So really it establishes and manages communication sessions.

3:45And this is actually the layer at which we see TCP and UDP reside.

3:55And that TCP is the same.

3:58Famous TCP of the dynamic duo TCP IP that you've probably seen somewhere

4:05written down or being referenced as TCP IP.

4:08Well we talked about the IP address in the last nugget.

4:13Well now we're talking about the TCP portion of that dynamic duo TCP IP.

4:19Now TCP is known as a connection oriented protocol.

4:26And a protocol is simply a set of rules used to communicate.

4:30And connection oriented means that it makes sure that there's someone at the

4:35destination who's willing to accept that traffic or data before it sends it.

4:41So what happens is when you're using TCP IP, your TCP is going to go over to

4:49your destination, which will be this right here.

4:53And it's going to say hey, would you like to communicate?

4:55Can I send you some data?

4:57And if the answer is yes, well then it's going to use its IP address to

5:03communicate end to end and send data.

5:07But if the answer is no, or there's no response, well then what happens is well

5:14communication simply doesn't happen.

5:17And that's the idea of a connection oriented protocol.

5:20It wants to make sure somebody's there to receive the traffic that's coming

5:23across the network.

5:25On the flip side of that is UDP.

5:29Let's talk about UDP.

5:30UDP is a connection less communications protocol.

5:35And that means that in this instance, if we're using UDP and we have a

5:40destination over here, well what's going to happen is this node is simply going

5:47to transmit the UDP data to the destination without checking to see if that

5:53destination is willing to accept the data.

5:54So UDP is more of a send and forget type of communications.

6:01It's not going to be making sure someone is there to receive it like TCP.

6:06Now why on earth would you ever want to use UDP versus TCP?

6:12If TCP is going to make sure that my data gets there, somebody's there to

6:15receive it and it's going to get transmitted and received versus UDP, why would

6:19everyone to use UDP?

6:21Well, there are a couple of shining examples where UDP works better.

6:27Now because TCP does this communication and there's a checking back and forth

6:32that happens and we're going to go through that a little later on, this takes

6:36more time.

6:38Okay.

6:39When using TCP communications, UDP is more of a slim communication protocol,

6:47meaning it doesn't take as much time.

6:49There's not as much going on.

6:51It's very simplified in compared to TCP.

6:54So UDP is actually faster.

6:58And when we're streaming data, think of like a streaming of a movie, okay?

7:05Or could be online gaming, which many of you probably are familiar with.

7:12If you're using a service like a streaming service or online gaming, just think

7:17about this.

7:18If you're watching a movie and the screen pixelates a little bit because the

7:24little data was lost and then the movie continues, right?

7:27Absolutely.

7:28It happens all the time.

7:29Pretty normal.

7:30Do you want that data back that was lost where that pixelation happened?

7:35Well, if you got it back, it would cause you to see the old data or that scene

7:40of that movie out of order.

7:42So if you're watching, let's say, a police chase in a movie and they're chasing

7:46the bad guy down the road and then you get a little pixelation or some data is

7:50lost.

7:51But then the movie continues and the police have stopped the bad guy and they

7:56have him out and they're arresting him, putting handcuffs on him.

8:02Do you want that data that you lost back at this point?

8:06Because if you did get it back, then your scene here would be interrupted with

8:12data or images from a previous scene and it would be really weird, right?

8:18And the same thing for online gaming.

8:20If you're playing a game, you don't want to get lost data back while you're

8:22playing the game because it's going to cause you visual interference.

8:26It's just not good.

8:27We don't want that.

8:28And that's where UDP shines is when we're dealing with real-time data.

8:34All right, so that is our transport layer.

8:39All right, we got one more to go.

8:40And that is our application layer.

8:44And as you can imagine, this is where our applications reside and our

8:50application data, as you can imagine.

8:54And this is where we have our networking happening down here.

8:59And up here we have our applications. So we're going to have translations

9:04taking place at this layer because our data coming up here is in a network

9:09format, but it needs to be translated into some other type of format that your

9:16application is going to use.

9:17Is it an mp4 format?

9:19I don't know.

9:20Is it a JPEG format?

9:23Is it some other type of format?

9:26So your formatting is going to happen there as well as your encryption.

9:30So if you have any encryption that's being used, the encryption and decryption

9:33takes place at this application layer.

9:36So really, it's where your applications are sharing data with the network and

9:40the network is sharing data with your application.

9:44So you got your translation and your formatting and all of that wonderful stuff

9:47taking place right there.

9:49So this is our TCP/IP model. And again, this is more of a framework than a

9:57standard.

9:58And it's really there to help us to organize all of the going ons of the

10:03networking world that we deal with here.

10:07Now, this does really focus on TCP/IP since it's a TCP/IP model, but there's

10:12lots of other protocols out there as well.

10:15And a little later on, we're going to talk about the OSI model, which is

10:18another model, but it's more widely used for things other than TCP/IP.

10:25Yes, it's used for TCP/IP as well, but it also represents other protocols.

10:30So we're going to get into that a little bit later.

10:33But next up, we're going to dive into TCP a little more.

10:38We talked about comparing TCP as a connection-oriented protocol and UDP being

10:43connection less and how they were different.

10:46And we talked about when you'd want to use UDP when we're talking about real-

10:51time data and such.

10:53But TCP is a little more complicated. So we're going to have a nugget just on

10:57TCP.

10:58And that's what we're going to talk about in the next nugget. So I'll see you

11:01there shortly.

0:00In this nugget, we're going to be talking about the TCP 3-way handshake and

0:04something called sockets, but we're going to start off with fragmentation.

0:10Okay, and this is the breaking up of data as it's sent out across the network.

0:17So think of your network data as a train, because if we have a device here, say

0:22your computer and you're connected to the network,

0:26if you go and download a file, let's say you download a 10 megabyte file from

0:35the Internet.

0:36Okay, well, there's something called an MTU right there.

0:42Okay, and this stands for maximum transmission unit.

0:47And it defines how big each section of your data can be.

0:54So again, I'm referencing your network data as a train.

0:59Okay, and there's a reason for that.

1:01Now remember, you're over here downloading this 10 megabyte file.

1:05Well, the way it works on a network is you're not going to get one piece of

1:09data that is 10 megabytes in size.

1:13That's just not how it works.

1:15What actually happens is that data is broken down into several smaller pieces

1:23and it's sent out over the network, and that is known as fragmentation.

1:28So we have this big piece of data here that is 10 megabytes in size.

1:37Well, MTU defines how big each piece of data can be as it goes across the

1:44network.

1:45And Ethernet, which is a standard that we use to send data across a network,

1:52that Ethernet defines the default MTU size as 1500 bytes.

2:02Okay, so that means we would take this 10 megabytes

2:06and divide that by 1500 bytes, and that comes out to 6,667 as the answer to

2:17that.

2:18Okay, so that means our train is going to be 6,667 train cars long.

2:28And again, the process of breaking up these large chunks of data into smaller

2:33pieces

2:34before sending them across the network is known as fragmentation.

2:39Now, these chunks of data that we're sending out, we're going to refer to them

2:42as packets for now,

2:44and you'll see that data at different layers of different models is called

2:48different things.

2:49So we're just going to call them packets for now.

2:52So if we have 6,667 packets as part of our 10 megabyte download,

2:58well, they're not actually hooked together like a train.

3:01They're simply sent out, and they each find their own way to the destination.

3:06And as you could imagine, they get there out of order a lot of times.

3:10It's just the way it happens.

3:12So what TCP does is when it sends these out, it includes a sequence number.

3:20So the first chunk of data will have a sequence number of one,

3:24and then we have two and three, and all the way up to 6,667.

3:30All of that, okay?

3:31And that way, when it arrives at this destination over here,

3:35the destination can make sure to put them all back in order before sending them

3:40up the rest of the networking stack,

3:42going through the different layers all the way up to the application.

3:46So this process of fragmentation happens within networking,

3:52and it's the sequence numbers that allows us to make sure, well, our devices to

3:57make sure,

3:57that they all get put back into the correct order.

4:01So that is fragmentation.

4:03All right, now let's talk about TCP and its three-way handshake.

4:09Now remember, TCP is a connection-oriented protocol.

4:15So it's going to make sure that there is a device at the destination willing to

4:20accept the traffic before it sends it out.

4:24Now, how does this happen?

4:25Well, it does this via the famous three-way handshake.

4:31So we got Bob over here is the client, and Lois over here is the server,

4:36and Bob wants to go out and communicate with the server, okay?

4:41So the way this works is there are three steps in here, part of this handshake.

4:46First off, Bob is going to start the communication process, and Bob is going to

4:53send across something called a TCP-CIN,

4:58okay, just like that, S-Y-N, and that stands for synchronize.

5:02So it's going to send that CIN across looking for a response, but it doesn't

5:08only send that CIN.

5:10Remember, we said that TCP uses something else as well, and that was a sequence

5:16number.

5:17So let's say here we have sequence number five, okay, as this going across.

5:24Well, if the server, Lois, decides you know what, I would like to communicate

5:29with Bob.

5:30Well then, she's going to send, or her device will send, back a TCP-CIN-AC,

5:43just like that, okay?

5:45And that is acknowledging that she received the CIN and would like to

5:50communicate.

5:52Now, that's not the only thing being sent, right?

5:55Oh, absolutely, there's got to be a sequence number in there.

5:58So let's put her sequence number in here, and let's say this is sequence number

6:03103, okay?

6:06But guess what? That's not the only thing going to be sent.

6:09There's also an additional ACK.

6:12So we're going to put an ACK in here, and we're going to say number six.

6:16Now, what does that mean?

6:18What it means is she is acknowledging that she received sequence number five.

6:27So this acknowledgement is actually a plus one, or one more, than the sequence

6:34number,

6:35this one right here, that she received.

6:37So as the sequence numbers come across, the devices will acknowledge with this

6:44type of ACK here,

6:46that it received that previous sequence number.

6:50So that ACK there is acknowledging receipt of sequence number five.

6:56Okay? And that's how TCP makes sure that all the data makes it to its endpoint.

7:04Because if she did not acknowledge this five, then Bob's client over here would

7:10retransmit sequence number five.

7:14Okay? So that is the second part of the three-way handshake.

7:19And lastly, Bob's device will send across a TCP ACK.

7:26Just like that. It's a final acknowledgement saying, "Okay, thanks Lois for

7:31wanting to communicate with me.

7:33I'm now going to start sending you some data."

7:36But of course, what comes along with this?

7:39Well, we've got to send a sequence number here.

7:41So this is going to be sequence number six, since we used five up here.

7:47The next one is going to be six.

7:49Okay? And then we're also going to acknowledge that we received Lois' 103.

7:55And how are we going to do that?

7:57Well, we're going to act for 104.

7:59So we'll put down here acknowledgement number 104.

8:03That means that I received that 103, me being Bob over here.

8:08And that's the TCP three-way handshake.

8:11So it starts with a sin.

8:13Then we get a sin ACK in response, and we send out a final ACK.

8:18Those are the three steps right there in the TCP three-way handshake.

8:24And the sequence numbers are also in there.

8:27And we are also acknowledging those sequence numbers as data goes back and

8:32forth.

8:33That is done because TCBB, being connection oriented, wants to make sure that

8:38all the data

8:39makes it across.

8:40So if, let's say Bob sends some data over to Lois, and she never gets it, she's

8:44not going

8:45to send one of these acts back saying that she received it.

8:49And that means I'm then going to retransmit that data.

8:53So that is your TCP three-way handshake, and how sequence and acknowledgments

8:58work to ensure

8:59all the data gets across the network to its destination.

0:00All right, next up, sockets.

0:03That's right, we're gonna be talking about ports

0:05and sockets here and what they are.

0:09Now, we have talked about TCP and UDP,

0:13how TCP is a connection oriented protocol,

0:15UDP is connection less, okay.

0:18Well, TCP and UDP use something called ports, okay.

0:23And when we talk about a socket,

0:27a socket is an IP address, so we could put 1.2168.10.55,

0:32that's an IP address, followed by a colon and a port number.

0:38This right here is a socket, okay.

0:43So it's an IP address, which is the address

0:46of a system somewhere, a device.

0:48And then we also are adding here a port number.

0:52And it could be TCP port number or a UDP port number.

0:57So what are these port numbers that you talk about, Bob?

1:00(chuckles)

1:01Well, port numbers are ID numbers for services.

1:06And these services run on devices.

1:10Now, if you've ever gone to a website,

1:12which I know you have, you have visited a web server.

1:16And when it comes to web traffic,

1:19HTTP protocol is what we're using there,

1:23that actually uses TCP port 80, just like that, okay.

1:28And there are many, many, many, many, many, many, many,

1:31many ports out there, actually.

1:33Let me change colors here.

1:34There are 65,535 ports in all.

1:39And yes, that is a whole lot.

1:44Now, the first 1024 ports, that is ports zero through 1023,

1:49are known as well known ports.

1:52Okay, so these are kind of predefined

1:56reserved ports, if you will.

1:59And these are defined by IANA, I-A-N-A.

2:04And IANA is the internet assigned numbers authority.

2:09And that's an organization.

2:11And one of their duties is defining

2:15those well-known ports.

2:17So let's talk about some of these common ports.

2:20Well, we looked at TCP port 80,

2:23and that is used for, of course, HTTP over here.

2:27But if we do TCP port 443, that is HTTPS.

2:34So that is our secure web traffic.

2:37And 25, so if we do TCP port 25,

2:41that's your SMTP protocol.

2:44All right, or your SMTP service,

2:47and that's for your simple mail transfer protocol.

2:50So it's for email.

2:52Now, there are a lot of ports, as we see here.

2:55I'm not going to go through all of them,

2:57but we're going to be seeing them throughout this course,

3:00and we'll be discussing more of them as we go along.

3:03This is kind of get you in the mindset of understanding

3:08that ports are how we gain access into services

3:12that are running on devices.

3:15Now, another example I'd like to use is

3:18we have an IP address 192.168.10.55, okay?

3:24And if we were to go to that address here

3:27and communicate with it, think of gaining access

3:31into a building.

3:33And an example I'd like to use is the movie, The Matrix,

3:36where the character is in this long hallway,

3:40something like this, and it has all these doors

3:44just in the hallway, just like this.

3:48So when you gain access to a system

3:50and you're able to communicate with it,

3:52each one of these doors is associated with a port number.

3:58And that port number leads to a specific service,

4:01like our web service or email service.

4:03And that's where the sockets come into play here.

4:07We have our IP address, so we know what client

4:09we're trying to communicate with, but what service are we trying to communicate

4:13?

4:13What protocol is that?

4:15And that's where that port number comes into play.

4:18And that's where the sockets really allow you to communicate directly

4:22with a specific service on a certain protocol.

4:26So that is our sockets and our TCP and UDP ports.

4:31In the next nugget, we're going to look at another type of reference model

4:35for networking, and this one's called the OSI model.

4:38So I'll see you there shortly.

0:00Welcome to the OSI model and the OSI model is another type of reference

0:06architecture or framework that we can use to organize and manage network

0:11communications. Now the OSI model stands for Open System Interconnect. That is

0:20the

0:20OSI. Okay and this is managed by ISO and that's the organization for

0:29international standards. Okay so that is who actually owns the OSI and

0:36manages it but it was originally invented by this French software

0:40engineer named Hubert Zimmerman. Just a little FYI in case you ever come across

0:47a

0:47networking jeopardy question like that. So let's see what this OSI model is all

0:54about and we're going to see here that there are seven layers in the OSI and

1:02we're gonna start down here at the bottom at the physical layers. Let's get

1:05started. Here we go physical. Our physical layer is where the physical

1:12connectivity happens to the network. So here at the physical layer we have our

1:17cabling. So it's our cables or wireless. Okay and at this layer data is known

1:26as

1:27bits. Okay that's our ones and zeros our bits are being sent out across our

1:36physical network. Now let's talk about some hardware as well. Okay so when we

1:43have hardware on our network and we're gonna actually talk about some different

1:47types of hardware in this skill and where it resides in the OSI model. So at

1:51the

1:51physical layer we have our cabling or wireless and that's some hardware right

1:56absolutely. Now something else that resides at the physical layer is our

2:02network interface card. Now the network interface card is a little tricky

2:06because

2:07it actually resides at the physical layer and the data link layer which we'll

2:13see next and that's because our NIC is where our cables plug into or our

2:19wireless signals are sent and received and that's why it resides at that layer.

2:24Okay so that's our physical layer just think of that as your physical network.

2:28What things touch and that's your physical layer. Next up moving up we have

2:33our data link layer and as we said our network interface cards reside at this

2:38layer as well and that's because this is where our MAC addresses reside. Okay

2:45and

2:45the data link layer is actually split into two sub layers. One is the MAC two

2:53is

2:53something called LLC and this is our logical link control and this is the

3:01mechanism that helps to manage communication. All right and when we're

3:08working at this layer data, let me change colors here, data is known as frames.

3:15So

3:16we see that data goes by different names depending on which layer that you're

3:21working with because if we go back to our physical layer down here we saw that

3:27data is just simply known as bits but when we get up to the data link layer we

3:32see that our data is known as frames and this is where our network interface

3:37card resides but remember our NIC also resides over here on our physical layer

3:44and that's because that's where the cables plug into and then as we go back to

3:48our

3:48data link layer our MAC addresses reside at the data link layer and our MAC

3:52addresses are also hard-coded into our network interface card. And one more

3:59thing I want to talk about at the data link layer we know that as far as

4:02hardware

4:03goes at the data link layer we have our network interface card remember that

4:10resides at both our data link layer and the physical layer but we also have

4:14switches. So our switches that we plug into on our network those reside at the

4:20data link layer because switches use MAC addresses to make switching decisions

4:25and access points. Those wireless should put that on there wireless access

4:31points

4:32those are also at the data link layer so there you go that is the hardware at

4:39the

4:39data link layer moving on up next up is our network layer there we go and at

4:47the

4:47network layer this is where our IP addresses reside okay that's very

4:54important and this is where routers reside that's our physical network

5:01appliance routers or it could be a virtual router as well but either way

5:04routers reside at layer 3 because routers provide us routing services and

5:11routing is based on IP addresses so these really go together like peanut

5:17butter and jelly. Now you might be wondering hey what is data known as at

5:25this layer well data at the network layer is known as packets there you go

5:32packets it is. Alright super now I'm to the next one on to our transport layer

5:39now transport layer this is where TCP and UDP reside so that means because we

5:49talked about TCP and UDP having ports this is where our port numbers reside

5:55absolutely and this is where our TCP 3-way handshake happens because that's

6:06where TCP resides and of course you might be wondering well what is data

6:10known as well at this layer data is known as segments and another thing is

6:18since we're using TCP at this layer this layer ensures that the data packets

6:25arrive accurately and it ensures that they are put in the correct sequence so

6:31that they can be sent right up the rest of the OSI. Alright next up is our

6:40session

6:40layer now the session layer manages end-to-end communication so it's

6:49responsible for going through the process of setting up a communication

6:55session and then maintaining that session and then tearing down that session

7:03when communications is finished okay so the session is all about managing the

7:10communication session between devices and data at this layer is simply known

7:18as data that's right for the rest of the way up the OSI data is simply known as

7:24data pretty straightforward there next up is our presentation this is where

7:31data translation and formatting occurs so this is we're going to see things

7:36like your mp4 and jpeg and all your other types of different file formats

7:42and this layer also handles encryption and decryption so that is your

7:47presentation layer and then lastly we're on to our application layer and this

7:53is

7:53where application protocols reside so those protocols that we talked about

7:59earlier we talked about HTTP and HTTPS and SMTP for email all those are going

8:07to reside up here at the top of the application this is where we have file

8:12sharing taking place this is where we access databases so database access this

8:20is where messaging takes place and this kind of basically injects data into our

8:29apps and that's the application layer all right so that is the OSI model and

8:38it's seven layers and what resides at each layer and kind of how things work

8:45and if you're wondering how you can remember the order of the OSI's seven

8:50layers I've got a couple of mnemonics for you the first one is please do not

8:57throw sausage pizza away and that is for your physical data link network

9:04transport session presentation and application layers so please do not

9:09throw sausage pizza away and if you don't like that one got a second one for

9:12you and this one is all people seem to need data processing and this one goes

9:20from the top down we have application presentation session transport network

9:25data link and physical so there you go a couple of mnemonics to help you

9:29remember the seven layers of the OSI model and now that we've seen this OSI

9:34we know what it is in the next night we're gonna see the OSI in action so see

9:39you there shortly

0:00All right, let's see the OSI in action.

0:03So over here we have Bob,

0:06and Bob is gonna send some data over here

0:08to Lois at the server.

0:11So Bob uses whatever application he's using,

0:14this could be an email, it could be a file transfer,

0:17whatever it might be.

0:18He wants to send something over to the server,

0:20so he does so in his application of choice,

0:25which then generates the application layer data.

0:29Okay, and as that data goes down the OSI,

0:34we're gonna follow it throughout its journey

0:37and then across the network over to Lois

0:39and back up the OSI on Lois's side.

0:43So right now we have our data

0:45and it's in an application format,

0:48so put app format, there we go,

0:53whatever that application is,

0:55and then that data is passed down to the presentation layer

0:59and here is where that data is formatted into binary.

1:04Okay, 'cause that's the computer speak,

1:09that's where we're gonna transmit that data in,

1:11then that data gets passed down to our session layer.

1:16Okay, and at the session layer,

1:18we know that the session layer's going to go ahead

1:20and set up end-to-end communications with Lois,

1:29or her device that is,

1:31and then at that point,

1:33that data is handed down to the transport layer

1:36and once it gets to the transport layer,

1:39if that application's using TCP,

1:41so let's say it is, it's going to then

1:44do the TCP three-way handshake, excellent, all right,

1:49and it's actually going to do something

1:52called adding a header.

1:54So what it's going to do is add a header to the data

1:58and it's gonna provide some TCP information.

2:00So the way this looks is we have our original data here,

2:05this is the data that came from the application.

2:09So here we're going to add what's called the header

2:12and this is going to contain TCP information there.

2:16Okay, and then at that point,

2:18the data is passed down to the network layer

2:21and here is where the IP address resides

2:24and we're gonna see a routing take place

2:27and so on and so forth, but what happens is

2:30we get a network layer header added in,

2:33so there we have our network, here's our TCP

2:35and then here's the original data, so let's fill this in.

2:38So here we have network-related information,

2:42this is TCP and this is the original data.

2:47So you see we're adding headers on here

2:49and adding of headers is known as encapsulation, okay?

2:55Super, so then as the data is passed down

2:58to the data link layer, here we're going to add

3:01a data link header, we still have our other information here,

3:06so let's put in here, we'll say Mac for like Mac address,

3:11which relies at the data link layer

3:14and we have our net information for a network layer,

3:17TCP and our original data, all right, super.

3:22And so here at the data link layer,

3:23the device is gonna look at the Mac address,

3:25it's going to be deciding on what to do with that,

3:28is it on network or off network,

3:30it's gonna pass that down to the physical layer

3:32and here's where we end up converting all of this information

3:37into ones and zeros and we're sending them out

3:42on either the cable or over wireless.

3:47So that is the process of encapsulation,

3:51as that original app data is going down the OSIMO,

3:55then the exact opposite happens.

3:57Once it gets over here across the network

4:00to lowest in the server,

4:01well that data is received, those ones and zeros

4:05here at the physical layer and then it's passed up

4:09to the data link layer.

4:10And here we have, let me draw over here

4:14the encapsulated data, we have here,

4:18there we go, just like that, our two, three,

4:22original data, but we also have our Mac headers,

4:27for layer two header, we have our network layer header,

4:31we have our TCP header here,

4:34and then we have the original data.

4:36So what happens here is the layer two data link layer

4:40will take a look at this information in the Mac header

4:43and then process that data and send it up to the network layer.

4:46Now at the network layer,

4:48we're not gonna have that Mac header anymore,

4:50it's just going to be our network information here,

4:55our TCP and the original data,

4:58because the data link layer removed this Mac header.

5:03And so then at this point,

5:04the network layer is going to receive this data,

5:06it's gonna verify the network information here

5:08in that header that we just talked about,

5:12and it's gonna strip that off

5:14and then pass it up to the transport layer.

5:16At the transport layer, as you can imagine,

5:19the same thing's gonna happen here,

5:20we have our TCP header and then our original data.

5:25Okay, the transport layer is going to go ahead

5:27and strip off this after it reads that information

5:31and decides what to do with it,

5:32because at this layer, we're gonna have TCP information,

5:34including the port number.

5:37Remember we talked about ports earlier and sockets,

5:40well that port number's going to reside

5:41in that TCP header down here.

5:44Okay, and so it's gonna strip that off

5:46and it's gonna send that data right up to the session layer

5:49over here, we have our regular data,

5:52and the session layer again is managing

5:54the end-to-end communications,

5:55this will then be passed up to the presentation layer.

5:58And here the data that we have, which is binary,

6:01it's gonna be converted into formats for an application,

6:04and then passed up to the apps themselves.

6:07So the process of removing the headers,

6:10like we see here, is called decapsulation.

6:14So here we see how encapsulation and decapsulation happens

6:19as data goes through the various layers of the OSI model.

6:23So this is the OSI in action,

6:25so in the last night we talked about what the OSI was,

6:28what happened at each layer, what equipment was at each layer,

6:30what data was referred to as each layer,

6:33but here we see that as data goes through these layers,

6:36going down and then back up at the remote side,

6:40that some of the layers,

6:41actually starting here with the transport layer,

6:44add a header.

6:46So that's our transport network and data link layer,

6:48I'll add a little bit of extra data to our packet.

6:53So this is information related to each layer

6:56that will help ensure that that data is accounted for

6:59and received by the correct endpoint

7:02and processed correctly as well.

7:04And that process is encapsulation,

7:07and then at the other end, we decapsulate it,

7:09we pull those headers off and use that information

7:11to make sure that that data is processed correctly.

7:13So there you go, the OSI model in action.

7:16And that wraps up this skill.

7:18So next up, we're going to do a validation,

7:20got some review questions to see

7:23just how well you retain this information.

7:26So I'll see you in the validation shortly.

0:00All right, here we are in our validation.

0:02So we've got a few review questions that we're going to go through and see just

0:07how well we

0:08retain this information.

0:09So question one here, it says place the four layers of the TCP/IP model in the

0:15correct order

0:15from bottom to top.

0:17So this means from the bottom will be number one.

0:21So what's at the bottom of the TCP/IP model?

0:25If you remember, it was network access.

0:29So network access should be number one that's at the bottom.

0:32Okay, so what came after network access going up?

0:36Because this is where we access the network.

0:38Well we need an IP address to communicate over the internet.

0:42So this is actually number two there.

0:45Because we started with network access, where we gain access into the network.

0:49But then as we go up, we needed an IP address that happened to reside at the

0:54internet layer.

0:55And then we need some communications and that's the transport layers.

0:59That's number three.

1:00And that leaves the application layer all the way at the top as number four.

1:05So that is your answer there.

1:08Now let's move on to question number two.

1:10Ooh, here we go.

1:11Place the seven layers of the OSI model in the correct order from bottom to top

1:16.

1:16All right, so let's see here.

1:19What was at the bottom?

1:20If you remember, we had some new monics to help us remember this.

1:23I prefer, please do not throw sausage pizza away.

1:27That starts at the bottom.

1:28So P was for physical.

1:30So physical is number one.

1:32So that was our physical.

1:33If we do, please do not, well the do is for data link.

1:38So that's number two.

1:40And the not is for network, which is layer three.

1:43There we go.

1:44Then we come through throw sausage pizza away.

1:47So the T and throw is for transport.

1:50That's number four.

1:52And then we have our image.

1:53It's our session.

1:54That's for doing our Indian communications management.

1:56That's number five.

1:57And then pizza.

1:58Well, we already know that this P is for physical as at the bottom.

2:03So this P must be presentation.

2:06That's right.

2:07And then lastly, application is at the top.

2:09So that's your, please do not throw sausage pizza away.

2:11OSI model layers in order from top to bottom.

2:15All right, question number three.

2:16What type of address resides at the data link layer that OSI model?

2:19So if you think of the data link, remember the network of data link.

2:22The data link layer is a data link layer.

2:24And it's a data link layer because a certain type of address is hard coded onto

2:29the network

2:29interface card.

2:30And that's your hardware address or MAC address.

2:34There you go.

2:35The MAC address resides at the data link layer of the OSI model.

2:39Moving on to number four.

2:41What does TCP use to ensure packets are put back into the correct order when

2:47received

2:48by the destination?

2:53So remember we talked about those getting broken down via the process of

2:58fragmentation

2:58into many little packets that go across the network.

3:01And how did TCP make sure they were able to be put back in order?

3:05It used the sequence number.

3:08That is correct.

3:10Excellent.

3:11Moving on to number five.

3:12Final question.

3:13UDP is a connection oriented protocol and TCP is connection less.

3:17Is that true or false?

3:20That's right.

3:23TCP is connection oriented.

3:25That's where that three-way handshake comes into play.

3:28UDP is connection less.

3:30So those are our five review questions as part of our validation challenge.

3:35I hope this has been informative for you.

3:37And I'd like to thank you for viewing.