Introduction to Computer Networking with a Hands-on Connectivity Project | Andrew Mehri | Skillshare

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Introduction to Computer Networking with a Hands-on Connectivity Project

teacher avatar Andrew Mehri

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Taught by industry leaders & working professionals
Topics include illustration, design, photography, and more

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Taught by industry leaders & working professionals
Topics include illustration, design, photography, and more

Lessons in This Class

8 Lessons (1h 22m)
    • 1. Course Objectives

    • 2. Where to Find Cisco's Packet Tracer? (Simulator used for this course)

    • 3. Introduction to Packet Tracer: How to use it!

    • 4. Connect Two Devices

    • 5. Inspect the Communication

    • 6. Connect Multiple Devices

    • 7. Monitor Frames and Start of Project

    • 8. More Simulation to Support the Project

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About This Class


This course will use simple examples to demonstrate how computers can exchange information.  During this course, you will be led in a step-by-step fashion towards building simple networks and then analyze how communications are established, maintained and terminated.  This networking course is meant for mere mortals that want or are studying computer networking, and would like a foothold small project to get started.  Some basic knowledge of the OSI will be helpful, but you can still follow along and then that model will make even more sense if you want to study it some other time.

Some examples will use ICMP messages and the course project will include a connection oriented application HTTP using TCP.  Packet Tracer will be used to simulate the networks and examine frames and packets during the exercises and the course project. 

For the simulator, you will need Cisco's Packet Tracer.  To install Packet Tracer and test it out before you start the project, use the three last video lessons and replicate their described steps.

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Andrew Mehri


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1. Course Objectives: Greetings, I'm Professor Andrew Marry and welcome to our computer networking course. For our networking course, we will build simple networks to understand how devices communicate. To accomplish our goals. We will work together to connect and configure devices to reside on a network. We will test and verify connectivity. Then finally, run a specific feature of our simulator. Inspect frames and packets sent across the network. And that will lead us to our course project. Well, you will redo all of these tasks. But this time it will be specific to connecting to an HTTP server, which is really a web server. To accomplish these tasks, you will need a simulator. And we will have three videos on where to get the simulator, how to configure it. What are the features of that simulator? And we will do a simple example using that simulator prior to getting into the core concepts that this course will cover. These are suggested steps that you should consider to complete your project. These slides will be available for you to re-inspired act and go through this list. If you need to follow it exactly as it is. But you are free to complete this in any way you want, as long as you obtain the main objectives or achieve them. The important thing is that you draw a conclusion from observing the simulator results to make sure that you understood the concept of connectivity. This slide here has some of the concepts covered in this course. Since we will be connecting to a web server. So the HTTP protocol is the, will be utilized the ICMP for testing connectivity. We're also be utilized. The AARP, which is an address resolution protocol, would be used to make sure that n devices know about other devices within their own network. Tcp will be a form of connectivity, which is connection-oriented in our case, that will be related to the application HTTP, which is when you connect to a web server. The methodology in which you can act will utilize either TCP or UDP, and our case will be TCP. These concepts will be covered in another more in-depth course on the transport layers and the application layer. And we will go into the insides of the OSI reference model. For our course, we will focus on layer two and layer three in terms of inspecting frames and packets. Are you ready to learn? I know you are. Let's go ahead and do it. 2. Where to Find Cisco's Packet Tracer? (Simulator used for this course): Welcome back to our networking course. To proceed with their scores, we will need a simulator. With that simulator, we will simulate hands-on labs that will cover the learning objectives needed for this course. The website from which you can download this application is called net a It is from Cisco. This is their training website. And you could register for our example to learn about how CCNE a and works for example, or CCMP, one of their famous certifications. On top of that, they have other training as well, including IoT programming. And as you can see, they're listed right here. What we're interested in right now is the Packet Tracer. So if I click here, okay, it gives us an introduction as to what Packet Tracer is. And definitely it is a free package, however, you need to register. Okay? So if we want to look at the actual course itself associated with Packet Tracer offered by Cisco. That's a ten hour long series of lectures that help you understand how to use Packet Tracer so you can effectively use it. During lab time. In our course, we're going to be using a lot of these features that will be described in these ten hours, 10 hours training. I highly recommend that you go through it. If you don't have time. It is not the end of the world. We will be covering some of that stuff throughout our lectures as we go in as needed. Okay. All right, so I hope you sign up for it. You downloaded, it's free. However, every time you need to use it, you're going to have to login, okay? And there are two ways you can log in into Packet Tracer, either as a guest. But that will have limitations in terms of how many times you can save to a local file on your hard drive versus a fully authenticated a login based on your credentials. That will give them a lot more flexibility. I highly recommend again that you fully log in as you replicate some of the labs we will be presenting throughout this course. I will see you later for a demonstration, a quick demonstration what Packet Tracer looks like and the version that we will be using. See you then. 3. Introduction to Packet Tracer: How to use it!: Okay, Welcome back. And I hope by now you have downloaded Packet Tracer and you're ready to run it. And if you do, forget to log in, in my case, I have already done so. And as you can see, I'm going to move my mouse to the icon right here and it shows I have Packet Tracer version 7.3. So I'm going to click on that. Okay? And what I have now is what we call the logical view. This is the default view right away that is offered to me to go ahead and put devices, network them. And then we can do some analysis either in real-time or in simulations. As you can see, I have a couple buttons here that allow me to do a few things. We will see this throughout our course and how to use one or the other. Okay? So again, I have, I am in a logical view right now, okay? What does that mean? That means I can logically put some computers regardless where they might be physically. So it is basically a drawing board where I can put my computer's, my networking devices, my connections. Let's do a quick example of that. So as you can see here, I have categories. Within those categories of devices. I'm going to have groups, sorry if I click here where I have either a networking devices or Android devices, let's click on n devices. Notice I have within that groups, okay, I am going to go for the group that has computers or IP based devices, such as your laptop, your computer, or a server. Okay. Notice you even have an IP printer, an IP phone, et cetera, okay. Including TV, right? So let's say I pick a computer by clicking on it. And then go to your workspace here in the logical view and just release. Okay, or you can click here, you get your PC right here. Prior that I had another PC that I deleted. So you can actually delete this if you don't want it here. You can go back here and click on Delete right here where you have an X, okay? And then bring your mouse here and that will remove it. Let's bring the PC again and put it in. And notice every time it remembers really in sequence which one supposed to be putting in here. This does not matter if it put PC3 or 20. It's up to you later on to rename it anything you want. And notice as I'm hovering my mouse on it, It's given me some characteristics of this computer. Since this course will be about networking, and this simulator is about networking, those are the parameters that I'm getting. It's giving me the MAC address of this device. It's also telling me that the IP version 4 and IP version 6 addresses are not set for the Ethernet or the Bluetooth for this device. And let me show you here some more. Nothing is set on it. Okay. So that's fine. Can we do the same with the server? So let me just get a server here. Okay? And I have done nothing also with the server, but it has its own, The only thing that it has its own MAC address, which we call the physical address. Okay? All right, so I have these two devices. Can I connect them? And the answer is yes. And since they're unlike devices, their layer 3 devices, you're going to take a crossover. You're going to go from here, you're going to click here. And notice the ports that I'm afraid. I'm going to pick Fast Ethernet and go to Fast Ethernet here. You can see I have green dots here, which means the, this is probably the proper cable for these connections. I haven't set these computers to talk to each other yet. That is not the objective for this lab right now. But we can see that in the logical view we can have devices connected and then we can configure them. Okay, so let's suppose I wanted to configure the computer to have some sort of an identification. Logical identification is far as its IP address, you click on the computer and notice the window you're gonna get. This is the same thing if you clicked on the server as well. So let me click on the server, you get the same thing. And I only that let me make this a little bigger here. You could see the back of the survey here, how it looks like physically as a picture. You can see that it's on right here, the light is on. And let's go to the computer and do the same thing and see. And you can see also that you have a desktop. It looks like a tower and it's on so you can actually turn it on or turn it off, okay? And within the desktop app, you can go to the command prompt. And right here you can see a typical command prompt where I am on the CGI if right. So as you can see, and I could do a DIR. So these are DOS command that you can run Right away from here. Okay? So this is a lot of fun. So think of these as actual computers that you can interact with and run some commands. So for example, let me go back here and go to the command prompt here. And for example, type something like ping 192, 168 dot 10 No.1. Now, there is no such device right now configured with that address. Obviously, I am going to fail at retrieving anything, but it is actually running the ICMP message protocol. But it's as high as you can see, it's timing out, which is exactly what it would do in real world if your computers are not configured and your network is not configured. Okay? So that's from a logical point of view. You also have a window for the physical point of view. As you can see here, you have a home city, have a map, literally a map here. And we can log in, I'm in, zoom in down to corporate office. And notice our PC is right here, PC3. And it's connected to some sort of a closet. And we're let's click on the closet and see what's in it. And notice I have a server on a rank. Okay? This is neat. You can, and here's the cable right here. So you can actually take out the Internet and plug it back in. So you can physically do this as if you're in the lab. Okay? That is one major improvement. There's version of packet tracer has over its predecessors. So I hope to see you next where we're going to do our first lab. 4. Connect Two Devices: Okay, welcome back. Think about why do you need a network? And a computer network to be more precise. Well, if you had one computer that can do everything for you, you're sent. Unfortunately, that is not reality. So to expand your computing capabilities, you typically connect through your Wi-Fi or three a LAN physically to some sort of a router at home or at work. Where from there you have a gateway to the world and you have access to websites, services, etc, including signing up for this course. So it is an important aspect of our life. Now. We used to go to the market. We still do, but not now. We probably spend more time purchasing stuff online, then going to a store. And that is the reality that we're living in. So we need to understand how do we access a service from, let's say, a local computer or from your phone. So let's simulate that scenario with a computer connecting to a server. So notice here I clicked on the group computers, so I'm just going to pull out a computer or laptop or any of these devices that are available for the public. Servers are a little more expensive. We're going to leave that for the service that you want to access. So let's take a PC and put it right here. Okay? So this computer here, I can turn it on, turn it off. I can install applications in it. If as long as those applications can run on this computer without needing the Internet, then I'm fine. However, like I said before, most likely you're going to be wanting to download files. You may want to play games online without people, et cetera. So you need to access some form of a service that will allow you to take advantage of your expanded the program, expanded capabilities. What Let's put a server, let me put a circle right here. So let's say we want this computer to access this server. The simplest form of communicating between these two is to put a link between them. We're going to put a physical link. So let's go over here. And we're gonna do our crossover. And again, we will have a lesson to explain what crossovers are. A crossover cable that connects with this Fast Ethernet to this Fast Ethernet. Now, this is in its simplest form. That means is there more to it than that? Absolutely. What if I had more than one computer? What if I had more than one server, then this architecture will not work. And the fact that you have one port when Ethernet port on either one of these two devices limits you in terms of connectivity. This is the only possible connection between these two devices. And at this stage, these two devices better be in the same area, in the same room. Speaking of which, there must be also, they must be also in the same domain, which means they have to be on the same network as it stands. Now, most servers that you will access through the Internet are going to be in the different networks. What that's another lesson that we will tackle once we understand the hierarchy, how networks work, or how they are distributed through those hierarchies. At this stage, we hierarchy is fairly simple. Okay? So it's one link to end devices. Can they talk to each other? Not at this stage because if I highlight any one of these computers, none of their identifications are set other than their MAC addresses. So if you look at the MAC address, for the Mac is the physical address. But that's not enough for these two to start negotiating or exchange data. We need a logical address called an Internet Protocol address or IP address. And we have to make sure that when we assigned that IP address, that these two devices have unique IP addresses. They cannot Clash by being the same. However, they have to belong to the same network, which means in the same broadcast domain. And again, we'll have a lecture on broadcast domain and collision domain and understand the difference between them. At this stage, we want them to be in the same broadcast domain. And the mere fact that we have a link between them, they are in the same collision domain if we're using Ethernet. So let's go ahead and set up the IP address for our server so we can go over here. And the way to do this, you got to click on it and then you click on config. And notice you have Fast Ethernet 0 right here. And don't mind these, we're going to be looking at these in another lab. So for now you go straight to Fast Ethernet and set up an address for now, take my word for it. Just set the address as I give you 192, 168 dot 10 dot one. Now this is what we call a private address, Class C. Now notice that the subnet mask will be automatically generated based on the way it is subnet it. At this stage, again, don't worry about those details. Just make sure you're enter the IP address the same way I just did. So 192, 168 dot 10 dot one. Okay? So this will be the logical address for this particular computer. So let me close here, let me highlight again, go over it. And you can see now that it has an IP address of 192, 168 dot 10 dot one, the slash 24 next to it. Is the subnet mask, that's your, let me go back here. That's this 255, 255, 255 dot 0. It's another representation of this mask here. And again, that will be for another lesson. Good. Now we're gonna do the same thing for the PC. So that way they are both in the same network. We're going to go too fast Ethernet and we're gonna do 192, 168 dot 10 dot t2. Notice the other one was dot one. This one is D2. The last, what we call octet. In this particular configuration is for the host ID, which means we have two hosts. So let me click here and notice they're using the same mask. So when we say host or n nodes, we could use them interchangeably. So we have two hosts or two nodes. And let me highlight here, this one is D2, 192, 168 dot 10 dot t2. And let me highlight this guy, and this one is 192, 168 dot 10 dot one. Okay? We will learn from the IP address and how to distill the network part of it and the host bottom it right now One. And to identify which hosts we have. So they cannot be dot one, dot one or D2, D2, Kitoi. They have to be different. Excellent. Now, can we have these computer spring each other to make sure there is connectivity? The answer is yes. Let's click on the computer and let's go to the desktop and go to the command prompt and actually ping the other computer. Pinging means I am sending it an ICMP message out to see if I'm going to get an echo back, right. So it's going to be I'm going to get a reply that says a yes. I'm right here. And so it's like Hello. Hello. Okay, so that's what a ping on an ICMP message, but you're going to have to enter the address of the destination where you want to reach 168 dot 10 dot one. Remember, this is D2. So we want to reach that one. So let's see if we can reach it. And notice we're getting replies. This here means we are getting replies, okay? And we will in another lecture, break down all of these messages as to what they mean. So that means, and this is, I'm going to highlight this. I have 0 losses. Everything for packets were sent forward, received. So everything is good in terms of the link and its health, the configuration is correct. So we're gonna do the same thing from the server. We could do the same. So I'm gonna go to desktop and I'm going to go to the command prompt. I'm going to ping the other way around, which is 192, 168 dot 10, dot, dot t2 this time, okay? And notice I get a similar message. Okay? And again, 0% losses. Which means the link is good. Now, the fact that we have a server, I would like to use it for sampling. So let's click on the server again, and let's go to services. So in services in this column right here, you've got all sorts of services you can use. What do you want the server to do? It could be a DHCP server which dynamically assigns IPV4 addresses to devices connected on that network. Could be a DHCP version six. It could be a TFTP server, et cetera, even an e-mail server. I'm going to do HTTP. Http means it's a web server. And notice it has an index page, it has an image. So it has a whole bunch of HTML files that it's hosting that we want clients to be able to reach it. Smart FAQ, we can edit the file right here. And we can see that we have an HTML file. That if we have a browser, we will be able to interpreted without these tags right here and see it as a webpage. Well, which web browser is going to allow us to access this on the client side? Which one? Well, the PC is going to be the client for this service. Well, let's see. So let's go over here this time. You're not going to run this from the prompt. You're going to run it from the web browser over here. So I'm going to click on web browser and notice it's asking me for a URL. Now, typically, if you are going to enter a URL, you would do WW dot whatever the name or the resolved name for that website At this stage, There's no DNS up there or a domain name server that this IP address for this, for this server has not been mapped to any name. So the way to access it is by using the IP address of y. Well, let's do that. 192, 168. And you type that as if you're typing, right? So same thing, but you're typing the actual IP address that you want to reach, 10 dot one. Now let's see what happens. And there you have it. Remember those texts were the tags. This is when it had in it. Okay. And it runs just like a website. So I can go to Image page. You can see here, I can, back from here, I can go to this image. And back from here, I can go to copyright. So as you can see, there are links to other pages from here, right? And I can forward link. Here you go. You can see from this address slash copyright that HTML. So it's as if it's a, another file from that point other than index. This is what you're getting. So typically when you go to this link here, which is an IP address, you're opening the index page that's stored in that directory. Okay? So the server PT is acting as a web server and we're able to access it through the computer. So this is the basics of networking right here as to using the service available by that server that you have access to. 5. Inspect the Communication: Okay, welcome back everyone. Let's look at the scenario we started last time, but this time what we will do is we were going to run the simulation. We want to see how frames move from one node to another and what exactly is inside that frame. And in particular, if, let's say we use an ICMP message like we did with ping. How does the frame look like in what is involved with that frame? Okay, So this will be a good exercise to see the simulation part of Packet Tracer. Okay, So to get started, let's review quickly what we have here. We have a computer PC and let me just hover over it. And you can see that it has the address 192, 168 dot 10 dot T2. Okay. So jot that down in your notes. So you know that's that computer. And it has a MAC address of 0004984, C, D, a, C. Okay, Good. We're gonna do the same thing with the server here. So at least we know where we're starting with. We have an IP address of 192, 168 dot 10, dot one, and the Mac address of 000 3000, I mean 300, a three-to-one, C7, C6. See, fantastic. Now let's put in an action. So before what we have done, if I go to this computer, for example, and I go to the desktop, and I go to the command prompt and I hit a ping, 192, 168 dot 10 dot one. So I'm trying to ping the other computer or the server. Let's see what happens. Okay? And as you can see, we're gonna get a reply. Everything looks good. Okay, now we can do this visually as well, right? So as you can see here, we have 0 losses. Now we could do this visually in this manner. Do you see where you have an envelope right here. So I'm going to take an envelope, put it here, and then here. Now, what that means is I am taking a frame that will have the source as our computer that is in dot t2 going to dot 1. Remember those IP addresses and the host octet, right? And that's what I physically did. So notice now we have a new line here. Remember we're still in a real time that shows that the ICMP was successful. This is equivalent to having typed ping 192, 168 dot 10, dot one. Okay, So now we did it visually. Now, if I do it again, let me just go from here. To here, you can see that I have a second line here under this window here that shows that everything was successful. And notice that the source was P7, the destination was server 2. Let's do it the other way around. So you get an idea. So let me go from here to here. And notice now the source is the server and the destination was P7. And it was basically a simple ICMP message that requires a reply. Now we don't see that reply here. There's not enough resolution in this simulation. But it's so we want to see that so that we're going to do in this material. Notice here I hit delete, so I removed all of these scenarios and I'm going to now go to simulation right here. Okay? So I clicked here. And now we can stop through the messages as they go from one place to another. And then if there is a reply, we get to see that as well until it's completed successfully. Okay, So remember this is a message that requires an echo back. Once you receive the app group, it's done. If everything is fine, then it completed successfully. All right, well, let's get started. So you do the same thing. Take so click on this envelope, click here, and then click here. Notice that the envelope remained right here because we're going to be stepping through this. So we're gonna do this one step at a time. So notice we haven't completed anything. It's in progress right here below. Okay. From P7 to server 2. It still is. It's an ICMP message. Okay. So can we look at the details associated with this message, with what's in the envelope like, let's click there. And notice it's an outgoing message right here. And the beauty about this is this here, this view is that the OSI model view. What layers of the OSI model are being involved with this ICMP message at this stage. Okay, so remember we're sending, but we are in simulation mode, so we're like frozen in time where that frame, it's still held by p, c sub k. So it hasn't been received by the server. However, something is going on right here. So it's telling me at layer three, the source and destination IP addresses are written up in here. So as you can see, I have a 192, 168 dot 10 dot t2. And that is for the source and the destination is the dot one. And it is an ICMP message. And I also have at layer 2, the MAC address of the source and the MAC address or the destination. At layer one, which is the physical layer. You have which port it's coming out of. From. Now. This here again is the OSI model view. Can we look at inside the frame? And, or the PDU, or what we call the Protocol Data Unit, right? So let's look in there. And sure enough, notice it's broken down into Ethernet, which is layer two, IP, which is layer 3. And then the actual message at the bottom, which is the ICMP. So let's look at the top here. Notice here at layer two, we're at, as far as Ethernet protocol is concerned. For this frame, we are concerned with the MAC addresses. So this is the destination, and this one right here is the source. Okay? If you had to map it to a logical address, that would be through the IP. So this would be the source address and this would be the destination. Okay? And it's also saying, all right, So what kind of application or what is it we're running? It's an ICMP message, right? And so, good. Now, let's get that frame to move. So we're gonna go over here. So we're not going to click in the middle here. If you click in the middle, it's going to run the whole simulation at once. We're going to click on this one right here. So we can do it one step at a time. And notice the envelope reaches now the server, right? We haven't had a reply. It remember this is a step-by-step simulation by clicking on this button. And notice it's not completed, it's still in progress. Okay, so if we click on this envelope now, what do we see? We have an incoming message and the potential outgoing message from the server to the destination, this would be the reply. Now it hasn't reached the, the, the, the, the source yet that sent that ICMP message. Remember your envelope or your frame? It's still within server to right. So and again, this is at the OSI level, what layers are involved? Layer 321. And if you look at the BPD use or PDUs associated with the inbound or outbound are pretty much similar except for the source and destination. Okay? So for the outbound, the IP bound, so the inbound, notice the type for the ICMP that was the message being sent their outbound will be the echo back. So the type will be slightly different, right? Fantastic. So now let's step it one more. And notice now it's been received and notice a nice little checkmark. And at the bottom here it says successful. That's the end of it. Okay? So and again, that would be the message being sent. Let me do it from here. Actually. Here's the message, right? And it got received by the issuer of the ICMP message, that will be the ACO. And here's the information at this level. Okay? And that was the type received. Okay? All right, so now what happens if I click on Step again? Well, nothing, it's done, it's over. Okay, I hope you'll learn a lot and I'll see you for the next lesson. 6. Connect Multiple Devices: Okay, let's pick up where we left off last time we had two unknowns, we connect to them with the media. And we've set the IP address for both. And we were able to monitor and observe a frame that goes between these two end nodes with by using an ICMP message. Now, the limitation this network gives us is basically simple. Each one of these has one port. So it is a point-to-point connection. What if I needed more than one computer to access this web server? What can we do about it? Well, let's start a new fought for this. So let's close this simulation here. Let's go to real-time. Delete the scenario we had, save everything we already had. Alright, so I'm hitting Save. Now I'm going to create a new file. And I'm going to say yes. And now we have a new file. And we're going to recreate kind of the same scenario, but this time we want multiple PCs to be able to access the server. We're going to do this at layer one in terms of the inter-networking or the device that will allow the inter-networking. What we will use, in other words, is a hub for k, which is a multi-port repeater. Okay, So we could start with the hub right here. So as you can see here, where I'm going, here's the categories. You have routers, switches, hubs, okay. Then you have wireless devices. We're not doing any of that. We're just going to pick up a hub, a wired hub. Okay? And so I'm going to pick that hub and put it right here. Okay? Now if I wanted to look at physically what the hub looks like. Now notice by putting my mouse on it, as you can see, it has six ports, okay? And they're compatible to Ethernet. Now, if I double-click here, you can see it's a simple hub and the switches on. You can see that right here. So let me see if I can zoom in a little more ego. And it's got your six ports here. And you can update an upgrade, any other switches you want, I mean, any other interfaces you want right here, G got four slots in here. Okay? So this is a customizable Hub if you wanted to do that. Now remember, this hub is layer 1 device, okay? So it basically, if anything comes through one port, a gets transmitted on all other points. That term is called flooding. So let me repeat that again. It's flooding. So whenever an incoming message than all other ports will transmit out, that means everybody connected also on any of these ports are not only in the same broadcast domain, but they're on the same collision domain. So remember that take notes, all devices connected here will be on the same collision domain, as well as belonging to the same broadcast domain. Okay? All right, so let's go ahead and put a router. I'm sorry. Let's go ahead and put a server and a bunch of computers. So I'm going to pick a server. I'm going to put it right here. And I'm going to pick a few PCs. Going to put one here, one here, and one here. So I've got three PCs that want to access the server. Remember the challenge we had prior to this? The server only had one port and a PC only has one port interface, Ethernet port. So with the hub, we are going to basically have a star configuration. Visually speaking, in reality, any connecting to a hub where in a, in a, in a bus configuration, they're all sharing the same medium. Which means if any of these PCs or the server is broadcasting out or transmitting, all others cannot transmit out on the media. Otherwise, you're going to end up with a collision. Now the hub does not manage collision. Okay, So, so what's going to happen? Well, all PCs in all servers are going to be listening to the media once we connect everything. And if they see a carrier, which basically is the way you carry a transmission or information. So Carrier is basically a signal that you modulate over it, the actual transmission that you want. Okay? And so what's going to happen is if there is a carrier on the media, that means somebody's transmitting. And in that case, you don't as a unit, as an MD unit, as a, as an EndNote, you don't want to transmit. So you're always promiscuously listening to the media. For carriers, should you want to transmit and you see that no one is transmitting. Go ahead and put your frame out. Now remember where we're at frame level here, within the same collision domain here. Okay? All right, well, let's connect these guys. And let's go to the connection now, you could use the thunderbolt here. As you can see, if I do a thunder, I'm sorry, here. Let me select the fundable and go from here to here. Notice it's not even telling me which port to port. A better law automatically connect for you. If you want to connect yourself manually, notice with the thunderbolt that was in here, it gave you a straight through cable. This, as you can see, that's a straight through. So it automatically picked for you the appropriate cable. Either be a Cat 6, get five, whatever it is with RJ 45 on either end. Okay? But the configuration is a straight through versus a crossover. Remember in the previous lab, we used crossover when we connected a PC to a server. That's because they were like devices, a hub and a PC or not. Like a hub is a layer 1 device, EPC is a layer three device. So remember that. So that's why you're able to use a straight through. Now if you want to manually uses straight through, you can go ahead from Fast Ethernet 0. Notice here I'm going to have fat Fast Ethernet 0 for the hub is already taken when you use that thunderbolt. So you have fast Ethernet 01. Let's do it again. So if I go from here to here, Fast Ethernet 0 for this BC, notice what's available to me, right? So every time you use, you could use any of these. So I'm going to go fast Ethernet 2. Well, let's do the same thing with the server. Now, the server again is a layer three device. And now, and I'm going to click here, and I'm going to pick five so you don't have to go sequentially, right? Alright, so that's the amount of flexibility have here in terms of which port to use. And again, remember, if the server is transmitting anything, it will be flood. It will flood the hub. So that means all other ports are then, then the receiving part. Wool transmit that frame. Which means that frame will be replicated and transmitted on an alum would get to see this ourself, okay, in this simulation when we're, when we transmit the frames between endnotes. So when you do something very important here, all of these need to belong to the same domain, collision and broadcast. Okay? Now they are automatically the same collision domain. The fact that they're connected physically together through a hub. Next, how do you make sure that they're in the same broadcast domain? What are you going to have to set some IP address, layer 3. Okay? And what's going to happen is you're going to be mapping layer 3 addresses to physical addresses. And each computer, each server, we'll have what we call an ARP table. We can verify that later on that maps or basically matches a Mac to an IP. Okay, so that's something we can investigate layer one and look at the ARP tables for the end nodes. But right now the objective is to make sure that all of these can communicate to the server. And we're going to make this server a web server. That means any of these pieces will be able to pull that Webpage being hosted by the server. So for this lesson, we're going to do that. The upcoming lesson, we're going to go ahead and watch the frames, how they move. As we, you know, we, we, we, we either do an ICMP or a web page request, whatever service we want. Okay? All right, so for now remember, I need all of these to be in the same domain. Notice there are no IP address is set for these. All right, so I can go to this PC here. Let's start with the server. Let me go over here and go to config Fast Ethernet 0. And this is where you can say, okay, what will be the network address plus the host address? I like the private address, 192, 168 dot 10. And I'm going to call this one dot one. Okay? So. Always use the lowest values within your group, either to for a port for our router. If you have a router, that will be your default gateway by the way. And the next two it will be for the surface, that's your choice. As long as throughout your network, all your IP addresses are unique, okay? Otherwise you're going to have a clash. Let's go to the PC here. Again, same thing configuration and go to Fast Ethernet 0. And under IPV. For 192, 168 dot 10. Again, we will have a lesson on IP addresses, IPV4, and another lesson on IPV6. So bear with me right now, just replicate what I'm doing now let's suppose I made a mistake and I type one. And notice what I get. I get this address is already used in the network. Okay, That's really good. Now in real-world, you're not gonna get that message until it's too late when you're trying to connect. So the simulator is really working with you. So be careful in, in a real lab. Jot down, have a piece of paper with a map of all your IP addresses for all devices. Highly recommended you do that. Okay, so 192, 168 dot 10 dot two for this one. Let's do a DOT 3 for this one. Let's go to config. By the way, you could do this right here. So if you go to desktop and you can go to IP config right here, you can do it right here. 192, 168, that 10 dot a3. So there are plenty of places where you can actually do this right there. Now, again, we will be covering default gateways in DNS servers when we get there. Okay, So right now, really we're keeping the example as simple as possible, okay? And we just need to set up the IP address for our n nodes. And again, you could do it from the desktop, go to IP configuration, or you can go to config and go to Fast Ethernet and do it right here. And that would be 192, 168 dot 10, dot four, right? So if you click here anywhere in this space, the subnet mask is automatically assigned as a class C subnet mask. That's the default subnet, class C, Class C subnet mask. Are we going to use non-default subnet masks in the future? Absolutely. Right? So it depends on our strategy. Right now this gives us basically 256 combination. However, two addresses will be taken out. One will be for the broadcast and one will be for the network itself. So you cannot use 192, 168 dot 10 dot 0 to identify a device. And you cannot use the last address that within that block as 192, 168 dot 10 dot 255. For a device, dot 0 is to identify this network. Dot 255 is reserved for broadcast. Okay? So the last valid, and let's do it. The last valid one will be 254. Okay? Can not use 255. Now watch what happens if I try and do 255, I get invalid subnet mask. Okay? Now 192, 168 dot 10 dot 0. Now let's suppose I did that. I get invalid subnet mask. Okay, those are the two extremes you can't use. And well, let's say I didn't know anything about IP and I did something like this. 168 dot 10, dot 200. Okay. Well, that's fine. Let's 300. That's beyond range and you get an invalid, right? Because your max value is 255, right? To a 100 is fine. And nobody else has 200. Remember the max address 254 for a physical address, I mean logical address for a physical and melt. So 192, 168 dot 10 dot 254. So let's pick the last one there, right there. Good. No news is good news. So we're good there. All right, so now let's pay attention here. Let me just hover my mouse here. Notice I have an IP address. Notice I have an IP address for that one. I have an IP address for this one which is 254, right? And this one should be three. As a host. Good. I can ping between them. I can go to this PC here. Let's go to the desktop. Let's ping the last one, 192, 168 dot 10 dot 254. Okay, and there you have it. Now, here's another thing. Remember I mentioned an ARP table. Okay? So what you could do is you can actually look at the ARP table for this computer, in particular, ARP minus a. So this will be the command for it. And notice it recognizes that there is a computer on this network called 254. And remember where I am. I'm right here. Ip config shows you where you are. Okay? I am dot t2. But when I do ARP minus a, I can see that I have access to 254. And you know what? It knows that because when I sent that ICMP message, 254 responded back. Okay. And the fact that it responded back, I know that it exists on this network or at least within my own collision domain. And if that's the case, I can actually put it in my ARP table. An RP stands for address resolution protocol, right? So what it allows me to do is assign an IP address to a MAC address. Now that's important because if I get a frame, and we've seen that in the previous lesson, in that frame there will be a MAC address that says, hey, you know, I'm the one who said this. Ah, then I know logically what IP address belongs to that. Okay, Well, that leaves the gate open for men in the middle attacks. That's a non-atopic. Okay? All right, so now that we've seen that this can ping that one, now let's say if the pings the server, okay, so let's go ahead and ping the server, 192, 168 dot 10 dot one. And to prove the point, Let's go ahead and do an ARP minus a and C If an updated its ARP table. Now, in real-world, this is done automatically. Here, it's done manually every time you ping. You're also updating your ARP table. So let's do an ARP minus a. Notice now I have two addresses in my ARP table. Okay, so that's one quick lesson was far as RPS concerns. So the more I get responses within the same collision domain from other devices, my ARP table gets populated. Can I edit what's in the ARP table? Yes. Can I delete an entry? Absolutely. That's another lab. All right. Okay. So now I want to make sure that I can access the service, this this servers for studio. Well, let's make sure that we have that service. So let's go to services. And we're gonna go to http right here. And you can see it's on, sorry, it's already turned on. And it has an index.html page that it hosts plus other pages. Let's look at it again. You don't want. Let's add something in there. In, in, in the page. Now this is the default page they put in the simulator. And I'm going to type hi there. Welcome to Drew Prof, crazy class. And I'm going to add it in there, save it. There is already a file with the same name overwrite and I'm going to say yes, okay, let's see if it appears. So what I'm going to do is go on PC. You can do this anywhere and go to desktop. So let me just close this and go to the web browser, right? And let's go ahead and do a 192, 168 dot 10 dot one. Let's see if we get that. And sure enough, welcome to the Cisco Packet Tracer. And again, anything that I edited down that page. Hi there, Welcome to Drew Prof, crazy class. Okay, let me put a comma there. So I'm going to go back and edit my webpage. And where it says, hi there, let me put a comma. And this is within the body of the HTML page. And I'm going to say yes. And let's see if other computers within the network access the same web page. And we're gonna go here. Remember I'm on another computer and I'm going to point to the server. Notice the server does not have a name like www dot my Right. So it hasn't been resolved. We didn't set up anything for that, so you're going to have to access it using an IP address. So 192, 168 dot 10, dot one, right? So and notice server reset connection, okay, oh, D2, I taught the wrong one, right. So D2, that's not a server. That one, That's good. It's good thing we made a mistake. Hit go, Hey girl. And notice the common now is showing up, right? And we can see that this is fun. You can go to your server and update the webpage you want to, you want to show, right? So you can do whatever you want in your lab as you replicate what we just did. Okay, I wanna make sure this computer here also can access it. And 192, 168 dot 10, dot one, dot two No.3. None of those are I'm hosting a web page, right. So this one, excuse me, this one does. Perfect. So I hope you'll learn a lot from this. And the next lesson we're going to look at the simulation. We're going to use reuse this file to look at how the frames move. We're gonna do some ICMP messages and then we're going to use the step-by-step simulator and look at the actual frames to observe what they're doing. Fantastic. See you for the next lesson. 7. Monitor Frames and Start of Project: Welcome back. For this exercise. This will be an exercise. We're going to monitor the frames as they are generated by the N nodes. And as they go through the hub, we will observe the flooding of the ports at the hub level. And then where continue without observation and see how the frame reaches its destination. What happens where the receiving end node, what it's supposed to be doing depending on the protocol you're using. I will start the example with an ICMP message and I will go step-by-step. Your exercise will be when you have to do an HTTP can basically running an HTTP application using TCP as your connections is going to be a connection oriented connection between you and the server or the PC and the server. In other words, you're going to have to describe the three-way handshake, right? And you're going to have to observe somewhere in there the acknowledgement and all the other messages associated with the three-way handshake and the actual payload management of the transfer of data from the server to the PC. So that would be your part. My part is show you a simple example with ICMP. You're going to repeat the same thing by connecting to the server, a web browser, and then at same time running the simulation. Okay, so let me do the scenario now with ICMP. And so what I'm gonna do, I am going to go to Simulation mode right here. Okay? And before I do anything, first of all, let me go to each computer here. Let me just close this for a second, just, just so we have a starting point. And you understand that each one of these computers right here have an IP address. So for example, this one, if we go to the, it's fast Ethernet has an IP address, is from the previous lab we did together, right? So this one has an IP address. So make sure that all your computers have an IP address. Watch the previous video when we did the hub lab, okay? Right now you could use your mouse to hover over the end nodes to see they all have IP addresses. They all belong to the same broadcast domain. And they are all physically connected to this hub with straight throughs, which means they're all under the same collision domain. So that's quick review what we've done before. Perfect, Now let's go to the simulation. And here we are. I'm going to go to this PC right here. And I'm going to go to its. A command prompt. And let me clear the screen here. I'm not sure if CLS works here, where it's not taken up all the DOS commands here, but that's okay. Let's do this. Let's, let me close it and bring it back. So hopefully that will. No, it doesn't. So it's always, it has all the instructions we've done before. So at this stage, Let's go ahead and do a ping to the server, right? So let me do an IP config for us to see who we are. Here we are, We are 192, 168 dot 10 dot t2, that this PC 0 right here. And it shows PCI right here. Now we're going to do ping 192, 168 dot 10 dot line. Okay, so I'm going to hit Enter. And notice that my command requires that we access the network and transmit a frame across. So let me just move this to the side here. And notice that there's a frame right here sitting at Idol with PC 0. If you look at the simulation, That's exactly what we have right here. It's an ICMP message and a sitting here. So if I click here, you can see from an OSI point of view, this is an outgoing frame with point to as the source, 0.1 is the destination. At layer three. At layer 2, the MAC address or the MAC layer, you have the MAC addresses of the source and destination. And then at layer one, which is the physical address, the port, it's going out front. And then here is the frame. This is an Ethernet frame. If I scroll down, this is an ICMP message, OK. And it's going to require that receiver. Basically the server will send an echo back. Okay? So we could do this one step at a time. So let me just close this here. But I want you to see now what happens when it goes to the hub. Right? So it's at the hub now. Now, let me click one more time. Watch what the hub does. Bengal. What did the hub do? What did I tell you about hubs? Basically that will flood all the ports. Write a message coming in from one port. They're going to come out on all points. So we're seeing that right now. Notice that these big Xs here that are flashing, that means these computer recognize that this frame doesn't belong to them. Let me just click in there. You can see they're not intending to reply at all. Okay? So they are basically they've received this frame. But they understand because the destination MAC address does not match their own, they don't have to respond. Okay, that's a key ingredient in this network. Now, notice that x means they don't have to respond. Let's go over here. This one. On the other hand, the, the, the, the outgoing message is being prepared right here, okay? At least from the OSI model point of view, we can see the outbound PDU here and the type 0, 0 it, which is an echo. Let's go to the inbound, which is time 0, 8, which is the request. Okay? So we can see there are two different messages. And this one here is preparing its echo back, right? To acknowledge that. Yes, I did receive it and it's ready to be transmitted. So let's see what happens now. So if I go to the next level, boom, it gets transmitted. Now remember your hub does not remember or even acknowledge that the other PCs don't need those frame. Now, if that was a switch, that would have been a different game, that's another lap. Okay. So because it is a hub, it doesn't care what it's gonna do now it's going to flood again. All ports. And again PC1 and PC2 will not respond because, hey, you know, the destination MAC address doesn't match theirs. So they don't have to do anything. However, PC 0, on the other hand, says yep, that's for me, transmission complete. And that's it. I mean, if I keep clicking here, nothing happens. I'm just repeating the same process. You see that? So I'm just repeating the same constant. Okay, So now let me clear up this one and let's do it again in a different way. And let's go real time. Let me go to simulation. And we're going to repeat that command right here. Ping 192 dot 168 dot 10, dot one. But this time I'm going to simply run it. I'm going to hit the Run button right here instead of step-by-step. Watch what happens now. So it gives you an idea. So it pauses for a second or two. Boom. Floods all ports. Server's gonna respond back. Floods all ports. Hey, go. Pc receives a check mark, we're good. Okay, so what happens with PCs? When that happens? That means right here. Notice here it's sending, that's the first element. So notice it's doing it again and again. So we have all these packets here begins being said right here. Watch this. This is happening live. And let me just move this to the side here. So remember this, this one line by line until it's done. So. All of these heavy to be transmitted, that will be received. The server will echo back. Okay? And we can see the time it takes. Now obviously the simulator slows down the time. There's no way you can catch four milliseconds, visually speaking. Okay? But the simulator is slowing it down for us. But it's the effect of four milliseconds per transaction. And you go okay. Responds back. Frame will be received. And that's the last one. Okay? So $0.04 for received 0% loss. Okay? All right, let's do that for connecting to the website and see what the story is behind. Now this is your turn. Okay, So let me reset this. I'm just going to close it and turn it back on. Go real time. Go back here. Okay. And I'm going to go to the PC now. Any of the pieces, let me just go over here. Pc1 this time. And I'm going to do an HTTP connection. I'm going to go to 192, 168. This is what you need to do in your write-up. What you need to pursue, dot 10, dot one. Now as soon as I hit Enter, notice the simulator is freezing everything, which is fine. So you can run it and you should run it one step at a time. So what I'm gonna do, however, is run it completely and watch the frames going back and forth. And what kind of frames. Prior to this, when we did the ICMP, there were all ICMP frames. The type was slightly different. Okay. So you had Type 0, 0, 8, or type 000, 000, right? So here, let's see what happens. I'm going to run this whole thing. And at same time I want to be able to see what's going on with the webpage. Notice we're establishing a connection. K Notice the other pieces do not need to reply, but the hub will always transmit on all ports. Notice what PC1 is doing. Once it has completed a TCP connection, then we have an HTTP application running. Okay? So I want you to go step-by-step however, and try to understand what happened. Now notice at the end, what trend up with is the webpage loaded up on the browser. The connection has to close. Okay? So you have to establish a connection and then you have to close it and I need you to observe that and see how did that happen. Okay, so notice it's still Dorian even though it loaded the page. Okay. Now what can we loading a page is high faster than this. But since this is a simulation, it's slowing down every step. Okay, done. Okay, so now we've captured all of these transmissions. You need to figure out what are they for. Have fun, and I will see you for the next lesson. 8. More Simulation to Support the Project: Okay, a couple observation I want to add while you're doing the exercise from the previous lesson. Let's assume, let's go to a computer here. And what I'm gonna do is clear the cache and see what happens when you do an ICMP message. So what do we mean by clearing the cache? Clear the ARP table. Well, first let me do an ARP minus a. Let's see what's in there. And let's say we ping some computer. Ping 192, 168 dot 10, dot one, or right here. Okay. Let's go real time and do that. Obviously the simulation is working now, hey, GAAP profits. So now if I do an ARP minus a, as you can see, my ARP table has two entries in it. Okay? Now, if I try to reach the, the server, knowing full well that it's already in my ARP table. Let's see what happens. Okay, so this time I'm going to use the simulation. I'm going to go to the computer here and close this and run this and try to reach 192, 168 dot 10 dot one. Okay? And notice right away It's a TCP frame to frame that is associated with the TCP application for connecting, right? Right. So let's see what happens here. So with TCP, by the way, you can see it's a layer four, right? Artifact for connecting. This is connection oriented. Okay, very good. So let's go ahead and run this. Watch what happens. So it's running. Now we know that we have the server in the ARP table. Okay? What I'm gonna do next is remove or clear up to our table and redo the same scenario and observe what happens. So I want you to add that to your exercise in terms of some of the, some of the observations. Because there could be two cases where you already have knowledge of the server within your ARP table. And then what happens if you don't? Okay, so notice now everything we're getting the type. It's either TCP or HTTP, predictable. Not a prop. That was what we saw in the previous video. Okay, let me reset it for a second because this will keep going. But this time I'm gonna go back here and let me just close this and go to run. And I'm going to clear the ARP table. Again. If you do an ARP minus a, you can see what's in our table now if I do an ARP minus d. Okay, and let me reset the simulation is it's telling me that that's what I did here. So even if I run that, so it's going to send a packet out. Okay? And notice this is a frame, and notice it's doing ARP. By the way. If I pause it and just pick one of them, this is what's going on. This one does not have to answer because it's not intended for it. This one also does not have to answer. This one. My not answer at all. Okay. As you can see, let's see what happens next. And that's it. Okay, so let's clear that. Let's go back here. And let's do an ARP minus a. And there are no entries. Perfect. Now let's try to access the web server. And in particular the webpage, right? So I'm gonna go back here, close on this, do this. And I'm going to type 192, 168 dot 10 dot one. Now watch what happens. Okay, Let's run this. As you can see, not only you're doing a TCP, but you're going to have to do an RP to populate the ARP table. Okay, so the same idea, the same objective, but two different scenarios. One, you ARP table already had some data or to your ARP table was clear and had nothing in there. This is the scenario where you had nothing in the ARP table. So as you can see before even establishing the full connection, we had a whole bunch of frames with AARP enum. And then once this is done, let's go ahead and verify our computer PC 0 if its ARP table has been updated. All right. I can go to real-time that will accelerate things. Okay. And let's go to the computer here. You can see the webpage loaded out. And what I'm gonna do now is go back to the command prompt and run ARP minus a. And I want to see if indeed I have ensure enough, I have information on 192, 168 dot 10, dot one. Okay. And that was done while I was trying to access a webpage on the server. All right. So it does not have to be a pink. So when you're using either packet tracer or in a real-world, you're using Wireshark and you're seeing all sorts of frames that has RPT ice while you're doing an ICMP or an HTTP. Understand that what the computers are trying to do is build their ARP tables as well. While the service connection is being established. Keep that in mind. Go back to the previous lab and completed now that some of these had been clarified for you. See you then.