 Hi there. My name is Ken Mayer, and I'm going to be your instructor for this course. Over the last 30 plus years, I have worked in a variety of different fields in the world of IT. Of course, that does include the routing, the switching, and the security world, both for small enterprises, large enterprises, Fortune 100 companies, and over the last 15 years, I've had the opportunity as a consultant or as a contractor to be able to work with most of the larger service providers around the world. Now I'm hoping that I'll be able to take all of that experience, both in the real world and in the instructional capability, and be able to give you the information you need to be successful at working with Cisco's routers and switches. So let's first talk about exploring the functions of networking. That means, of course, to understand the basics about our communications. When we talk about a network, what we're talking about is a way for different endpoints to be able to communicate with each other. When I talk about an endpoint, I'm talking about a device, like a laptop, like a computer sitting on your desk, that is not going to take and receive transmissions and then send those transmissions out to a different device. It's the beginning of a conversation or it's the end of a conversation. We call that the endpoint. Now that endpoint can be anywhere. It could be at a home office, a small office. It could be a user who's mobile. In today's world, it could be part of what we call BYOD. Bring your own device, your smartphones, your tablets. All are designed as endpoints. Now what we need is to find a way to be able to help facilitate that communications from one endpoint to another, whether it's at a branch office, a headquarter or main office. And so that's what we call a network. A network is the ability for these endpoints to be able to talk to each other. By the way, some of the other endpoints that I haven't mentioned are obviously things like your servers, your file servers, your print servers, your email servers. We just call them a server because they are designed to share resources for multiple endpoints or I guess what I'll just call workstations. So what we're going to do is find a way to be able to make that communications go back and forth, whether it's from the use of radio frequencies like a wireless network, whether it's the use of copper cables sending electrons or fiber cables sending photons or light down that wire. We're going to look at the ways in which we can make that connection to help facilitate the communications to get the message from the source to its destination. So in reality, as I said before, we're looking at the variety of endpoints that we want to have communications work with. And endpoints don't mean again that it's the end of the communication. It means they could start or end the communication, but that they're not helping facilitate the communications between each other. In other words, if my computer wanted to have this user send a print document, they would send it through a network device that would look at the address that it wants to be communicated with and then help facilitate that communication to the device so that the print job could work. So that's where we're looking at the interconnection right here from the switch layer on up. And we'll break this down a little bit to talk about these different layers, but typically we talk about this as the access layer. Because at the access layer, what we're doing is we're making sure that we are able to access the endpoints. And then of course, the larger our network grows, the more that we need to have the ability to do what we call scaling of communications. We may start using routers. Now I'll explain all about the reason why you would use a router over a switch as we get into the discussion of broadcast domains and so many other things. But we often call that the distribution layer. And we again use it to help facilitate the communications from one place to another. A router could help us within a local office. A router can help us in being able to get out to the world of the internet as well. So as long as these symbols make sense to you and we'll keep showing these as parts of our diagrams, then I think you'll do okay at being able to understand or hopefully interpret the information that I'm trying to share with you. Again, as we're trying to interpret these diagrams, it's important to remember that whenever you see a PC, a server, or some other endpoint, that it's generally going to have an Ethernet connection. Remember the straight lines were Ethernet cables connecting to a network device. Most often we're connecting to a switch at the local level. Again, the switch with the square with the arrows moving out. And as we're looking at these diagrams, you're seeing the port numbers and the type of ports that they are that the devices are connecting to. For example, FA generally stands for fast Ethernet. And when we get into the speeds of Ethernet, you'll see that that's generally speed that we always measure in megabits or actually in bits per second, but generally megabits per second. And fast Ethernet is designed to be 100 megabits per second. So this is port 05, port 07, port 011. Now we have another indicator here for a different type of interface, which is what we would call a gigabit. Gigabit is, again, a factor of 10 times faster than fast Ethernet. And so gigabit would generally be listed as 1 gigabit per second. Again, we're talking about the types of interfaces that we're connecting to, and that's what it's showing us in the diagram. Now, when we look at moving through layer 3, we haven't got to the OSI model yet, but layer 3 deals with IP addresses. So far, everything over here can deal with a layer 2 address that we call a MAC address. And I promise we're going to get more discussions about that. But at layer 3, we do need an IP address. So generally speaking, you're going to see the network address. The network address will generally end with a 0, but we have to still talk about the subnet mask or variable length subnet masking soon. And then specifically, we have the host address. That dot 1 means that it would actually replace that 0. And that would be the specific address of that port that is connecting on the switch, a dot 2, to replace that 0 for the address on the router. And again, that is a gigabit connection. And the ports, again, are designed to just show you which port numbers they are. Basically, the port number is the last indicator. The first indicator generally is for a multi-chassis or multi-designed chassis having multiple switches in one box. And we'll talk more about that. In other words, if I had a very large switch, I may have several of these line cards. And each line card could have multiple ports. And so the first number is telling me which line card, starting with 1 or 0, going to 1, 2, and 3. And that would be that first 0 that you're seeing here. And then on that line card, which port number we're talking about, starting with port 0, port 1, et cetera. And then some communications that we may use some other medium besides Ethernet. And so this is an example of a serial interface. Serial is still about communicating traffic. It's just using a different protocol and a different type of cable for a variety of different reasons to be able to make the communications. Now, when we're designing a network, you really want to make sure that you understand how user applications can affect your designs. For example, we have a group of things we may call a batch application. Batch applications are generally applications that might require a lot of bandwidth. Bandwidth or speed is about how much information I can send down a cable at any one time. And even though they require a lot of bandwidth, they don't necessarily worry about how long it takes for the data to transfer as long as the data does transfer. In other words, I could start some of these applications like a file transfer, FTP, the file transfer protocol, or TFTP, the trivial file transfer protocol, or maybe it's a database doing an inventory update, but I'm sending a large amount of information. And it may be okay if some of that transfer is interrupted by other traffic coming through because it's not important that it gets there in a continuously same-speed type of fashion. Now, these generally have no direct human interaction. We start the programs, they start sending out their information, and then they finish and report to us when they're done. Now, there may be some interactive applications where the time it takes to get that information could be important. It could be somebody hitting a web page trying to get information from our database about what items we have in inventory. So in that case, we have that human-to-machine interaction. Somebody clicked on that request. We're expecting to see the results come back. And we don't want to wait a lot of time to be able to do that, where we actually worry about how long it takes for the people waiting for the response. And response time, although important, not quite so critical that it can't have a couple of delays in there. Real-time applications like voiceover IP or video streaming, we do care about because if we're making a phone call over our network and we have a lot of delay, it'll suddenly sound like we're on a CB radio instead of actually on a phone. Or if there's a problem with the transfer video and we're starting to see delays and skips, making the video experience very bad, or having a problem with the video and the voice coming together at the right time, making your video look like a badly dubbed movie, then that can cause a lot of problems. That is usually a human-to-human interaction doing voice or video phone calls. And so it's very important that we don't have any delays. And so all of these are considerations you have to come through when making the design of your network. So we're going to talk about the characteristics of a network. The next couple of our slides are going to talk about the logical and physical topology. But basically, the topology is how do we connect one PC to another PC or to a printer or something else. And that means there has to be some sort of a wire, some sort of a device that can help make what we call a forwarding decision because there may be more than one destination and we need to make sure we get our traffic to the right destination. So then we'll look at that topology information in just a little bit. This, by the way, is my drawing of a switch. I just didn't put all the extra arrows. I guess I could have there for you. There we go. So one of the things we do look at a network is speed. Speed is sometimes called bandwidth. It's about how much data can I send over this physical cable. There's also the use of cost. Cost is also important because we'll talk about a variety of speeds, but the faster you want the speed of not only the traffic going over the cable, but the speed on which the device that you use, a switcher router, can help you in forwarding traffic can also become more expensive, generally speaking. We also look at the cost of how many devices can we connect with this switcher router. Security is always going to be an issue. Security is about making sure there's not some hacker out here that might be a part of your network that's trying to make a connection and steal communications or break into other people's devices or even change the way in which your traffic moves across your network. So we are going to talk about some of those issues as well. Security not only for the people who are trying to happily use the network, but also security about the device itself that they're interconnecting through. Availability is our discussion of what we sometimes call the mean time between failure. So what's the odds of a cable breaking? What would that do to us? What if the entire switch or router failed? How would that affect communications? Do we have a plan for having alternate paths? Scalability is when we decide to increase the size of our network. Scalability would be the discussion of should I add another switch so I can add a few more endpoint devices into my network. And what would that do to the bandwidth utilization or the amount of traffic that exists on there? As well as reliability, reliability still comes back to kind of like availability, letting us get a good understanding of can we suffer a single point of failure? In other words, if one cable went down again, would we have as good of a network? The other part of reliability is what happens when I start introducing voice over IP, somebody having a telephone, which by the way I draw my telephones like the old dial telephones with a headset on the top. And how would that affect my communications? In my network if I don't have either the availability or the reliability of being able to avoid congestion. One of our earliest topologies was what we call the bus topology. Each of these little spots actually represent an endpoint, basically a computer, laptop or something like that. And what a bus topology was known for was that if any message was sent by a computer, it was just a physical cable. Kind of like if you've ever plugged a power strip into a wall. Instead of having one electrical outlet, then you have six electrical outlets. Everybody gets to share that energy being sent through. And so a bus would basically send your message out to everyone. So everybody got to hear it. If you go back long enough in time, we often call that a party line. Or if you have more than one actual landline in your house, if you actually have phones that are landlines not cellular, then that was generally a bus topology as well. Everybody got to hear your conversations. So think of it as a bus line then, right? We came in there, it was like a bus route, you hit all of the stops. The star topology was a way of connecting multiple devices. And I'm not quite so sure I like this little circle being in the middle because generally we had it like a switch, even a hub in the older days that were in the center of this. But all the devices would connect to ports in this switch. And so it kind of gave you the impression that everything radiated out from the central part, kind of where the star topology came from. Depending on the actual device, if it was a switch, and we'll talk about these differences, if a communication went in, that device would only send it out to the recipient and not repeat that information for everybody that's on there. A mesh topology is where I am not connected to any one central device. But whether we have basically, let's say maybe a switch or a router, that has more than one connection to be able to send traffic so that if any one interface goes down, then I still have another way of being able to send my traffic. Now the internet is a great example of a mesh topology. All of the service providers talk to each other. The service providers have their customers, you and I, and they facilitate the ability for you and I to talk to customers in their network or to send our traffic to another service provider so we can talk to their customers. And so when we look at service providers, we often think of them as little clouds. And so, again, we have all of these little clouds talking to each other. Now I'm not going to try to promote any one service provider, but you know who you use for your own internet at home. They are a service provider. And the idea of the mesh is that we make sure there's not just one way to get from where we are to where we want to go. It gives us a little bit of fault tolerance. So those are the three primary. There is another one that often is talked about, it's called a hybrid. A hybrid is sometimes a combination of connecting maybe a bus to a star. So you have both types of topologies set up for you. One of the most important parts about topologies is what I just talked about was a physical topology, how the actual cables were laid out. A logical topology talks about the paths that signals use to travel from one point of a network to another. And so I want to kind of talk a little bit about that and go back in a bit of time. For example, a switch is designed to be a star topology, physically and logically. But before we used switches, we used a device called a hub. And for many of you who are new to this industry, a hub and a switch might look very similar to you in that it's a single box with multiple ports. And our goal was to connect our PCs to each of these ports. Now, physically, this hub would look like a star, right? It all radiates out from a center device. But actually inside, the way in which they were electrically connected was a hub. So that if any transmission went into the switch or hub, excuse me, let me put hub here just so I keep remembering, it would exit every single port in that device. So logically, it operated like a bus. Physically, it looked like a star. So what we are interested in is both the physical layout, physical topology, and the logical how the paths are used for the signals that are being sent in and how they're forwarded and how they travel basically from one point of the network to another. Well, the goal of this lesson was to talk about how a network is basically a connection of different devices that are designed to communicate with each other, what we call endpoints. There are four major categories of the physical components in a computer network. Those were the endpoints that I called the computers, the way in which they were interconnected with the physical cables, the switches and the routers. Now, of course, we can get into detail about any of the ways in which switches and routers work specifically, but we're just looking at the diagrams. We talked about the icons that are going to be used to represent these different components of the network. We also talked about some of the types of applications that we want to be able to plan for, whether they are batch applications interactive or real-time, like voice over IP or video. We looked at the way in which we describe networks both physically and logically, as far as the way in which they are designed. That's what we call the topology. Now, within that, of course, we also needed to talk about some of the other ideas between speed, cost, security, availability, scalability, and reliability. Now, remember, physical topology is the way in which the wiring is laid out. A logical topology was about the path that the traffic took.