Hello, and welcome. My name is Tyler McMinn with Aruba, and continuing with our network essentials video course. Where you're going to be talking about the rest of our layers, layers three, four, and the upper application layers five through seven is how we speak about those. We're going to be covering that in this portion. Sit back, enjoy, and let's get started. Taking a look here this is layer three. Layer three is the routing layer. It's where IPV4, and IPV6 would sit. It's referred to as the network layer. The goal of this is to establish communication across multiple LANs or wireless, or excuse me, wide area networks. A LAN, as we discussed in the pop quiz, is a local area network. That is a way of referring to say, your house or a small business, or a portion of a large enterprise where you section off the broadcast, and the traffic requiring a router in order to go from one local area network to another. If I had a switch here with a bunch of devices plugged into it, here's the device right there. They want to go ahead, and route out. This would be their gateway, their route to the rest of the network. Between your switches those are individual segments, not the same as layer four segments. We just refer to them as point-to-point links. Then you've got yet another local area network here, where the router is the gateway for these sets of devices. Where we've got RPC, and maybe a few other devices that are plugged in to this switch right there. That is effectively your local area network. Your wide area network would typically branch off of one or more of these guys as it reaches out to the Internet or whatever your Internet Service Provider is. You can certainly have more than one route to it if you wanted to. But that connection through the service provider or perhaps your connections between these sites might be through service providers, If they're not at the same location. Those would be dedicated wide area networks as opposed to your public access to the rest of the world. Your Facebooks and your Googles, and your Twitters, and all that would be in the public internet space. Your wide area networks would be private connections that are hosted, and catered to you specifically by the service provider. They appear as if you're directly connected, like we are here at the same site, when in fact you might be thousands of kilometers apart. When you're establishing connections between your local area networks or a WAN, logical addressing is what we're going to do at layer three in order to know what our original source is, and what our final destination is. This is layer three addresses using Internet Protocol. The other role, and goal of layer three is figuring out the best path to reach that destination. This is typically determined by your metrics. Either use statically decide that you want to go this way, and forward your traffic or you could use a dynamic routing protocol rather than a static route to figure out which way this router is ultimately going to decide to forward a frame when received from a source, and is told I want go to this destination. The routers have to make their own decisions at each router as to which path is going to be the best. As new paths come up or the paths that you have go down, your router may end up switching what is considered the best path on the fly. In order to adjust to network changes that it runs across. That's the goal of layer three. Layer four the goal is to map your particular payload of data to a particular service or application that's listening for that traffic type. We use TCP or UDP port numbers here in order to allow that designation. If you look here, we take our traffic, we can segment it into smaller pieces, and then de-segment it on the other side. That means if you are downloading a rather large file, you'll typically chop it up into byte-size pieces. Specifically, we would refer to that as the MTU, or maximum transmission unit size, which by default has traditionally been 1500 bytes worth of information. A byte, in case you may not be aware, is equal to eight little ones or zeros or eight little bits of information. Each bit can either be a zero or a one. It's really how computers, and networking devices can understand each other at a more fundamental level. They're really fast at processing these ones, and zeros. If you're storing that information or transporting that information, you can refer to it as bytes of data. Your hard drive has so many gigabytes or terabytes of data. Your traffic is usually represented on the wire as bits of data where it's transmitted at so many kilobits or megabits or gigabits per second, that's in bits. But the actual data itself, we refer to as bytes of information. Anyway, just a little FYI there. All right, taking a look here, the last layers, five through seven, we don't really need to break those apart. We just refer to them honestly as the application layer. The goal of an application is to interact with a server running that same application like you on your browser going to Google, you're opening up Google's servers, and you're doing a GET HTTP request saying, "Hey, give me that web search results" or you open up a Facebook page, and saying, "Hey, get me my page on Facebook, I want to look at some stuff." The application itself is a standardized method of doing something online or doing something with a network. These network applications can have specific purposes like to render images on a page or to actually transfer files with the File Transport Protocol, FTP. What application you actually use, such as Chrome versus Internet Explorer vs Safari, doesn't really matter. They're all going to abide by the standards dictated by HTTP. Or if you want to transfer a file with FTP, there's a number of different file transport protocols that we can utilize. The function of layer five through seven, we want to identify your communication partner, and then provide the network resources to that user applications here. In this particular video, we did a short discussion on layer three versus layer four, the IP addressing source and destination at layer three versus the port numbers, source, and destination port numbers with the destination port matching what application you want to go to, the destination IP address, matching what device you ultimately want to pull that application or that information from or send to. Thank you very much for your time. In the next module, we'll take a look at an example of actually transferring information back, and forth in our own lab environment.
