Layer 3 (Network Layer) – CompTIA Network+ Tutorial
Layer 3 (Network Layer) is a free tutorial by Jason Dion � 200,000+ Students Worldwide from CompTIA Network+ course
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Course summary:
Passing the Network+ certification exam with confidence
Understanding computer networks, their functions, and their components
Subnetting networks
Performing basic network configurations
Becoming an effective networking technician in a small-to-medium sized business environment
English
-: Now that we’re at the network layer, we’re concerned with routing. Layer 3 is all about how we’re going to forward traffic, which we refer to as routing, using logical addresses. For example, your computer has an IP address. And that IP address is either going to be an IP version four or an IP version six address, or both. Now, both of these are considered layer 3 protocols. And we’re going to talk more about them as we go through this course. Now, the other thing we’re going to be concerned with here is logical addressing. I mentioned that IPv4 and IPv6 are two types of logical addresses, but they’re not the only logical addressing schemes that are out there. They’re just the most common and most popular these days. Now, we’re also going to be concerned with what’s known as switching. And here when we talk about switching, we’re actually talking about layer 3 switching, which is called routing. Now, I know this gets confusing because you’re using the term switching to refer to the function of routing, and when we talk about switches, the devices being layer 2 devices. So you have to keep this straight in your head. Switches, the physical device, are layer 2. Switching is another term for routing, which is how we transfer things at the network layer, layer 3. Now, as we talk about all these, another thing that comes up is how we’re going to do route discovery and selection. Now, basically, that means how do I know which way I want the traffic to go? We’re going to talk a little bit more about that, too, as we go through this lesson because we’re going to talk about connection services and bandwidth utilization and multiplexing strategies. All of these is at the layer 3 of the network layer. So to start diving in deeper into these concepts, let’s start out with logical addresses. There are lots of different routed protocols that have been used over the years. Back in the ’80s and ’90s, there was AppleTalk for Apple computers. And if you used a Windows or a Novell Network computer, you might have used IPX, which was the Internetwork Packet Exchange. Now, neither of these two are important for the Network+ Certification, but it is something that I want to bring up because you may hear these terms. Really, what happened was these were both killed off by Internet Protocol, which is known as IP. This became the common protocol that everyone uses on all networks and therefore, we didn’t need AppleTalk and we didn’t need IPX anymore. But the point is, at layer 3, it’s not just IP. There are other protocols that you could use in layer 3. IP is just the most common. Now, some of those are still existing on some legacy systems, which means old systems in some corporate network. But the routing protocol of the Internet that we use and the Internet you have at home and the network you have at home is going to be known as IP. IP comes in two variants, as I said before, IPv4 and IPv6. Now, if you look on the screen here, there’s an example of an IP address. It’s written as 172 .16 .254 .1. Now, we’re going to look at more IP addresses in a separate lesson as we dig deeper into routing later on. For the time being, I want you to think of an IP address anytime you see a number that looks like this. There’s going to be four sets of numbers, separated by dots. This is called a dotted-octet notation, and this is what an IPv4 address is going to look like. Now, how shall we actually forward or route the data across our networks? This is really the big question at layer 3. And there are three main ways for us to do this. You can use packet switching, circuit switching, or message switching. The most commonly used one in your network is going to be routing, which is also known as packet switching. This is where data is divided into packets and then each packet is forwarded on based on its IP address. Now, when I think of routing, I like to think about this as if I’m going to write a letter and send it to my mom. Let’s say I put that letter in an envelope, and on the outside of the envelope, I’m going to write the address of my mom on it. I put her city and her state and the zip code. Now, I put that in the mailbox, and the mail carrier is going to take it to a central location. Here, they’re
ipv4
