Networking Review

We covered a ton of information in this module, and some of it is more important than others.

The terms

Here's all the videos and terms that we covered throughout this module. In the ideal world, you would be able to know what each one of these are and be able to tell me what the concept is behind each one of these. Unfortunately, we don't always learn that way. Some of us can, but others of us need to go over it many times, and I want to make sure that you're focused on what is the most important. So I starred the ones that are the most important here. We're going to cover some of these when we talk about the concepts, while others of them I'm just going to do a brief review right now.

For instance, a protocol is just a set of rules that set up communication between two devices. A port is so that way we know which service a communication is connecting to — so that when a packet comes into a device, it can process that and know which service to send that information off to. A network interface card is the interface between our computer and the network. A MAC address helps to identify or send traffic to — it's an address on the local network that we can send traffic to, and we would send it in the form of a frame. A local area network is what all those end devices are communicating on. An IP address is something that we can use to communicate — that's a hierarchy address that we can communicate on a more global scale. A packet is what we send that has information on it such as the IP address. And then a WAN is a wide area network.

Local and wide area networks

A local area network consists of our different clients on this network, and this defines our local area network. So this is the boundaries of our local area networks, and it's serviced and connected by something like a hub or a switch. In this diagram right here we have two local area networks, one on this side and one on the other side. And connecting our local area networks, because there's some distance in between these, we call this a wide area network, because perhaps this is cities away or maybe it's even countries away. So now we need a wide area connection between these, and then these are our WAN links between these two LANs, between these different geographical locations.

Our MAC addresses is that 48 bits that are burned into our machines, and we use that so we can communicate across the LAN. If this device wants to talk to this device over here, it will use its MAC address and send the frame out to this destination MAC address so it can be delivered to this computer.

We also use these IP addresses, and the IP addresses are used so we can route things on a more global scale, but we use them internally too. It can be used on the LAN. It's just not for that initial delivery onto here. But we do still have to have an IP address assigned to the machine for that local delivery.

How a packet travels

On a more broader scale, if this machine wanted to talk to this machine, what it would do is it would form the data. Maybe this is a web server right here, and so it would form a request for those web pages. So what it will do is it will form that request right here, and then it will put what we call a layer 3 or an IP header on there that has information about the IP address of this machine over there.

And then so it can deliver it on this local area network, what it'll actually do is it'll send this to this interface right here. So it'll put the MAC address of this LAN, the destination on the LAN right there, and it'll put that as part of the layer 2 header here. And then also has a little check at the end here. So it will form this frame. This is the packet right here, and this whole thing then is the frame.

It will send it out on this network and deliver it to this router. The router will receive it and take a look at that layer 2 and say, yes, that is part of my MAC address, so I'm going to process it. Although I don't need my layer 2 stuff anymore. What I can do is then take this packet and I'm going to forward it on to the next router. So now I need layer 2 information that's going to address the next router. And so then it will form this frame and send it along its way to get to this router right here.

And then that router will take a look at the layer 2 and say, is this for me? And if it has the MAC address — or whatever kind of addressing it is, because this might not be Ethernet and it might not use MAC addresses — whatever it's using, it's going to take a look at that address and see if it's for this machine right here. If it is destined for this machine, this router right here, then it will drop the layer 2 information, and it'll take this packet and say, where does it need to go next? Determine that it's this router over here, and then it will form an address to be delivered on this connection right here and send it along its way.

This router will go through the same process, take a look at that layer 2, and if it's destined for this machine right here, then it no longer needs the layer 2 information. It will figure out what is the next spot that this packet needs to be sent to, figure out that it needs to go to this machine next, and then add the MAC address of that machine. And so it'll add the layer 2 information and send it on to the network to be delivered to this machine right here.

And so now this machine will receive it. It will take a look at the layer 2, make sure it's destined for this machine, remove that, and then take a look at the layer 3 and then do away with that. Take the data and deliver it to its web services.

So those packets for the most part remain the same throughout this whole process, and the packet is going to look the same. The layer 2 part of this, though, is going to look very different on each step along the way, or something we call actually a hop along the way. So it's going to look a little different as it goes through this process and goes through different types of technology.