Cisco CCNA 200-301 – WAN – Wide Area Networks

1. Introduction

Section, you’ll learn about wide area networks. I remember when I was first learning networking, that how Wan technologies worked in the real world was quite hard to get a handle on. It was hard to learn it from the books. We didn’t have videos back then because my Wan connection was a 56K modem. So videos now can make this a bit more easier to understand.

So that’s what I’m going to try to do here. So I’ll explain what all the different Wan technologies are, and I’ll also show you network diagrams that are going to show the different options that are used for deploying them in the real world. So things that we’ll cover here, we’ll talk about virtual private networks, we’ll talk about unleashed lines, will also cover MPLS, will cover PPPoE over DSL. Let’s get started.

2. WAN Overview

In this lecture you’ll learn what wide area networks are and how they compare to lands, local area networks and demands which are metropolitan area networks. So starting off with the definitions first and when you see this, it’s so simple that it’s kind of comically easy. But if you didn’t know the definitions and somebody asked you what is is a Wan? Then maybe you’re going to start trying to talk about different connection types and things like that. But the actual definition of a man and a Wan is super easy. So a local area network is a network that connects computers and other devices in a relatively small area, which will typically be a single building or a group of buildings. So if you’ve got a company, they own a building and they’ve got all their internal connections in there for that building, that is their local area network.

Or maybe it’s a university campus which is spread out over several buildings but all in the same small area. That would also be a local area network as well. A wide area network is a geographically distributed network that connects multiple local area networks together. So say we’ve got a company and they’ve got an office in New York, so they’ve got Vernon in New York, they’ve also got a building in Boston, so that’s Verwan in Boston and we want New York and Boston to have connectivity to each other. Well, we would need to have a wide area network to connect them together. That is our Wan. The other type of network that you’ll hear about is a man, which is a metropolitan area network.

This is a network that connects computers and other devices in a geographic area larger than a land but smaller than a Wan. You see what I mean about it being kind of comically simple about the definitions. So if you had a university campus and it’s all in one campus, that would be a land. But if there’s a university and they’ve got their main campus, which is in, say, New York, and they’ve maybe got a smaller campus, which is 5 miles away, also in New York, so within the same city and they connected those two campuses together, each campus would be its own land. And the connection that connected the two campuses together would make up a man, a metropolitan area network. Now you won’t hear mans being used so much the definition as you do with Lands and Wands. So that scenario there where we had the two campuses within the same city and we connected them together, you could describe that either as a Wan or you could describe it as a man as well. So the term man is not so commonly used. So looking at, again a bit more detail on the differences. So this is something that we covered in an earlier section when we spoke about our lands. So our land network here, it’s for a small building. So we’ve got a collapsed distribution and core layer. So we’ve got redundancy here.

So we’ve got a couple of redundant routers which connect to the wide area network, which connect to our other offices. Also we’re going to want to connect to the Internet as well. And then that goes down to a pair of redundant distribution and core layer switches and then that goes down to our access layer where our end users get plugged into the network. So this would be a local area network. We can also have the core, the distribution and the access layer split out into three separate areas like you see here. This would be for a larger local area network. We’re still going to have our routers on the outside here connecting us to the Wan.

That goes down to a pair of core layer switches and that goes down to a pair of distribution layer switches which are in each different building in the campus. And then again, we have our end host connected in at the axis layer. So it’s a couple of different ways you can design your local area network depending on how big it is for our wide area networks. That’s just where we connect our different local area networks together. So we’ve got a land in New York, we’ve got a land in Boston. We connect them together so that our users have got connectivity across the different sites and that is our wide area network. Now, there’s loads of different ways we can design and build our one and that’s what’s going to be covered throughout the rest of this section.

3. VPN – Virtual Private Networks

In this lecture you’ll learn about the different Wan connectivity options and there’s multiple wide area network options available. Not all options are going to be available in all locations. It really depends what region, what country you’re in. What is commonly used in one region may be considered legacy in another. Like you might be in one part of the world where frame relay connections are still being used, but in other countries that would be considered legacy. Also, different providers will use different terminology. Here I’m going to use the terminology that Cisco use for the CCNA exam. So looking first at our primary one connectivity options, and when I say a primary option, this is going to be used by a corporation for their main connectivity to the Internet or to their other offices.

So the options here are leased lines, MPLS, multiprotical label switching, and satellite. And I’m going to have separate lectures for these later to give you more detail on them. Now if it’s a really large company, they might actually own the entire Wan infrastructure, but far more often your Wan connections are going to be offered by a service provider. So what options are available? It really depends what country you’re in and what the service provider is there can do with these primary connections. The service provider will typically provide an SLA, but it’s a service level agreement and it’s going to have guarantees for the uptime of the line and also for the traffic quality, meaning the delay and the loss on the link list. Lines and satellite can be used for connectivity to the Internet, for direct connectivity between offices and or connectivity a between offices over VPN. MPLS uses a shared core infrastructure at the service provider, so it can be used for connectivity to the Internet and or connectivity between offices over VPN. If it was a really large company and they owned their own MPLS infrastructure, that could also give direct connectivity between offices.

Okay, so those were our primary options. Again, we’re going to cover those in more detail later on in this section. Optical fiber is more suitable for long distances than copper wire, and it’s commonly used for service provider backhaul connections, meaning the connections between a service provider’s main locations, so those are internal to the service provider, require a lot of bandwidth. But optical fiber services can also be offered to the service provider’s customers. And in North America you’ll often see this being described as FTTx services. That’s fiber to the home, to the premises, the building and the neighborhood. Sonnet in North America and SDH in the rest of the world are the standards used in service provider optical fiber networks. So you can see the terminology you get sonnet, Sts and OC can be used basically interchangeably.

Sts One or OC One gives 51. 84 megabits per second up to Sts 192 for example, giving nine nine 5328 megabits per second. So really high bandwidth and in rest of the world. It is using SDH STM. So those are typically used for service provider backhaul connections, definitely the larger bandwidth ones. But if you are a large enough organization, you can also be using optical fiber with high bandwidth for your connections between your offices. DWDM is dense wavelength division multiplexing, and it combines or multiplexes multiple optical signals into one optical signal transmitted over a single fiber strand. And the way it works, the way it does the multiplexing is that each signal is assigned a different wavelength because you’ve got now the multiple signals that would normally require different fiber strands, that allows more capacity and more bandwidth to be added to existing infrastructure without requiring expensive upgrades.

And DWDM is used in all modern long haul optical connections in the service providers. Many service providers delayed optical fiber cabling in the past and then found that they didn’t actually need it. And DWDM was a major reason for this because it did provide much more bandwidth with much less actual cabling. So there is a lot of unused cabling out there and that is referred to as dark fiber. It’s dark fiber because it hasn’t been lit up and it is possible, depending on where you are in the world, that maybe you can buy dark fiber from a service provider as an organization to use for your own Wan links. We will also have a look at our Wan backup and small office solutions.

So less expensive options which are often aimed at home user Internet access, can also be used as Internet VPN. Wan Backup Options in corporate environments there will typically be no corporate level SLA with those services because they’re going over the Internet and the service provider can’t control what happens there. These can be used as the primary one connection method to the corporate network from smaller offices and for home users.

So leased lines, MPLS and satellite connections, they’re more expensive. So in a large office we would use one of those and we’d probably use a backup solution there as well. If we’ve got a small office with just a handful of users there, maybe we can’t justify using one of those more expensive options. So we would use one of these instead. Our options here are DSL digital subscriber line cable and wireless.

For example, 4g So those are the kind of options that you knew about already because you can get them at home. There’s also legacy options as well, like PSTN going over the public switch telephone network. If you’re as old as me, you’ll remember those old 56K dial up modems that would be using the PSTN for your wand. Obviously nobody would use those anymore. There was also Istn, which is integrated services, digital network. This is similar using those 56K modems, but it was aimed at the corporate market and it’s got higher bandwidth than a single analog phone line.

Other options frame really frame really is still used in some parts of the world, but in western countries it’s usually seen as a legacy option. Also ATM asynchronous transfer mode, similar characteristics to Frame Relay and even older X 25. So these are legacy as far as Cisco is concerned. But like I said right on the first slide, it really depends where you are in the world about what options will be available, maybe where you are. The service providers don’t offer MPLS, but they still do offer Frame Relay. Okay, the last thing to cover here is our Wan interface cards. Routers will typically come with onboard ethernet ports, and additional Ethernet interface cards can be added if you need more ports. Ethernet is commonly used for Wan connections today.

Other Wan interface types are modular and fit into a spare slot on the router. And there’s many, many different types of Wan interface cards. You’ll see some examples coming up on the next slide. Part numbers for different cards can be very similar, and different cards are compatible with different router platforms. So be very careful when selecting your card. It’s really easy to order the wrong one. To give you an example of that, up on the top here we’ve got a couple of serial cards. We’ve got the WIC two T, which is compatible with 1700 and the 2600 platforms. And then next to that we’ve got the HWIC two T, which is compatible with the 1819, 2829, 38 and 3900 is ours. So looking at these two, they look exactly the same. They’re both for the same type of connection, which is serial. So we would often use these for slower speed released lines or for Frame relay.

But one fits into one type of platform, the other fits into other platforms. And if you order a Wick two T instead of the HWIC two T, then it won’t work. So be really careful when ordering because often there’s just like a single letter or number difference, but it’s not going to have compatibility. Down in the bottom left, this is for the newer model routers before 1000 series ISR. And this is a NIM module, so it’s actually a larger module than the WIC modules. Here we’ve got the NIM two MFT, T one, E one, so it’s got two T one or E one ports. You can configure them as either. This can be used for data like over at least lines. We could also use this for TDM voice calls going to the public switch telephone network. I’ll speak about that a bit more when we do the least lines lecture.

And down in the bottom right we’ve got a Nimvab A, which is also for the 4000 series is ours, and that is a DSL card. So you can see particularly from the two at the top part numbers can be very similar. Be careful when you order. To give you a story about that, I worked for a company before and we were opening up a new office in Africa and it was easier to source the equipment in the UK. So we bought the equipment in the UK and the office in Africa.

It was going to have PCs there and also IP phones as well. So we needed switches that provided power for the IP phones. And what happened was the person that ordered it ordered non poe switches. So we had 30 pieces of routers and switches in the warehouse in Aberdeen and it was just about to get shipped out to Africa, and luckily somebody noticed the mistake and we were able to get those replaced. But if they’d been shipped to Africa, that would have been a really, really expensive, career limiting mistake. So do be careful when you’re ordering interface cards or routers or switches. OK, see you in the next lecture.

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