Networking Devices – CompTIA Network+ N10-007 – 2.2

| April 7, 2018


If you walk into multiple data centers, you’ll probably start to see some similarities. In this video, you’ll learn about some of the most common network devices on today’s networks.

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If you’re an early user of Ethernet over twisted pair cabling, then you are probably connecting all of your devices with a hub. You’ll often hear a hub referred to as a multi port repeater. That’s because the operation of a hub means that any traffic going into one of these single ports of the hub will automatically be regenerated out of every other port that happens to be on that hub. This makes for a very simple forwarding mechanism. If traffic goes into the hub, it comes out of the hub on every other interface.

Since there are no forwarding decisions to be made inside of a hub, we often say that this is a device that’s operating at OSI layer 1. Because all devices are effectively sharing this network, that means that you can’t really have a full duplex connection to any other device on this network. All devices connected to a hub are going to be running at half duplex by default.

This also means that if more devices begin communicating more often, there will be an increasing number of collisions on this half duplex network, which means the more traffic increases, the less efficient this network will be. If you’re using a gigabit Ethernet network, then you’re not communicating using a hub. Hubs are only available if you’re running 10 megabit Ethernet or 100 megabit Ethernet.

As you can tell, the technology behind the hub is very simplistic. It’s not really designed for today’s high speed networks. Hubs are no longer manufactured, and it’s even difficult to find them these days on the secondary markets. Imagine if you had a switch that only had two ports on it. You had a network on one side of the switch and you had a network on the other side of the switch. In the early days of networking, you would have a bridge. A bridge is making forwarding decisions in software based on the MAC addresses of what happens to be on both sides of that bridge.

We would commonly use these bridges to connect two separate physical networks. These networks could be different typologies. So we might be connecting an Ethernet network to a token ring network by putting a bridge in the middle. But we might also use these bridges to connect similar typologies. You could take a very large Ethernet network and split it into two pieces to minimize the number of collisions that might be occurring.

Just like today’s modern switches, these older style bridges would make forwarding decisions based on the destination MAC address inside of a frame. A good example of a modern bridge that would be connecting different types of networks would be today’s wireless access points. You would have a wireless network on one side of this access point and a wired Ethernet network on the other. And you’re bridging between these two different typologies.

Our modern switches are an evolution from the older style bridges. Now we have devices with hundreds of interfaces on the front, rather than two or four that you might have on a traditional bridge. Also, a traditional bridge was making all of its forwarding decisions in software. On today’s switches, we are making all of these decisions in the hardware of these device using a technology known as ASICs, or Application Specific Integrated Circuits.

The forwarding decisions on our modern switches are exactly the same as the forwarding decisions that were made on the older style bridges. We’re looking at the destination MAC address and we’re forwarding the frame depending on where that MAC address needs to go. Our modern switches also have a number of additional features available to them. One good example is power over Ethernet, where you could plug in a device that requires power, and it can receive power directly from your network switch.

Some switches might also include the option to enable a routing functionality within exactly the same chassis. We call this functionality multi-layer switching. You might hear it referred to as a Layer 3 switch. That’s because there’s a portion of the switch that is performing the normal Layer 2 switching function. And there’s another portion of the switch that’s able to route between the different VLANs that are connected to that switch.

If a device is a router, then it’s forwarding traffic between different IP subnets. And it’s making its forwarding decisions based on the destination IP address that might be in that IP packet. If it’s a switch, then we’re making forwarding decisions based on a MAC address. That’s why we refer to routers as Layer 3 devices and switches as Layer 2 devices.

Routers will often connect different types of network typologies. On one side, you might have an Ethernet network running over fiber. And on the other side of the router, it might be a wide area network that’s running over copper. You generally don’t connect to any network these days without a firewall in place. Firewalls make decisions about whether traffic is allowed or not allowed through the network based on Layer 4 information. This might be a TCP or UDP port number.

Modern firewalls take that even higher and can look into the application that’s going across the network and make decisions on whether certain applications are allowed or not. We often refer to those as Layer 7 firewalls, or next generation firewalls. Many firewalls also provide other features. You could configure your firewall as a VPN endpoint at your main location, and configure another firewall as a VPN endpoint at a remote site. That will allow you to encrypt all of the traffic that flows between the main location and any of your remote sites.

Some firewalls can be configured as a proxy. So they’ll stop the network communication, make the request on your behalf, receive the response, make sure the response is appropriate for you to receive, and then send that traffic down to your workstation. Many firewalls can also be configured as a Layer 3 device. So they can route all of the traffic going in and out of the internet. So not only are they making security decisions based on Layer 4 UDP/TCP port numbers or Layer 7 applications, but they can also act as a router to send traffic between different IP subnets.

In many enterprise networks, we’d use wireless access points to be able to connect people to a wireless network. This is a little different than the wireless router you might have in a home office that has the router, the switch, the wireless access point, the firewall, and some other components within it as well. If you were able to pull out just the wireless piece, you would have a wireless access point.

As we mentioned earlier, a wireless access point is a Layer 2 device. It’s effectively a bridge between a wireless network and an Ethernet network. Many organizations will deploy many wireless access points throughout multiple floors of a building so that you can always be connected to the wireless network.

The device we call a modem is named after the modulator/demodulator function that is happening inside of this device. It’s very common to have modems, for example, on traditional phone lines. If devices in two locations needed to communicate, they could put a modem on each side and communicate over traditional phone lines. These phone lines have limited frequencies that are available, and therefore, there’s a limited amount of bandwidth that you could send between those two locations.

You’ll sometimes see modems used as a secondary, or backup, system to use the plain old telephone service or the POTS system to be able to communicate when all other forms of communication are unavailable. If you have DSL in your location, then you’re probably connecting to the DSL network using a DSL modem. If you have broadband internet from your cable company, they will provide you with a cable modem. Although technically, a cable modem is more of a bridge than it is a modem.

Sometimes you just need to convert between different types of network media. You don’t need to make forwarding decisions based on a Layer 2 MAC address or a Layer 3 IP address. You’re really just looking to change communication from running over a copper network to a fiber, and perhaps back again. In those scenarios, you might want to use a media converter. This is a good example of a media converter. This operates at OSI Layer 1. It’s simply changing the physical layer from a copper network to a fiber network or vise versa.

You might use one of these media converters if you need to extend the communication over a very long distance. We know that Ethernet can support up to 100 meters of communication. But if you need to go kilometers in distance, you might want to include a media converter to convert to fiber, extended it over that long distance, and then, perhaps, convert it back to copper on the other end.

You could also use this if you’ve been provided with fiber connections, but your switch only supports copper connections. You could use the media converter to convert from fiber to copper to provide that connection to the switch. This is usually an active conversion that’s taking place. So these devices very commonly need to be powered. You don’t generally see a device that’s converting from fiber to copper without some type of power source being connected.

In fact, it’s not uncommon to see rack-based media converters like this one that have central power supplies that provide power to all of these different media converters. Our wireless networks never seem to extend as far as we would like them to go. That’s because sometimes, we don’t have a choice where we put an access point. There might be a single room where we have an Ethernet connection, and that’s the only place available to plug in that wireless access point.

With a wireless range extender, you can increase the size of that wireless network. You can think of this as a wireless repeater that’s able to receive a wireless signal and then repeat that signal to a local area. Here’s how this wireless range extender might work in a typical house. Let’s say that your cable modem connection comes into a family room, and that’s the only place available to put a wireless access point. We’ll put it up high on this shelf. And it might cover a certain area of the house. But you can see that the kitchen and the master bedroom don’t have any coverage.

So we might install a wireless range extender right in the middle, maybe in this hallway upstairs. And when we turn that on, we can extend that wireless signal to cover more of this house just by adding that single repeater right in the middle of the communication. Remarkably, voice communication continues to be something we use even today. We are using different ways to communicate over these voice type networks by using voice over IP telephones or other types of software-based voice over IP endpoints.

This means we now have options. We can use voice over IP instead of using the traditional plain old telephone service or POTS lines. And we could use different types of platforms to be able to send this voice over IP communication. We could use a traditional physical handset, or we could use software that’s built into a browser, or on our mobile devices.

Category: CompTIA Network+ N10-007

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