Common Network Devices – CompTIA Network+ N10-006 – 1.1

| March 18, 2015 | 0 Comments


In your data center, you probably have equipment that you would commonly find in nearly any other networking environment. In this video, you’ll learn about some of these common networking devices.

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As you get into your networking career, you’re going to see a lot of different kinds of networking devices. And in your data center, some of them will be very common to you. In this video, we’re going to go through some of the most common network devices that you’ll find.

One of the foundational components of networking is the Ethernet hub. This hub is what we call a multi-port repeater, which means that any traffic going into one port on a hub is automatically sent to all of the other interfaces on that hub as well.

So you can plug into any place and see all of the traffic that may be traversing the network. We refer to this, in the OSI model, as an OSI Layer 1 device, since it’s really taking the signal and forwarding all of the signal to every other port regardless of what it happens to be.

When you’re connected to a hub, you are connected in half-duplex mode. That means that you can send information or you can receive information, but you can’t do both of those at the same time. We’re almost used to a full-duplex mode in today’s modern networks. Because we’re using switches.

But back when we were using hubs, we didn’t have the flexibility of having a full-duplex connection. That means that the more that we increase our speeds, the less efficient the network is going to be. Because as we’re sending, we’re going to have to wait for everybody else to finish what they’re doing so that we can finally send information.

You’ll also find that hubs really only come in two flavors– a 10 megabit and a 100 megabit version. Although there was a specification in Ethernet for higher speed hubs, the technology of switches had already come out, so no manufacturer invested any time in creating a gigabit hub. So if you do run into a hub, it’s either going to run at 10 or 100 megabit.

And hubs are a little bit outdated. They’re difficult to find today. There is some niche uses of these, especially in doing network management and network troubleshooting, but because they’re only running at 10 or 100 megabit, they have very limited use today.

When switching hardware was introduced, we quickly move from hubs to using switches. And if you’re connected to a network today, you’re undoubtedly connected to a switch. These switches are able to move information very quickly, because of the hardware inside of them.

This hardware is called an application-specific integrated circuit, and we refer to this as an ASIC. These ASICs are designed to move information across the network based on what the destination hardware address might be of a device. We call these OSI Layer 2 devices, because it’s using that data link address to determine where traffic goes.

This is a much more intelligent way of sending traffic than a hub, which simply sent all of the information to every single port on the device. Instead a switch is very specific. If information is destined for a particular interface, it sends that information to only that interface on the switch.

Another advantage of switching technology is that you can have a lot of interfaces on a single switch. Some very large enterprise switches can have hundreds of interfaces on one single chassis, which makes it perfect for putting in the middle of a network or in the middle of a data center.

Some switches can also provide power. So you can plug in your voice over IP phone or an access point, and all the power for that device is coming directly from the switch.

Some switches are designed with Layer 3 functionality, so they can effectively route information as well. At that point, we’re layering two devices together, a switch and a router inside the same device. And we tend to call those multi-layer switches, or Layer 3 switches, to designate that they can not only switch information, but we can also use them as a router as well.

Another common network device is a router. A router is designed to send information between different IP subnets. We will often refer to this as a Layer 3 device, because it’s making its forwarding decision based on the Layer 3 address, or the IP address, that might be within a network communication.

And that’s why you’ll hear people refer to a Layer 2 device as a switch and a Layer 3 device as a router. And as I mentioned, there are some switches that integrate routing functionality. So one part of the switch can perform forwarding decisions based on the Layer 2 address. And other parts of that switch will route and perform its forwarding decisions based on the Layer 3 address of that device.

These routers are often connecting IP addresses on Ethernet. But they can also be used to connect different network types as well. So you may be connecting a LAN with a WAN. Or you may be connecting a copper network to a fiber network. And you want to be able to route between those routers the perfect choice to use for that particular function.

Network security is also incredibly important. And that’s why another common device you’ll find on your network is a firewall. Traditional firewalls can filter information going through your network based on a port number. This would be an OSI Layer 4 TCP port number or UDP port number.

Some modern firewalls can filter information all the way up into Layer 7. They recognize the exact application you’re using and can make decisions on whether to allow or block that traffic based on the application that’s flowing through it.

Firewalls can also be used to encrypt information in and out of your network. If you need to connect to a remote side but you want to send everything to that remote site in a very secure way, you’ll find that many firewalls provide this IPsec encryption mechanism. And we’ll learn a lot more about that as we progress through this Network Plus course.

Firewalls can also be used to do things like proxy traffic. Not all firewalls provide this functionality. But it is something that you might commonly find in a firewall, so that you can stop all of the communication and instead have the firewall have that communication done on your behalf.

And then once the firewall receives an answer to that request, it then sends it to you internally. And this allows the firewall to effectively get in the middle of that conversation and make sure there’s nothing bad that might be traversing that particular link.

When we refer to firewalls, we’re talking about Layer 4 filtering. But it’s not unusual to see firewalls operating at Layer 3, becoming routers as well.

There’s many ways to connect firewalls. This is one of the most common ways you’ll find to plug in a firewall on your network, so that it’s not only the firewall protecting your network. it’s also the main router between the inside and the outside of your network.

Another common network device you may find is a wireless access point or while a WAP. If you’re working at home, you may be accustomed to seeing a wireless router. And it has the wireless antennas on the outside of it, but it’s also the router that’s used inside of your network.

In those particular cases, the wireless access point functionality is also built into the router. But we would refer to those more appropriately as wireless routers.

A WAP is something you might commonly see in a larger enterprise environment. It is simply a bridge. It’s extending an existing Ethernet network that is on a wired network into something that is wireless. And so it is an OSI Layer 2 device, because it’s making its forwarding decisions based on the Mac address or the data link address inside of those frames.

One of the mainstays of the common network device is the modem. Modem stands for modulator/demodulator. And it’s a way to take information that is digital, convert it into an analog form, send that through a medium, and on the other side, convert it back into a digital form that can be then used by the computing devices on the other side.

A very common modem uses standard phone lines. We connect up to the phone line, we’re sending audio signals, which are those analog signals across the phone lines. And on both sides of the connections, we have modems to convert those back into digital form.

It’s very common to see these days a modem being used on these plain old telephone systems, or these POTS lines, for things like backup and utility functions. The bandwidths that are allowed by these modems are very limited. So they’re really specifically used for a different type of utility function or something that doesn’t require a lot of bandwidth.

A more modern modem might be one that we find in our homes and our businesses that connect us up to a DSL network. These asynchronous DSL lines take the digital signals and convert them into an analog and send them over the DSL link to the other side.

You might also have, in your environment, a cable modem. Cable modems don’t work exactly like modulator/demodulator. But they do provide that bridging functionality that allows us to connect from our Ethernet network onto the cable modem network.

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Category: CompTIA Network+ N10-006

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