Introduction to 5 Common Network Devices

There are lots of specialized networking devices in the world today.  If you look hard enough you can find a device specialized for any networking task.  In this article I want to ignore the obscure, uncommon, and long since past devices and cover just 5 major devices that are used today in the modern LAN.

5 Network Devices

Hub, Switch, Router, Firewall, WAP

So what hardware will I find when I go looking around the network?  What are the most common network devices that I should learn about to get started in networking?  Here’s the top 5 network devices you will need to know and love if you are going to work on a network:

  1. Hub
  2. Switch
  3. Router
  4. Firewall
  5. Wireless Access Point

The Hub

I have to be honest here, the hub is old school technology and not really used in modern networks.  I’ve included it here because you may run into it occasionally, but also because it is helpful in the next section (the switch) if you know what a hub is.

A hub is a device that simply spits out data it receives on one interface to all its other interfaces.  So, if a packet of data arrives on interface 1 of an 8 port hub, the hub will blindly copy that data out the interfaces 2 through 8.

This was useful in the early days.  It was a cheep and quick way to link up multiple computers.  The problem with hubs though is that only one computer can talk at a time.  If two computers talked at the same time, their traffic would get combined as it was echoed out the other interfaces.  This is called a collision, and it would corrupt the data being transmitted by both computers. So, each computer would have to try again, after a random time period.  This becomes a real problem when the network gets busy or when more then a hand full of computers are on a network.  A switch solves the collision issue.

The Switch

A switch is the device that is most likely on the other side of the cable your computer is plugged into.  In many respects it is the same as a hub, though it is different in one key way.  A switch only repeats traffic out ports it needs to rather then out all of its ports.

Switches come in lots of different shapes and sizes, depending on how much horse power you need.  The most common network switch is only 1U tall and is shaped kind of like a pizza box.  On the front of the switch will usually be 24 to 48 ethernet ports and a couple extra special ports that can be configured to use copper, fiber, or serial connections.  Switches have so many ports because the main point is to connect client computers to the network.

A switch is able to intelligently decide what ports to forward packets out of because it listens to the packets that it receives on each port and notes the source address in the packet.  By learning what port each MAC address is on it can forward packets it receives out that one interface rather then all its interfaces.  This one simple change has made a huge difference in the networking world, has enable networks to run as quickly as they do, and allowed them to scale to as large as they have.  For more detail on switches check out this article discussing differences between them and routers.

The Router

The router is the workhorse of the internet.  A router works like a traffic light between networks enabling the flow of data between them.  Without routers there would be no Internet.  You could connect a few computers together in a building, but no much beyond that.

Routers typically have fewer physical ports on them then switches.  They will also have more variety of ports including Ethernet, Fiber, ISDN, Serial, modem, etc.  Modern routers usually have “blades” or modules that you can put into them to introduce different types of ports.  They are designed this way because they are used to connect different types of networks together, so they need the right type of interfaces for the various networks that they will connect to.

A router works by looking at IP addresses, breaking them down into their parts (using a subnet mask), then deciding based on that information if it should forward the packet out one of its interfaces to another router, to the packets destination computer, or if it should just drop the packet all together.  If the packet is forwarded on to another router, the decision process is repeated by that router.  This happens over and over again until the packet reaches it destination.  Each time the packet is handed off to another router it is called a “hop”.  You can see this process happen by using the traceroute (or tracert depending on your OS) command line tool.  You will see a response from each router your packet passes through if you issue a command like:

The Firewall

A Firewall is a security device that is designed to filter traffic that enters or exits your network.  Firewalls today are “layer 4” devices which means they can make decisions based on TCP and UDP ports in addition to IP addresses.  Because a firewall can block specific network ports, they are most often used to prevent inbound attacks directed toward your computer systems.  So they typically live at the edges of a network.

You can, for example, use a firewall to allow http traffic to your web-server from the internet but deny all other traffic to it.  That way, you prevent unauthorized people from ssh’ing or using remote desktop to access your web-server, but still allow the world to have access to the web content you want to host on that server.

Firewalls typically come in the form of a 1U to 4U tall device with only 3 or 4 network ports on them.  They only need a few ports because you don’t connect lots of client computers to them like a switch, but rather, aggregate traffic together and then send it through the firewall.

Some modern firewalls that have only recently come to market are called layer 7 firewalls.  These firewalls look deeper into network packets and attempt to figure out what is inside the packet regardless of what network port it is on.

The Wireless Access Point

Wireless Access Points (AP or WAP for short), like switches, are primarily focused on connecting client computers to the network using short range radio waves.  As of this writing, you can get wireless access points that operate using various standards including 802.11b, 802.11g, 802.11a, 802.11n, and 802.11ac.  These standards run in either the 2.4GHz or 5GHz frequency range and have various encryption capabilities and transmit speeds.

Wireless AP’s come in various shapes and sizes.  Some with lots of antenna on them and others with the antenna built into the shell of the AP.  They are typically the size and shape of a thick hard-bound novel and are designed to mount onto walls or on drop ceiling.  Most enterprise wireless AP’s can be connected to the network through an ethernet port.  They are typically powered through that same ethernet port using a technology called power over ethernet (PoE).  With PoE you don’t have to run power to the location you want an AP to be in, just a data port.

The Conclusion

These 5 devices: the hub, switch, router, firewall, and wireless AP will comprise the vast majority of the network equipment in any given LAN out there.  There are other devices you will see like modems, CSU/DSUs, Transceivers, Transponders, Bridges, Taps, GBICs, SFPs, etc.

Don’t worry about this other stuff right now.  You can learn about each of those devices as the need arises.  Right now, as you learn about networking, focus on the 5 devices mentioned in this article.  A good area to focus on next would be the differences between routers and switches.

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