{"id":462,"date":"2012-02-10T20:36:32","date_gmt":"2012-02-10T20:36:32","guid":{"rendered":"http:\/\/microsoftgeek.com\/?p=462"},"modified":"2018-09-06T23:25:20","modified_gmt":"2018-09-06T23:25:20","slug":"networking-basics-part-2-routers","status":"publish","type":"post","link":"https:\/\/microsoftgeek.com\/?p=462","title":{"rendered":"Networking Basics: Part 2 – Routers"},"content":{"rendered":"

This article continues the discussion of networking hardware by talking about one of the most important networking components; routers.<\/p>\n

In the first part of this article series, I talked about some basic networking hardware such as hubs and switches.\u00a0In this article, I want to continue the discussion of networking hardware by talking about one of the most important networking components; routers.<\/p>\n

Even if you are new to networking, you have probably heard of routers.\u00a0Broadband Internet connections, such as those utilizing a cable modem or a DSL modem, almost always require a router. A router’s job isn’t to provide Internet connectivity though.\u00a0A router’s job is to move packets of data from one network to another.\u00a0There are actually many different types of routers ranging from simple, inexpensive routers used for home Internet connectivity to the insanely expensive routers used by giant corporations. Regardless of a router\u2019s cost or complexity, routers all work on the same basic principles.<\/p>\n

That being the case, I’m going to focus my discussion around simple, low budget routers that are typically used to connect a PC to a broadband Internet connection.\u00a0My reason for doing\u00a0so is that this article series is intended for beginners.\u00a0In my opinion, it will be a lot easier to teach you the basics if I am referencing something that is at least somewhat familiar to most people, and that is not as complicated as many of the routers used within huge corporations. Besides, the routers used\u00a0in corporations work on the same basic principles as the routers that I will be discussing in this article. If you are wanting a greater level of knowledge though, don\u2019t worry. I will talk about the science of routing in a whole lot more detail later in this article series.<\/p>\n

As I explained earlier, a router’s job is to move packets of data from one network to another.\u00a0This definition might seem strange in the context of a PC that’s connected to a broadband Internet connection. If you stop and think about it, the Internet is a network (actually it’s a collection of networks, but that’s beside the point).<\/p>\n

So if a router’s job is to move traffic between two networks, and the Internet is one of those networks, where is the other one? In this particular case, the PC that is connected to the router is actually configured as a very simple network.<\/p>\n

To get a better idea of what I am talking about, take a look at the pictures shown in Figures A and B. Figure A shows the front of a 3COM broadband router, while Figure B shows the back view of the same router.<\/p>\n

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\nFigure A: <\/strong>This is the front view of a 3COM broadband router<\/p>\n

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\nFigure B: <\/strong>A broadband Internet router contains a set of RJ-45 ports just like a hub or switch<\/p>\n

As you can see in the figures, there is nothing especially remarkable about the front view of the router.\u00a0I wanted to include this view anyway though, so that those of you who are unfamiliar with routers can see what a router looks like. Figure B is much more interesting.<\/p>\n

If you look at Figure B, you\u2019ll see that there are three sets of ports on the back of the router.\u00a0The port on the far left is where the power supply connects to the router.\u00a0The middle port is an RJ-45 port used to connect to the remote network.\u00a0In this particular case, this router is intended to provide Internet connectivity.\u00a0As such, this middle port would typically be used to connect the router to a cable modem or to a DSL modem.\u00a0The modem in turn would provide the actual connectivity to the Internet.<\/p>\n

If you look at the set of ports on the far right, you\u2019ll see that there are four RJ-45 ports.\u00a0If you think back to the first part of this article series, you\u2019ll recall that hubs and switches also contained large groups of RJ-45 ports.\u00a0In the case of a hub or switch, the RJ-45 ports are used to provide connectivity to the computers on the network.<\/p>\n

These ports work the exact same way on this router.\u00a0This particular router has a four port switch built in.\u00a0Remember earlier when I said that a router\u2019s job was to move packets between one network and another? I explained that in the case of a broadband router, the Internet represents one network, and the PC represents the second network.\u00a0The reason why a single computer can represent an entire network is because the router does not treat the PC as a standalone device. Routers treat the PC as a node on a network.\u00a0As you can see from the photo in Figure B, this particular router could actually accommodate a network of four PCs.\u00a0It\u2019s just that most home users who use this type of configuration only plug one PC into the router. Therefore\u00a0a more precise explanation would be that this type of network routes packets of data between a small network (even if that network only consists of a single computer) to the Internet (which it treats as a second network).<\/p>\n

The Routing Process<\/h2>\n

Now that I’ve talked a little bit about what a router is and what it does, I want to talk about the routing process.\u00a0In order to understand how routing works, you have to understand a little bit about how the TCP\/IP protocol works.<\/p>\n

Every device connected to a TCP\/IP network has a unique IP address bound to its network interface.\u00a0The IP address consists of a series of four numbers separated by periods.\u00a0For example, a typical IP address looks something like this: 192.168.0.1<\/p>\n

The best analogy I can think of to describe an IP address is to compare it to a street address.\u00a0A street address consists of a number and a street name.\u00a0The number identifies the specific building on the street. An IP address works kind of the same way.\u00a0The address is broken into the network number and a device number.\u00a0If\u00a0you were to compare an IP address to a Street address, then think of the network number as being like a street name, and at the device number as being like a house number.\u00a0The network number identifies which network the device is on, and the device number gives the device an identity on that network.<\/p>\n

So how do you know where\u00a0the network number ends and the device number begins? This is the job of the subnet mask.\u00a0A\u00a0subnet mask tells the computer where the network number portion of an IP address stops, and where the device number starts. Subnetting can be complicated, and I will cover in detail in a separate article. For now, let’s keep it simple and look at a very basic subnet mask.<\/p>\n

A subnet mask looks a lot like an IP address in that it follows the format of having four numbers separated by periods.\u00a0A typical subnet mask looks like this: 255.255.255.0<\/p>\n

In this particular example, the first three numbers (called octets) are each 255, and the last number 0.\u00a0The number 255 indicates that all of the bits in the corresponding position in the IP address are a part of the network number.\u00a0The number zero indicates that none of the bits in the corresponding position in the IP address are a part of the network number, and therefore they all belong to the device number.<\/p>\n

I know this probably sounds a little bit confusing, so consider this example.\u00a0Imagine that you had a PC with an IP address of 192.168.1.1 and a subnet mask of 255.255.255.0. In this particular case, the first three octets of the subnet mask are all 255. This means that the first three octets of the IP address all belong to the network number. Therefore, the network number portion of this IP address is 192.168.1.x.<\/p>\n

The reason why this is important to know is because a router\u2019s job is to move packets of data from one network to another.\u00a0All of the devices on a network (or on a network segment to be more precise) share a common network number.\u00a0For example, if 192.168.1.x was the network number associated with computers attached to the router shown in Figure B, then the IP addresses for four individual computers might be:<\/p>\n