What is a LAN?

Overview of the LAN

Simple LAN

Example Network Topology

So, What is a LAN?  A LAN, or local area network, is a collection of computers, various network capable devices like printers and XBox’s, and all the things required to connect all this stuff together.  This includes cabling, wireless access points, switches, routers, firewalls, and so on.

Normally, the LAN is restricted in size to something between a couple computers connected in a room and all the stuff at a single location.  Even if that location is as large as a University campus.

Sometimes people will refer to the services that run on a LAN (like file and printer sharing, web servers, authentication, etc.) as the LAN itself.  I think this is a misuse of the term and that it is more useful when designing and troubleshooting a network, to distinguish between the LAN and the services that run on it.

Related Terms

Here are some related and similar to LAN terms used in the networking field; just to give you context for the term LAN

  • When you need to talk about all the equipment that connect multiple sites together, it is normally called a WAN, or wide area network.
  • When you need to talk about a small network that connects, for example, your cell phone to its bluetooth headset, it is normally called a PAN, or personal area network.
  • If you are talking about the wireless part of you network it is called the WLAN, or wireless local area network.
  • If you are talking about multiple locations throughout a city that are networked together it is called a MAN, or metropolitan area network.
  • If you are talking about a bunch of storage devices that are all networked together to look like one large heap of storage it is called a SAN, or storage area network.
  • If you are talking about segments of a LAN that “virtually” cluster machines together even if they are geographically separated it is called a VLAN, or virtual local area network.

Parts and Pieces

Lets talk a minute about the “all the things required to connect all this stuff together” part of a LAN.  A LAN of any size has lots of hardware that links all the computers on the LAN together.  Even your little setup at home will have each of these parts; they will just be at a smaller scale and, often, merged into one do-it-all device.  In large environments each or the following is normally a specialized and separate device.  The cliff-notes list of LAN parts and pieces is:

  1. Switch
  2. Router
  3. Firewall
  4. Wireless Access Point
  5. Copper and Fiber Cabling

Of the devices listed above, the most common device in a LAN is going to be the network switch.  The switch is what is on the other side of the network cable that you have in your office.  If you are using wireless, the wireless access point your computer is talking to is then plugged into a switch.  The switch is everywhere and is going to be a big part of networking for some time to come.  For the interested, in another post I go into some detail on the difference between a router and a switch.

Topology

Just like with size, a LAN can come in many different shapes and layouts.  There is the bus, star, ring, mesh, and others.  About.com has a nice write up about these various topologies.  I want to take this moment to focus on just one topology, the star.

The star topology is by far the most common layout you will find in computer networking today.  In a star topology you have a hub and spoke layout, where client computers, Wii’s, Tivo’s, Apple TV’s, printers, whatever… are all connected directly to a central device.  So, in this structure, every packet between your computer and your printer goes through the central device.  The central device is most commonly a switch, but could also be a wireless access point, a firewall, another computer, whatever.

As a network grows you will need to create more stars and link those stars together by plugging the central part of one star into the central part of another.  This “star of stars” structure is the form that most LAN’s take.

Further Reading

I also want to note that Wikipedia does a great job of covering all the details of what a LAN is and the history around local area networks.  In this article I wanted to just give you the necessary information to get a basic operational answer to the “what is a LAN” question.  If you want to know a little more about the history, less common network configurations, etc. check out the Wikipedia article.

2 Responses to What is a LAN?

    • Hey James,

      Yes. That is still a LAN.

      The switch is really just the most common way of interconnecting devices in a LAN. LAN, in general, is really more about the area that the setup covers then the details of the setup… sort of. Since your wireless AP/router and all the computers that use it are in a single location it is a LAN.

      Now lets take a location like a house. All the stuff that is interconnected in the house can be taken together as a LAN. But if you connected the house with another house across town using a leased line (like fiber, a T1, etc.) from a company then you would have 2 LAN’s connected through a WAN.

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