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When I am reading some networking books, they often define a LAN as a set of connected computers across a building, campus floor, home, etc. However, I think this is pretty vague. What exactly defines a LAN? i.e. when looking at a network topology, how can you identify a LAN?

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Local would by definition be anything that's not "remote". Which then extends the question to what's "remote". One safe-ish way to go is anything that's not connected via a bridge/router/gateway. –  Marc B Jan 9 '12 at 4:57

3 Answers 3

It is a pretty generic term. Any Local Area Network can consist of a number of computers <2 connected by a means.

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I'd say it has at least a bit to do with the trust that you can afford to a physically restricted network, as well as shared resources (like internet connections). –  bdares Jan 9 '12 at 4:55
    
Thanks, but that really doesn't answer my question, since I was wondering what the precise definition of a LAN is :) –  jasonbogd Jan 9 '12 at 4:56

I found this nice definition on Wikipedia:

A local area network (LAN) is a computer network that interconnects computers in
a limited area such as a home, school, computer laboratory, or office building.
The defining characteristics of LANs, in contrast to wide area networks (WANs),
include their usually higher data-transfer rates, smaller geographic area,
and lack of a need for leased telecommunication lines.

So, the three points that you can count on to decide whether this is a LAN or not use:

  1. Smaller geographic area.
  2. Higher data rates.
  3. Lack of leased lines to interconnect its parts.
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There is no precise definition, nor would it be useful.

In some situations, it might make sense to speak of a LAN as one broadcast domain; in another situation it might mean every node in a building; in yet another, two buildings connected with fiber.

The wikipedia quote posted earlier will have to do.

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Exactly. If it's hard to decide whether a particular network is a WAN or a LAN, it would only be because neither term accurately described it. In that case, what would be the point of calling it one or the other? –  David Schwartz Jan 9 '12 at 10:03