Workshop

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Hour 21
Tell Me About Your Network: Network Analyzers
Sure, most network troubleshooting cases that you’ll encounter will be “elementary, my dear Watson”
(solvable by deductive reasoning alone). However, to solve your most hard-boiled network crimes, you’ll
need to get a wire tap to give you the evidence you need. Network analyzers provide a type of “wire tap”
that allows you to gather objective data about a networking problem.
Like a wire tap, network analyzers shouldn’t be used indiscriminately; you definitely want to use your
noodle before you use your analyzer. You should always formulate a theory before breaking out the
analyzer—otherwise, what are you looking for? (After all, it’s a big network out there.)
Still, when you run into a problem that needs an analyzer, it can be the difference between a stone wall
and a breakthrough. After you’ve formulated a theory, analyzers can prove your theory by providing you
tangible evidence to either sift through yourself or to give to a vendor for analysis.
What the Heck Is a Network Analyzer?
I have to smile every time I talk about network analyzers: I always think about a piece of network gear
reclined on a couch, with some Freudian white-bearded psychoanalyst asking it about its origins. As silly
as that seems, this picture isn’t far off—a network analyzer’s primary job is to listen while other network
gear talks.
Here are the two basic kinds of network analysis tools:
• Cable scanners (hardware analyzers)
• Packet sniffers (software analyzers)
A cable scanner’s primary job is to test the electrical characteristics of your network wire. As we
discussed in Hour 9, “Ethernet Basics,” CAT-V cable needs to have certain electrical characteristics,
without which you’ll get data link errors. A cable scanner will test any particular cable run “end to end”
and let you know if something is out of whack.
Some of the more sophisticated scanners will also listen to the signal on the wire to see whether there are
physical or data link problems on your network. For example, the only way to truly detect collisions on