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Congratulations. You now know enough to reverse-engineer somebody elses undocumented network. Im so proud!
Youve probably noticed that documentation has been a major theme of this book. And why not? If youve turned ahead to this hour out of desperation, you may well be the victim of somebody elses undocumented network, and you have a good idea of how frustrating it can be. Fret not. This is where were going to comb the tangles out of that undocumented network and make it into a reliable and manageable beast. Its going to be humming along by the time you get through.
Grab a sharp pencil and take a deep breath, youre about to chart uncharted territory. Well start off with physical cable tracing and then move on to TCP/IP and IPX/SPX networks. (Why leave out NetBEUI? Remember, NetBEUI is a very simple, nonroutable protocolit cant be too complex, and a physical cabling diagram is probably enough.) Were going to assume that youve come into possession of a working network; its too tough to reverse-engineer a network thats broken. So, lets hurry and document it before it goes down. The network is up, and todays the day.
An unlabeled cable is a troubleshooters nightmare. After all, its in the wall, making it hard to know where the heck its going. Fortunately, most sites only have a certain number of electrical closets, and that narrows the number of locations that youll need to search.
One tool is an absolute must if youre trying to trace (and label) unlabeled cables. For under $100, you can get an inductive tone generator and an inductive tone tracer. (Jensen Tools, at www.jensentools.com, is one supplier, but there are others.) The theory behind an inductive tone generator is that it generates such a strong signal on the wire that the tracer can hear iteven without touching the wire. Very cool. This allows you to quickly and easily trace a wire from one end to another.
The operation of the generator/tracer pair is pretty simple. Follow these steps:
You now see why you put the generator at the workstation end. You want to limit the number of places you have to visit with the tracer.
Of course, if you have a very small site with only one or two hubs, you can always have a friend turn a computer off while youre looking at the hub. The hub port light that goes out belongs to the PC that just got turned off. Now you can label the wire appropriately. Still, inductive toners are a lot of fun to use.
Your first task in discovering how a TCP/IP network is laid out is to identify the glue of the networkthe routers! The easiest way to discover the routers on your network is to go to a functional workstation and check the TCP/IP configuration. Go to several in different locations, particularly if youre not sure whether you have multiple segments.
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