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## Re: Teaching/developing troubleshooting skills

• From: Edward B. Dreger
• Date: Sat Jun 26 05:33:13 2004

```DG> Date: Fri, 25 Jun 2004 20:04:38 -0700
DG> From: Darrell Greenwood

[ editted for brevity ]

DG> The 5 day course can be boiled down really to one concept
DG> that can be taught in 5 minutes... "binary search".

Every half-decent programmer knows O(log(N)) is one's friend
unless the scalar coefficient is large.  A good way to
demonstrate its efficiency is:

* Have someone pick an integer between 1 and n, inclusive
* Make guesses, going "higher" or "lower" according to the
number-holder's feedback.

The uninformed are surprised that one can always guess the number
from 1 to 1000 in ten iterations or less.

DG> The reason I am writing this note is as I went through a
DG> career of troubleshooting I was surprised at the number of
DG> colleagues who had no concept of "half-splitting" and used
DG> "linear" or "random" techniques to determine test
DG> points/tests with a corresponding dramatic reduction in
DG> effectiveness.

Good point.

[ below text in response to nobody in particular ]

It's also important that one avoid:

* The faulty assumption there is but one problem
* Incorrectly-formed causal relationships (NANOG-L has some
examples of these)
* Making too many changes in one iteration
* Attempting to tackle a system with more unknowns than are
absolutely necessary.

A certain amount of troubleshooting can be taught, but IMHO it
requires a self-driven person with intuitive reasoning.

Finally: Apprenticeship.  Have the novices follow along when
experts work actual cases.  A certain amount of troubleshooting
is developing the intuition to make informed guesses -- e.g.,
"some idiot broke pmtud" -- and develop good leads without having
to search methodically through the entire problem space.

Eddy
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