[71943] in North American Network Operators' Group
Re: Teaching/developing troubleshooting skills
daemon@ATHENA.MIT.EDU (Edward B. Dreger)
Sat Jun 26 05:30:53 2004
Date: Sat, 26 Jun 2004 09:29:59 +0000 (GMT)
From: "Edward B. Dreger" <eddy+public+spam@noc.everquick.net>
To: nanog@merit.edu
In-Reply-To: <p06020401bd0296553087@[216.232.73.243]>
Errors-To: owner-nanog-outgoing@merit.edu
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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