From: Roberto Fernandez (rofernandez@us.telefonica.com)
Date: Fri Apr 21 2006 - 18:18:34 GMT-3
Friends,
Even knowing what is it about; I'm having hard time figuring out how to
master the dampening configuration. It is especially hard since I don't
know which the ratio of the penalty decay is.
Let's talk about the standard scenario, where an interface (or a route
for BGP dampening) has to be suppressed after flapping given number of
times during a given interval. I don't have the answer, I'm just putting
some elements so someone can help me to find the way.
For easy calculations let use 3 times on 30 seconds (interface
dampening)
a- Let set the half life to 30 seconds.
b- Let consider a Fast Ethernet Interface, with keepalive 1 1 (period 1
sec retries 1)
c- From #b we assume that on a given moment the interface could take up
to 2 seconds to detect a loss of connectivity (if the interface goes
down just after a successful keepalive cycle) and no less than 1 second,
since it will send another keepalive before declaring itself down.
-------QUESTION #1------ How much can we assume penalty decays in a
second at the beginning of a half life period?
-------QUESTION #2------ How much can we assume penalty decays in a
second at the end of a half life period
-------QUESTION #3------ How much can we assume penalty decays in a
second at the middle of a half life period.
Having those answers we could figure out the extreme situations and pick
the right Suppress Value. Thos extreme situations are,
1- Three flaps at the beginning
2- Two flaps at the beginning, one at the end
3- One flap at the beginning two at the end
4- Three flaps equally spread
Any help will be really well appreciated.
Best Regards,
Roberto
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