From: Anthony Sequeira (terry.francona@gmail.com)
Date: Wed Nov 30 2005 - 00:26:33 GMT-3
I have noticed many questions about this topic lately and I thought I would
put my two cents in for the group. Comments, critiques, and additions are
certainly encouraged. I will not, however, hire a temporary employee to help
field responses. ;-)
You can turn on dampening for an interface participating in RIP, OSPF,
EIGRP, IS-IS, or BGP and you can track interface "flaps" - having the IOS
remove the interface from routing if a certain penalty value is reached. The
values that you can set for this feature include:
Suppress Threshold - value that triggers dampening of the interface - you
must EXCEED this value to trigger dampening - DEFAULT IS 2000
Half-Life Period - the accumulated penalty is reduced by half each half-life
period; DEFAULT IS 15 SECONDS
Reuse Threshold - value that triggers the route coming out of dampening;
DEFAULT IS 1000
Max Suppress Time - max time that a route can be suppressed - DEFAULT IS 60
SECONDS
One value that you can not set is:
Penalty - (this number is not shared with you in the config guide - only the
command ref) - 1000
So let's say that I want to dampen an interface should it flap 4 times in 45
seconds....will the default values do this? I do no think so....watch.....
5 seconds - flap - penalty is increased to 1000
8 seconds - flap - penalty is increased to 2000
15 seconds - HALF LIFE - penalty decreased to 1000
20 seconds - flap - penalty increased to 2000
30 seconds - HALF LIFE - penalty decreased to 1000
35 seconds - flap - penalty increased to 2000
Notice that we just had our four flaps within 45 seconds - but we never
exceeded the Suppress Threshold. Decreasing the Suppress Threshold and
leaving all other values at defaults would do the trick I believe.
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