Re: OSPF SPF timer and interface dampening

In two words:

1) Event dampening suppresses event generation and effectively
prevents interface state changes and new LSA generation/prefix
withdrawl. This in turn stops excessive SPF calculations of EIGRP
query propagation.
2) OSPF has its own adaptive throttling features (LSA/SFP throttling)
I used to write about that in the past:
http://blog.ine.com/2009/12/31/tuning-ospf-performance/

As for the difference between (1) and (2), event dampening is a
feature that is independent of the upper-level protocol (e.g. OSPF,
RIP, BGP, ISIS) etc, while SPF throttling is specific to OSPF and
IS-IS. There is actually a small hierarchy of suppression features:
physical debouncing (e.g. carrier delay) -> interface dampening ->
protocol specific features (e.g. SPF throttling).

Selecting optimal values for every level of hierarchy is non-trivial
task, based on common sense, experimentation, "results from the past",
and mostly on the desired goals (e.g. fast convergence or high
stability). Discussing these topics is totally outside the scope of a
small post :)

2010/5/3 Abiola Jewoola <biola_y2k_at_yahoo.com>:
> Nice article guys!
>
> But what about preventing spf calculations like Chris asked
>
> Regards
> Abiola
>
> --- On Mon, 5/3/10, Joe Astorino <jastorino_at_ipexpert.com> wrote:
>
> From: Joe Astorino <jastorino_at_ipexpert.com>
> Subject: Re: OSPF SPF timer and interface dampening
> To: "Petr Lapukhov" <petr_at_internetworkexpert.com>
> Cc: "christopher hernandez" <chrish711_at_gmail.com>, ccielab_at_groupstudy.com
> Date: Monday, May 3, 2010, 7:19 PM
>
> Our latest blog on IP Event Dampening may also be of some use to you
> Chris : ) I hope it can help shed some light on the topic along with
> Petr's article! I prefer to think about it using 7th grade math
> though...
> http://blog.ipexpert.com/2010/04/19/ip-event-dampening-using-7th-grade-math/
>
> On Mon, May 3, 2010 at 9:53 PM, Petr Lapukhov
> <petr_at_internetworkexpert.com> wrote:
>> Hi,
>>
>> Thinking about your question I came with a quick blog post that
>> provides some reasoning behid half-time time selection and event
>> dampening as a whole.
>>
>> http://blog.ine.com/2010/05/03/optimizing-ip-event-dampening/
>>
>> HTH :)
>>
>> --
>> Petr Lapukhov, petr_at_INE.com
>> CCIE #16379 (R&S/Security/SP/Voice)
>>
>> Internetwork Expert, Inc.
>> http://www.INE.com
>>
>> 2010/4/30 christopher hernandez <chrish711_at_gmail.com>:
>>> There is an interface that is constantly flapping. I would like to
> configure
>>> dampenning in that interface in a way to avoid SPF calculations. Could
>>> someone please provide the correct dampening configuration to accomplish
>>> that and why? (half, resuse, suppress limit, max time, etc).
>>>
>>>
>>> Thanks a lot for your help,
>>>
>>> chris
>>>
>>>
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>
>
>
> --
> Regards,
>
>
>
> Joe Astorino - CCIE #24347
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-- 
Petr Lapukhov, petr_at_INE.com
CCIE #16379 (R&S/Security/SP/Voice)
Internetwork Expert, Inc.
http://www.INE.com
Blogs and organic groups at http://www.ccie.net