From: Nick Griffin (ngriffin@sio.midco.net)
Date: Fri May 19 2006 - 17:02:11 ART
I have to agree, in testing this "dampening 30 1000 3000 60" did not
work for me, but "dampening 30" does. How many points could this be
worth in the lab? 2-3 at most, so I can't imagine too much more thought
needs to go into it. Probably a good thing to know tho.
Chris Lewis wrote:
> Dear All:
>
> I think this discussion is making it far more complex than need be.
>
> IMHO one cannot ignire the fact that it is an exponential decay mechanism in
> order to answer this question.
>
> The question asks that if three flaps occur within 30 seconds, the interface
> will be dampened. This is troublesome as it does not tell you at what times
> those flaps occur, which is a pretty important piece of information. So the
> way to read it is to ask yourself what parameters will cause the interface
> to be dampened no matter what the spacing of the flaps is?
>
> I would suggest that
>
> dampening 30
>
> Or something close to it, is all you need configure
>
> The penalty is always 1000, and the suppress limit is 2000 at default. Look
> at what happens in these use cases.
>
> If three flaps occur evenly spaced every 14 seconds. At t=0, the first flap,
> the penalty is 1000, after 14 seconds, it will have decayed to something
> around 750 (this is not exact), at t=14 the next flap happens and the
> penalty is now 1750, at t=28 this decays to something a little over 1000 and
> the next flap occurs to take it over 2000 to suppress the interface.
>
> If two flaps happen within the first second the penalty goes up very close
> to 2000, say 28 seconds later than the penalty will be coming down close to
> 1000, then the third flap occurs to take the penalty over 2000 to have it
> suppressed.
>
> A case where two flaps happen at the start of 30 seconds and the third at
> the end of 30 seconds is illustrated with the following configuration and
> debug.
>
>
> R2(config-if)#dampening 30
> R2(config-if)#^Z
> R2#deb
> *Mar 1 18:03:22.903: %SYS-5-CONFIG_I: Configured from console by console
> damp int
> interface debugging is on
> R2#
> *Mar 1 18:03:48.867: %LINK-3-UPDOWN: Interface Serial0/1, changed state to
> down
> *Mar 1 18:03:48.867: IF-EvD(Serial0/1): IP Routing reports state transition
> from UP to DOWN
> *Mar 1 18:03:48.867: EvD(Serial0/1): charge penalty 1000, new accum.
> penalty 1000, flap count 1
> *Mar 1 18:03:48.867: EvD(Serial0/1): accum. penalty 1000, not suppressed
> *Mar 1 18:03:48.867: IF-EvD(Serial0/1): update IP Routing state to DOWN,
> interface is not suppressed
> *Mar 1 18:03:49.867: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Serial0/1, changed state to down
> *Mar 1 18:03:49.867: IF-EvD(Serial0/1): IP Routing reports state transition
> from DOWN to DOWN
> *Mar 1 18:03:54.187: %LINK-3-UPDOWN: Interface Serial0/1, changed state to
> up
> *Mar 1 18:03:54.187: IF-EvD(Serial0/1): IP Routing reports state transition
> from DOWN to UP
> *Mar 1 18:03:54.187: IF-EvD(Serial0/1): update IP Routing state to UP,
> interface is not suppressed
> *Mar 1 18:03:55.187: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Serial0/1, changed state to up
> *Mar 1 18:03:55.187: IF-EvD(Serial0/1): IP Routing reports state transition
> from UP to UP
> *Mar 1 18:03:59.663: %LINK-3-UPDOWN: Interface Serial0/1, changed state to
> down
> *Mar 1 18:03:59.663: IF-EvD(Serial0/1): IP Routing reports state transition
> from UP to DOWN
> *Mar 1 18:03:59.663: EvD(Serial0/1): accum. penalty decayed to 793 after 10
> second(s)
> *Mar 1 18:03:59.663: EvD(Serial0/1): charge penalty 1000, new accum.
> penalty 1793, flap count 2
> *Mar 1 18:03:59.663: EvD(Serial0/1): accum. penalty 1793, not suppressed
> *Mar 1 18:03:59.663: IF-EvD(Serial0/1): update IP Routing state to DOWN,
> interface is not suppressed
> *Mar 1 18:04:00.663: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Serial0/1, changed state to down
> *Mar 1 18:04:02.399: %LINK-3-UPDOWN: Interface Serial0/1, changed state to
> up
> *Mar 1 18:04:02.399: IF-EvD(Serial0/1): IP Routing reports state transition
> from DOWN to UP
> *Mar 1 18:04:02.399: IF-EvD(Serial0/1): update IP Routing state to UP,
> interface is not suppressed
> *Mar 1 18:04:03.399: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Serial0/1, changed state to up
> *Mar 1 18:04:03.399: IF-EvD(Serial0/1): IP Routing reports state transition
> from UP to UP
> *Mar 1 18:04:17.171: %LINK-3-UPDOWN: Interface Serial0/1, changed state to
> down
> *Mar 1 18:04:17.171: IF-EvD(Serial0/1): IP Routing reports state transition
> from UP to DOWN
> *Mar 1 18:04:17.171: EvD(Serial0/1): accum. penalty decayed to 1182 after
> 18 second(s)
> *Mar 1 18:04:17.171: EvD(Serial0/1): charge penalty 1000, new accum.
> penalty 2182, flap count 3
> *Mar 1 18:04:17.171: EvD(Serial0/1): accum. penalty 2182, now suppressed
> with a reuse intervals of 34
> *Mar 1 18:04:17.171: IF-EvD(Serial0/1): update IP Routing state to DOWN,
> interface is suppressed
> *Mar 1 18:04:18.171: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Serial0/1, changed state to down
> *Mar 1 18:04:19.283: %LINK-3-UPDOWN: Interface Serial0/1, changed state to
> up
> *Mar 1 18:04:19.283: IF-EvD(Serial0/1): IP Routing reports state transition
> from DOWN to UP
> *Mar 1 18:04:20.283: %LINEPROTO-5-UPDOWN: Line protocol on Interface
> Serial0/1, changed state to up
> *Mar 1 18:04:20.283: IF-EvD(Serial0/1): IP Routing reports state transition
> from UP to UP
>
> R2#sho int damp
> Serial0/1
> Flaps Penalty Supp ReuseTm HalfL ReuseV SuppV MaxSTm MaxP
> Restart
> 3 1282 TRUE 11 30 1000 2000 120
> 16000 0
> R2#
> *Mar 1 18:04:39.911: EvD(Serial0/1): accum. penalty decayed to 1282 after
> 23 second(s)
> *Mar 1 18:04:51.171: IF-EvD: unsuppress interfaces
> *Mar 1 18:04:52.171: IF-EvD: unsuppress interfaces
> *Mar 1 18:04:52.171: EvD(Serial0/1): accum. penalty decayed to 971 after 12
> second(s)
> *Mar 1 18:04:52.171: EvD(Serial0/1): accum. penalty 971, now unsuppressed
> *Mar 1 18:04:52.171: IF-EvD(Serial0/1): update IP Routing state to UP,
> interface is not suppressed
>
> THis shows teh interface being suppressed after the third flap, then 1
> minute thirty seconds after teh first flap, the link is unsuppressed when
> the penalty falls below the default 100 figure.
>
> Chris
>
> On 5/19/06, Godswill Oletu <oletu@inbox.lv> wrote:
>
>> Andrew,
>>
>> Agreed, you are correct, but you are looking at it at the micro level, the
>> fact is, what you just explained is what will take place, the penalties
>> are
>> decreased exponentially. But if we are to apply the half life and
>> exponential Decay formular, everybody will argue and nobody will do it,
>> because it will bring in alot of variations and that formular can be so
>> weary and long, that is why thinking macro will help resolve the
>> problem.We
>> just close our eyes and make ourself to believe that, the penalty will
>> only
>> be cut in half at the half life value.
>>
>> If you want to apply, the half life exponential decay fornular I bet, you
>> will not be able to arrive at a concrete set of values that will
>> "guarantee"
>> that the interface will be dampened at exactly 3 flaps within 30 sec.
>>
>> Like in most things in mathematics and science, to retain our sanity, we
>> are
>> allow to borrow, we are allow to summarize and to view things and make
>> assumptions at the micro level eg:
>>
>> While is college, I have been in classes where the lecturer will be
>> solving
>> equations, and at many points, we will substitute one complex equation
>> into
>> another, and we will continue for tens of minutes solving this long
>> convoluting formula that will make you feel hungry and tire; at the end of
>> about one hour or more; we will hear the lecturer say "this value is so
>> Infinitesimally small that we can equate it to zero" before you know it,
>> various portion of that complex equation will start knocking themselves
>> out,
>> until the final result is either zero (0) or one (1). We have "wasted"
>> hours
>> just to proved that some set of complex convulating formulars are just
>> zero
>> or one. And that is true, everything in science and mathematics and
>> networking too is either 1 or 0.
>>
>> We all know that:
>> !
>> queue-list 1 queue 0 byte-count 2000
>> queue-list 1 queue 1 byte-count 3000
>> queue-list 1 queue 2 byte-count 1000
>> !
>>
>> Is all a LIE, your interface is not sending exactly 2000 bytes for queue
>> 0;
>> 3000 bytes for queue 1 and 1000 bytes for queue 2. But at the macro level,
>> because we are allow to borrow or if you average the output for the
>> interface over an extended period of time; we will agree that it is on the
>> average sending at that level.
>>
>> But looking, analyzing and trying to understand it at the micro level can
>> be insane at times.
>>
>> This is the formular for half exponential decay:
>>
>> A=Aob^t (where 0 <b<1) or
>> A=Aoe^kt (where k is a negative number representing the rate of decay).
>> In both formulars Ao is the original amount present at time t=0.
>> (from: www.mathwords.com)
>>
>> Who in his/her right senses will want to touch that formular with a long
>> stick before configuring dampening on an interface?
>>
>> HTH
>> Godswill Oletu
>>
>> ----- Original Message -----
>> From: "Edwards, Andrew M" <andrew.m.edwards@boeing.com>
>> To: "Godswill Oletu" <oletu@inbox.lv>; "Koen Zeilstra"
>> <koen@koenzeilstra.com>; <ccielab@groupstudy.com>
>> Sent: Friday, May 19, 2006 12:18 PM
>> Subject: RE: ip event dampening parameters
>>
>>
>> I suggest you lab this up. With "dampen 30 1000 3000 60" the interface
>> will not dampen in 30 seconds with 3 flaps..
>>
>> True, the half life is when the value is decayed by half its original
>> penalty. But since its an exponentially decaying algorithm, the penalty
>> begins decaying IMMEDIATELY.
>>
>> What this means is, if you flap the interface with dampening (dampen 30
>> 1000 3000 60) you will see the penalty at 1000 immediately, but then
>> querying the dampening for the interface again will indicate another
>> value like 893. And again, 773, etc. until at 30 seconds the value will
>> be 500 for the first flap.
>>
>> If you flap it a second time then the penalty will be the original
>> decayed penalty value at that moment PLUS the new penalty value (e.g.
>> 1000). And the exponential decay begins again. Query the interface and
>> you will see the penalty between 500 and 1500 and decaying fast. The
>> same holds true for a third flap.
>>
>> In short, a suppress value of 3000, as configured, will not dampen the
>> interface with 3 flaps in 30 seconds because the cumulative penalty will
>> be < 3000 at the half-life; guaranteed!
>>
>> HTH,
>>
>> Andrew Edwards
>>
>> CCIE #15334
>> Senior Network Engineer
>> 562-797-4454 desk
>> 800-946-4646 pin 6024349
>>
>>
>> -----Original Message-----
>> From: Godswill Oletu [mailto:oletu@inbox.lv]
>> Sent: Friday, May 19, 2006 6:53 AM
>> To: Koen Zeilstra; ccielab@groupstudy.com
>> Subject: Re: ip event dampening parameters
>>
>> Koen,
>>
>> Without going into alot of calculations, the answer to your original
>> question was straight forward and you were actually on the right path,
>> but instead of using a half life of 15 sec; a half life of 30 sec will
>> do the job..ie instead of:
>>
>>
>>> dampening 15 1000 3000 60
>>>
>> Using ....
>> !
>> interface fa0/0
>> dampening 30 1000 3000 60
>> !
>> Will be just fine...
>>
>> The penalty for each flag is 1000 and that does not change and there is
>> no configurable parameter to change it. The above dampenning policy
>> simply
>> means:
>>
>> * 1st flap, interface will get a penalty of 1000
>> * 2nd flap, the penalty will be 2000
>> * 3rd flap, the penalty will be 3000 and the interface will be dampened.
>>
>> If the 2nd or 3rd flap occurred after 30 sec, the culmulative penalty
>> will be less than 3000 and the interface will not be dampened.
>>
>> ***Note, the original question states that "dampen the interface if it
>> flaps
>> 3 times in 30 sec. period"
>>
>> You see that, there will be no need to dampen the interface unless all
>> three flagings occur within 30 sec and since the half life is pegged at
>> 30 sec, a penalty of 3000 accessed against 3 flaps is the key to
>> answering your original question.
>>
>> You might want to say..."What if the 3rd flap happens at the 30th sec.?,
>> well this is open to a wide variety of interpretation, which, I believe
>> the question does not want to exploit, because if a flap took place at
>> the 30th sec, two things will happen; a penalty of 1000 will be
>> accessed, and the cumulative penalty will be cut in half, now which will
>> take place first (accessing a penalty of 1000 or cutting the culmulative
>> penalty by half)? As you can see, this is another thread of its own.
>>
>> So 'dampening 30 1000 3000 60' is good enough, you can adjust the reuse
>> and max suppress vlaues, since the question is silent about them.
>>
>> HTH
>> Godswill Oletu
>>
>>
>> ----- Original Message -----
>> From: "Koen Zeilstra" <koen@koenzeilstra.com>
>> To: <ccielab@groupstudy.com>
>> Sent: Friday, May 19, 2006 4:31 AM
>> Subject: RE: ip event dampening parameters
>>
>>
>>
>>> resent with original subject for clarity.
>>>
>>> -----------------------
>>> You look like a million dollars. All green and wrinkled.
>>>
>>> ---------- Forwarded message ----------
>>> Date: Fri, 19 May 2006 06:54:40 +0000 (UTC)
>>> From: Koen Zeilstra <koen@koenzeilstra.com>
>>> To: "Edwards, Andrew M" <andrew.m.edwards@boeing.com>
>>> Cc: Valentijn van Veen <valentijn@icando.nl>, ccielab@groupstudy.com
>>> Subject: Re: your mail
>>>
>>> Hi,
>>>
>>> It's getting clearer by the minute fortunately.
>>>
>>> However the cummulative value of the second flap penalty should be
>>>
>> 1500 <
>>
>>> B < 2500. Since if it happens at t=30 (halftime) it is at its
>>> lowest (500 + 1000 = 1500). And right after the first flap: 1000 +
>>>
>> 1000 =
>>
>>> 2000.
>>>
>>> So within the 30 seconds another flap would be anything about 2000.
>>>
>> That
>>
>>> makes again dampening 30 with default 2000 as suppress value the best
>>> option.
>>>
>>> thanks,
>>>
>>> Koen
>>>
>>>
>>>
>>> On Thu, 18 May 2006, Edwards, Andrew M wrote:
>>>
>>> | Think of it this way... We know each flap is a penalty of 1000.
>>>
>> So...
>>
>>> |
>>> | The first flap is a penalty of 1000. With a half life of 30 seconds
>>>
>> the
>>
>>> | maximum penalty for the first flap at time = 30 sec. is 500. Let
>>>
>> A=500
>>
>>> |
>>> | The second flap is sometime between time =0 and time =30. So we can
>>> | deduce that the penalty from the second flap will be greater than
>>>
>> 500 at
>>
>>> | the 30 second mark but less than 1000. The second flap penalty
>>>
>> value is
>>
>>> | represented by B. We can safely say that 500 <= B <= 1000
>>> |
>>> | The third flap is sometime between the second flap and time = 30.
>>>
>> So we
>>
>>> | can again deduce that the penalty from the third flap will be
>>>
>> greater
>>
>>> | than 500 at the 30 second mark but less than 1000. The third flap
>>> | penalty value is represented by C. Again, we can safely say that
>>>
>> 500 <=
>>
>>> | C <= 1000
>>> |
>>> | What do we know then? We know that A = 500. We also know that B
>>>
>> and C
>>
>>> | cannot be any larger than 500.
>>> |
>>> | So the LOWEST total accumulated penalty in this scenario by equation
>>>
>> is:
>>
>>> |
>>> | F(x) >= A+B+C.
>>> | F(x) >= 500 + 500 + 500.
>>> | F(x) >= 1500
>>> |
>>> | IOW, the SMALLEST accumulated penalty with a 30 second half life is
>>> | 1500.
>>> |
>>> | If we use "dampen 30", then the default suppress value is 2000.
>>> |
>>> | Since we cannot say with certainty that the penalty is >= 2000; and
>>>
>> I
>>
>>> | don't want to memorize the equation for exponential decay, we must
>>> | change the default suppress penalty to a number >= 1500.
>>> |
>>> | That, or memorize the exponential decay function. 8)
>>> |
>>> |
>>> | Andrew Edwards
>>> | <<Picture (Metafile)>>
>>> | CCIE #15334
>>> | Senior Network Engineer
>>> | 562-797-4454 desk
>>> | 800-946-4646 pin 6024349
>>> |
>>> |
>>> |
>>>
>>>
>>>
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