Re: BGP Dampening Reuse Timer from Tech Guy on 2010-08-31 (Ccielab archives 08/2010)

From: Tech Guy <autechguy_at_gmail.com>
Date: Wed, 1 Sep 2010 11:54:53 +1000

Andrian,

The reuse timer seems to be reset back to 11 minutes minutes once it
reaches 0. It is not related to the half-time of 15 minutes. (see
below outputs for further details)

Everyone can telnet to an open looking glass and have a try. I can not
lab this, as the IOS I have for Dynamips do not show the "reuse"
timer. But the same behaviour is seen on various platforms and IOS.

route-views.optus.net.au>sh ver | in IOS
IOS (tm) 7200 Software (C7200-P-M), Version 12.0(32)S13, RELEASE SOFTWARE (fc3)

(AT&T looking glass route-server.ip.att.net IP address 12.0.1.28 )
route-server>sh ver | in IOS
Cisco IOS Software, 7200 Software (C7200-JS-M), Version 12.2(31)SB10,
RELEASE SOFTWARE (fc2)

Another Production router
Cisco-7606>sh ver | in IOS
Cisco IOS Software, c7600s72033_rp Software
(c7600s72033_rp-ADVIPSERVICESK9-M), Version 12.2(33)SRB6, RELEASE
SOFTWARE (fc1)

route-views.optus.net.au>sh ip bgp 89.25.60.0/23
BGP routing table entry for 89.25.60.0/23, version 52091189
Paths: (3 available, no best path)
  Not advertised to any peer
  7473 3356 701 12301 9070 31340, (suppressed due to dampening) (history entry)
    202.160.242.71 from 202.160.242.71 (202.160.242.71)
      Origin IGP, localpref 100, external
      Community: 7473:12165
      Dampinfo: penalty 4648, flapped 15 times in 00:16:53, reuse in 00:06:43
  7474 7473 3356 701 12301 9070 31340, (suppressed due to dampening)
(history entry)
    203.13.132.53 from 203.13.132.53 (172.26.32.13)
      Origin IGP, localpref 100, external
      Community: 7473:12165 7474:1403
      Dampinfo: penalty 3719, flapped 12 times in 00:16:51, reuse in 00:01:43
  7474 7473 3356 701 12301 9070 31340, (suppressed due to dampening)
(history entry)
    203.13.132.35 from 203.13.132.35 (172.26.32.42)
      Origin IGP, localpref 100, external
      Community: 7473:12165 7474:1403
      Dampinfo: penalty 3719, flapped 12 times in 00:16:51, reuse in 00:01:43

route-views.optus.net.au>sh clock
01:34:45.684 UTC Wed Sep 1 2010
route-views.optus.net.au>sh ip bgp 89.25.60.0/23
BGP routing table entry for 89.25.60.0/23, version 52091189
Paths: (3 available, no best path)
  Not advertised to any peer
  7473 3356 701 12301 9070 31340, (suppressed due to dampening) (history entry)
    202.160.242.71 from 202.160.242.71 (202.160.242.71)
      Origin IGP, localpref 100, external
      Community: 7473:12165
      Dampinfo: penalty 4319, flapped 15 times in 00:18:34, reuse in 00:05:03
  7474 7473 3356 701 12301 9070 31340, (suppressed due to dampening)
(history entry)
    203.13.132.53 from 203.13.132.53 (172.26.32.13)
      Origin IGP, localpref 100, external
      Community: 7473:12165 7474:1403
      Dampinfo: penalty 3455, flapped 12 times in 00:18:32, reuse in 00:00:13
  7474 7473 3356 701 12301 9070 31340, (suppressed due to dampening)
(history entry)
    203.13.132.35 from 203.13.132.35 (172.26.32.42)
      Origin IGP, localpref 100, external
      Community: 7473:12165 7474:1403
      Dampinfo: penalty 3455, flapped 12 times in 00:18:32, reuse in 00:00:13

route-views.optus.net.au>sh clock
01:35:09.856 UTC Wed Sep 1 2010
route-views.optus.net.au>sh ip bgp 89.25.60.0/23
BGP routing table entry for 89.25.60.0/23, version 52091189
Paths: (3 available, no best path)
  Not advertised to any peer
  7473 3356 701 12301 9070 31340, (suppressed due to dampening) (history entry)
    202.160.242.71 from 202.160.242.71 (202.160.242.71)
      Origin IGP, localpref 100, external
      Community: 7473:12165
      Dampinfo: penalty 4252, flapped 15 times in 00:18:58, reuse in 00:04:43
  7474 7473 3356 701 12301 9070 31340, (suppressed due to dampening)
(history entry)
    203.13.132.53 from 203.13.132.53 (172.26.32.13)
      Origin IGP, localpref 100, external
      Community: 7473:12165 7474:1403
      Dampinfo: penalty 3402, flapped 12 times in 00:18:56, reuse in 00:10:49
  7474 7473 3356 701 12301 9070 31340, (suppressed due to dampening)
(history entry)
    203.13.132.35 from 203.13.132.35 (172.26.32.42)
      Origin IGP, localpref 100, external
      Community: 7473:12165 7474:1403
      Dampinfo: penalty 3402, flapped 12 times in 00:18:56, reuse in 00:10:49
route-views.optus.net.au>sh ip bgp dampening parameters
dampening 15 750 2000 60 (DEFAULT)
  Half-life time : 15 mins Decay Time : 2320 secs
  Max suppress penalty: 12000 Max suppress time: 60 mins
  Suppress penalty : 2000 Reuse penalty : 750

route-views.optus.net.au>sh ip bgp dampening parameters
dampening 15 750 2000 60 (DEFAULT)
  Half-life time : 15 mins Decay Time : 2320 secs
  Max suppress penalty: 12000 Max suppress time: 60 mins
  Suppress penalty : 2000 Reuse penalty : 750

On Tue, Aug 31, 2010 at 10:32 PM, Adrian Brayton <abrayton_at_gmail.com> wrote:
> I think that means 1 Minute and 4 seconds and once it reaches it's half-life the time starts over. That would be where you get the 10 Minutes and 50 seconds.
>
> 00:00:00 / Hours : Minutes : Seconds
>
> On Aug 31, 2010, at 8:24 AM, Carlos G Mendioroz wrote:
>
>> Adrian,
>> I think Tech Guy knows how "half life" works. So do I, you and Kambis.
>>
>> What I think he is pointing is that the output of the "sh ip bgp"
>> command is not consistent with the state of the route:
>>
>> "Dampinfo: penalty 1310, flapped 7 times in 00:27:30, reuse in 00:01:04"
>>
>> At that time, if pennalty is 1310 and half life is 15 minutes (as shown
>> after) there is no way it will take 1'4" to get below reuse threashold
>> of 750.
>>
>> The question was, as I read it, not about how this works, but about
>> the meaning of that "00:01:14" number. Do you know what it means ?
>>
>> -Carlos
>>
>> PS: When it becamos "historical" it does not become "less preferred". It
>> is as it was not there at all. Only reason you see it is for accounting
>> of the fact that is has been flapping.
>>
>>
>> Adrian Brayton @ 31/08/2010 9:13 -0300 dixit:
>>> I dont think it's a bug at all... It can take up to 30 minutes for a route to be unsuppressed if the default parameters are used.
>>>
>>> Suppress Value = 2000 / 15 Minutes later (Half-Life) / Suppress Value = 1000
>>>
>>> The suppression penalty decays at half the half life (7.5 minutes). So:
>>>
>>> First flap, penalty 1000 assigned, route placed in 'historical' category and becomes less preferred.
>>>
>>> Second flap, route has met the suppression limit of 2000 (a Cisco default). The route is dampened and no longer advertised to neighbors or accepted from neighbors.
>>>
>>> If route does not flap any further the penalty is decayed. The decay process begins 7.5 minutes after the route stabilized and decays exponentially every 5 seconds thereafter.
>>>
>>> Once the suppression penalty decays below 750 (the default value for the reuse threshold), the route is removed from dampened state and reused. The router parses the historical routes list every 10 seconds for reusable routes.
>>>
>>> HTHs a little.
>>>
>>>
>>> On Aug 31, 2010, at 6:51 AM, Carlos G Mendioroz wrote:
>>>
>>>> Sounds a lot like a bug to me.
>>>>
>>>> I guess you have the meaning ok, but the counter is self adjusting down
>>>> and may be an intermediate flap was not accounted for when the route
>>>> was already inactive.
>>>>
>>>> If you really want to know, you would have to make a lab, and
>>>> investigate its behaviour.
>>>>
>>>> -Carlos
>>>>
>>>> Tech Guy @ 31/08/2010 6:13 -0300 dixit:
>>>>> Hi Kambiz,
>>>>>
>>>>> That counter does decrease. However the value is not the time left
>>>>> till the route get de-dampened!
>>>>>
>>>>> If you look at my two output performed at different time then one
>>>>> shows penalty of 1310, reuse time of 01:04. The other one performed
>>>>> over one minute later showed penalty reduced to 1240 but reuse time
>>>>> increased suddenly to 10:50.
>>>>>
>>>>> That did not make any sense to me!
>>>>>
>>>>> On Tuesday, August 31, 2010, Kambiz Agahian <aussiecert_at_gmail.com> wrote:
>>>>>> Hi Huan,
>>>>>>
>>>>>> If I get your point correctly, I believe if you keep running the same command you will see that counter actually indicates the time as it elapses. It says you're 30 seconds away, 29 seconds away, 28 seconds away and so on.
>>>>>>
>>>>>>
>>>>>> Kambiz Agahian
>>>>>> CCIE Instructor/Consultant
>>>>>> M.Eng Telecom, CCIE# 25341, CCSI# 33326, MCSE, MCSA

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Received on Wed Sep 01 2010 - 11:54:53 ART

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