Re: BGP Dampening Reuse Timer

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
>>>
>>>
>>> On Mon, Aug 30, 2010 at 11:36 PM, Tech Guy <autechguy_at_gmail.com> wrote:
>>> Hi GS,
>>>
>>> I have hard time understanding the meaning of the BGP dampening reuse
>>> timer in the "show ip bgp" command.
>>>
>>> Page 180 in the following document stated
>>> ftp://www.avmeiecuador.com/pub/manuales/cisco/pdfs/Cisco%20Bgp%20(Oreilly%200-596-00254-8).pdf
>>>
>>> "You can wait for the route to be used again when the reuse time
>>> arrives, or you can clear all flap dampening with the clear ip bgp
>>> dampening command."
>>>
>>> I think the reuse timer in the show ip bgp command is misleading.
>>>
>>>
>>> "Dampinfo: penalty 1310, flapped 7 times in 00:27:30, reuse in 00:01:04"
>>>
>>> With penalty of 1310, and half life of 15 minutes then it will take
>>> arround 12 minutes to get to 750 to be reused. It can not be 01min &
>>> 04 sec as stated in the "show ip bgp" output. Could you please explain
>>> what does "reuse in 00:01:04" really mean?
>>>
>>> Full output show below. It's taken on an Optus looking glass. You can
>>> pick up a dampened path via "sh ip bgp dampening dampened-paths" and
>>> "show ip bgp" to have a closer look at a paticular dampened prefix.
>>>
>>>
>>> Regards,
>>>
>>> Huan
>>>
>>>
>>>
>>> route-views.optus.net.au <http://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 <http://route-views.optus.net.au/>>sh clock
>>> 06:19:55.963 UTC Tue Aug 31 2010
>>> route-views.optus.net.au <http://route-views.optus.net.au/>>sh ip bgp 66.232.192.0/19
>>> BGP routing table entry for 66.232.192.0/19, version 51875338
>>> Paths: (3 available, no best path)
>>> Not advertised to any peer
>>> 7473 22773 30612 30612 30612 30612 30612 30612 30612 30612 30612
>>> 30612, (suppressed due to dampening)
>>> 202.160.242.71 from 202.160.242.71 (202.160.242.71)
>>> Origin IGP, localpref 100, valid, external
>>> Community: 7473:22015 7473:32265
>>> Dampinfo: penalty 1310, flapped 7 times in 00:27:30, reuse in 00:01:04
>>> 7474 7473 22773 30612 30612 30612 30612 30612 30612 30612 30612
>>> 30612 30612, (suppressed due to dampening)
>>> 203.13.132.53 from 203.13.132.53 (172.26.32.13)
>>> Origin IGP, localpref 100, valid, external
>>> Community: 7473:22015 7473:32265 7474:1403
>>> Dampinfo: penalty 1146, flapped 8 times in 00:47:18, reuse in 00:09:10
>>> 7474 7473 22773 30612 30612 30612 30612 30612 30612 30612 30612
>>> 30612 30612, (suppressed due to dampening)
>>> 203.13.132.35 from 203.13.132.35 (172.26.32.42)
>>> Origin IGP, localpref 100, valid, external
>>> Community: 7473:22015 7473:32265 7474:1403
>>> Dampinfo: penalty 1138, flapped 8 times in 00:47:18, reuse in 00:09:00
>>>
>>>
>>>
>>> route-views.optus.net.au <http://route-views.optus.net.au/>>sh clock
>>> 06:21:09.475 UTC Tue Aug 31 2010
>>> route-views.optus.net.au <http://route-views.optus.net.au/>>sh ip bgp 66.232.192.0/19
>>> BGP routing table entry for 66.232.192.0/19, version 51875338
>>> Paths: (3 available, no best path)
>>> Not advertised to any peer
>>> 7473 22773 30612 30612 30612 30612 30612 30612 30612 30612 30612
>>> 30612, (suppressed due to dampening)
>>> 202.160.242.71 from 202.160.242.71 (202.160.242.71)
>>> Origin IGP, localpref 100, valid, external
>>> Community: 7473:22015 7473:32265
>>> Dampinfo: penalty 1240, flapped 7 times in 00:28:45, reuse in 00:10:50
>>> 7474 7473 22773 30612 30612 30612 30612 30612 30612 30612 30612
>>> 30612 30612, (suppressed due to dampening)
>>> 203.13.132.53 from 203.13.132.53 (172.26.32.13)
>>> Origin IGP, localpref 100, valid, external
>>> Community: 7473:22015 7473:32265 7474:1403
>>> Dampinfo: penalty 1085, flapped 8 times in 00:48:32, reuse in 00:08:00
>>> 7474 7473 22773 30612 30612 30612 30612 30612 30612 30612 30612
>>> 30612 30612, (suppressed due to dampening)
>>> 203.13.132.35 from 203.13.132.35 (172.26.32.42)
>>> Origin IGP, localpref 100, valid, external
>>> Community: 7473:22015 7473:32265 7474:1403
>>> Dampinfo: penalty 1077, flapped 8 times in 00:48:32, reuse in 00:07:50
>>>
>>>
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>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>
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Received on Tue Aug 31 2010 - 08:13:08 ART