Coming into this discussion a little late, it's important to
distinguish between flaps and flapping. Flaps are single events: the
cycle of announce/withdraw/announce over a short period of time.
Various timing parameters influence the point at which flaps become
flapping. Some providers have additional conditional elements --
they are less tolerant of flapping on long prefixes -- they would put
up with more flapping on a /19 than on a /24.
As an aside, both Cisco and IETF documents are inconsistent about
calling the countermeasure damping or dampening. In control system
theory, the correct term is damping.
As a gardener, however, dampening is a good thing to do to seedlings,
making them moist and green. A damped seedling has gone limp and is
on its way to the Great Compost Pile in the Sky.
>And it's all tied to time as well, so just don't go down/up within a very
>short period (just go down, do your work, then back up). If you know you're
>going to take a BGP announcing router offline and don't want there to be any
>possibility of things bouncing while you're working, shutdown your BGP
>neighbors so you won't be announcing and then withdrawing them. So long as
>I've done that, I've never had dampening problems. When I'm all done, I
>just no shutdown the BGP neighbors and we've got no dampening penalties.
>Before learning about the BGP neighbor shutdown command, I was getting
>dampened a bit as the serial line would sometimes bounce when first coming
>up and the BGP neighbors were already exchanging routes. Also important is
>to kill your iBGP neighbors statements as well (shutdown command), as you
>don't want them to be flapping any routes that originate from the router
>you're working on. An example of the command:
>router bgp 18506
> neighbor 63.123.123.166 shutdown
>
>Worst case, when I was first installing BGP and tweaking with memory and how
>many routes we could hold (and crashing and losing our BGP sessions), I
>think I probably flapped 10 times and got dampened for 2 hours from some
>ISPs. Of course, we were working after hours so no big deal, but now that I
>know better I wouldn't announce any routes until I knew everything else was
>stable.
>
>BGP looking glasses are very useful to see if you're getting dampened ;-)
>telnet://route-views.oregon-ix.net
>telnet://route-server.cerf.net
>
>--
>Jason Roysdon, CCNP+Security/CCDP, MCSE, CNA, Network+, A+
>List email: [EMAIL PROTECTED]
>Homepage: http://jason.artoo.net/
>
>
>
>""Priscilla Oppenheimer"" wrote in message
>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
>> It doesn't answer the question. It says there's a penalty for each flap.
>Is
>> there a penalty for
>>
>> 1. each time a route goes down
>> or
>> 2. each time a route goes down and back up
>>
>> The answer is probably number 2, as the orignal poster thought also,
since
>> just going down isn't really "flapping."
>>
>> Priscilla
>>
>> At 05:18 AM 4/19/01, Andy Prima wrote:
>> >Please let me quote from sitamoth.com:
>> >
>> >Route dampening is a BGP feature designed to minimize the propagation of
>> >flapping routes across an internetwork. A route is considered to be
>flapping
>> >when it is repeatedly available, then unavailable, then available then
>> >unavailable..and so on.
>> >A route that is flapping receives a penalty of 1000 for each flap. When
>the
>> >accumulated pelanlty reaches a configurable limit, BGP surpresses
>> >advertisement of the route EVEN if the route is UP.
>> >The accumulated penalty is decremented by the half-life time. When the
>> >accumulated penalty is less than the reuse limit, the route is
advertised
>> >again (if it is still UP).
>> >
>> >
>> >Hope this can help :)
>> >
>> >Andy
>> >
>> >-----Original Message-----
>> >From: Stephen Skinner [mailto:[EMAIL PROTECTED]]
>> >Sent: Thursday, April 19, 2001 3:53 PM
>> >To: [EMAIL PROTECTED]
>> >Subject: Re: BGP Dampening, What is a flap? [7:1128]
>> >
>> >
>> >I always thought of a "Flap" as a generic term ....meaning when a
>> >route/interface/serial-line goes full-circle.....regardless of protocol
> > >i use the term interchangeably with OSPF,PpP,LEASED lines,BGP,ISDN
>> >
>> >from:- working----down----initialising----up
>> >
>> >i have always treated the "whole" as one flap?????
>> >
>> >Am i going mad.....
>> >
>> >Cheers
>> >
>> >steve
>> >
>> >"my mum always said ....it`s only an exam.......PAH...what the heck do
>she
>> >know"
>> >
>> >
>> > >From: "Priscilla Oppenheimer"
>> > >Reply-To: "Priscilla Oppenheimer"
>> > >To: [EMAIL PROTECTED]
>> > >Subject: Re: BGP Dampening, What is a flap? [7:1128]
>> > >Date: Wed, 18 Apr 2001 18:09:50 -0400
>> > >
>> > >I think from BGP's point of view a flap is a withdrawal and
>announcement
>> of
>> > >a routing prefix. Howard Berkowitz will know for sure. Did you check
>his
>> > >BGP papers at http://www.certificationzone.com. Also there's a good
>paper
>> > >here:
>> > >
>> > >http://www.ripe.net/ripe/docs/ripe-178.html
>> > >
>> > >Cisco often uses the word "flapping" in a generic sense for a route or
>> > >interface going up and down repeatedly. That could be cause for some
>> > >confusion. In your class, you might want to be clear about whether you
>are
>> > >using the term generically or with reference to parameters to route
>> > >dampening commands.
>> > >
>> > >Good luck. Let us know what you find out for sure! Thanks.
>> > >
>> > >Priscilla
>> > >
>> > >At 03:35 PM 4/18/01, Tom Pruneau wrote:
>> > > >Greetings All
>> > > >
>> > > >I am in the process of writing a BGP class, at present I am
>specifically
>> > > >working on a section covering dampening.
>> > > >
>> > > >My question is "what is a flap"
>> > > >
>> > > >The two possible answers are:
>> > > >
>> > > >
>> > > >Answer one
>> > > >A flap is whenever path information changes for a route. By this
>> > >definition
>> > > >if a route goes away, that would be a flap. When the route comes
>back,
>> > >that
>> > > >would be another flap.
>> > > >So a route going away then coming back would be 2 flaps.
>> > > >
>> > > >
>> > > >Answer two
>> > > >A flap is a route transition from up to down back to up. So a route
>> going
>> > > >away then coming back would count as one flap.
>> > > >
>> > > >
>> > > >
>> > > >I am mucking with this in my lab and the lab would seem to indicate
>that
>> > > >answer two is the correct one, but when I read the Sam Halabi
>copyright
>> > > >1997 internet routing architectures book, page 440 and 441 it says
>the
>> > > >answer is Answer one.
>> > > >
>> > > >I am at best confused
>> > > >
>> > > >Any help?
>> > > >Tom Pruneau
>> > > >Trainer Network Operations
>> > > >
>> > > >GENUITY
>> > > >3 Van de Graff Drive Burlington Ma. 01803
>> > > >24 Hr. Network Operations Center 800-436-8489
>> > > >If you need to get a hold of me my hours are 8AM-4PM ET Mon-Fri
>> > > >
>> > >
>> >
>>
>>---------------------------------------------------------------------------
>> > > >This email is composed of 82% post consumer recycled data bits
>> > >
>> >
>>
>>---------------------------------------------------------------------------
>> > > >
>> > > >"Once in a while you get shown the light
>> > > >in the strangest of places if you look at it right"
>> > > >FAQ, list archives, and subscription info:
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>> > >
>> > >________________________
>> > >
>> > >Priscilla Oppenheimer
>> > >http://www.priscilla.com
>> > >FAQ, list archives, and subscription info:
>> > >http://www.groupstudy.com/list/cisco.html
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>> >
>>
>_________________________________________________________________________
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>> ________________________
>>
>> Priscilla Oppenheimer
>> http://www.priscilla.com
>> FAQ, list archives, and subscription info:
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