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"
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> > >
> > >________________________
> > >
> > >Priscilla Oppenheimer
> > >http://www.priscilla.com
> > >FAQ, list archives, and subscription info:
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>
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
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