Re: BGP Dampening?

Right now I have a scenario where dampening is probably going to be used to
help keep badly flapping links to stay suppressed in one of my networks.

Love this stuff.

Hey every command has a purpose. Find it.

On Wed, Jul 22, 2009 at 10:34 PM, Ramanpreet Singh <sikandar.raman_at_gmail.com
> wrote:

> This is the explanation of BGP dampening from BGP
> command-reference handbook
>
> A route flap occurs when a prefix transitions from the up to the down
> state.
> When the prefix goes from up to down, BGP must send a WITHDRAWN message.
> When the prefix goes from down to up, BGP sends an UPDATE message. If the
> prefix is constantly flapping, this can cause high CPU utilization while
> the
> BGP routes are converging. Additionally, if you are redistributing BGP into
> your IGP, the flapping route can cause instability in the IGP. Dampening is
> a method to control the effect of a flapping route.
>
> Assume that BGP route dampening has been applied to a particular route.
> Remember that a route flap is when a prefix goes from the up to the down
> state. When a route flaps, a penalty of 1000 is applied to the route. This
> is a fixed parameter that cannot be changed. At time t1, the flapping route
> incurs a penalty of 1000. Because the penalty is less than the suppress
> limit, which has been configured to be 1500, the flapping route is not
> dampened. Because the route has not been dampened, BGP sends a WITHDRAWN
> message when the route goes from up to down and then an UPDATE message when
> the route goes from down to up. When route dampening is enabled, BGP must
> maintain a history of flapping routes. The penalty associated with the
> route
> decreases over time. The rate of decrease in the penalty is a function of
> the half-life. The half-life is the amount of time for the penalty to
> decrease to half of its current value. If the half-life is 15 minutes, the
> penalty decreases to 500 in 7.5 minutes. At time t2, the penalty decreases
> to 600, and another route flap occurs. The route is again penalized, with
> an
> additional value of 1000 added to the current value of the penalty. The
> total penalty associated with the route is now 1600. When the total penalty
> of a route becomes greater than the suppress limit, the route is dampened.
> A
> dampened route means that BGP no longer sends UPDATE messages when the
> prefix goes from the down to the up state. The flapping prefix remains in
> the WITHDRAWN state. The route remains in the WITHDRAWN state until its
> penalty decreases below the reuse limit. When the penalty decreases below
> the reuse limit, BGP sends an UPDATE message for the route. Routes learned
> via IBGP are not dampened
>
> On Wed, Jul 22, 2009 at 9:14 PM, Joe Astorino <jastorino_at_ipexpert.com
> >wrote:
>
> > I don't have it in front of me because I am out of town, but the BGP
> > command-reference handbook from Cisco is pretty good. It gives pretty
> > straight forward examples on just about everything. I have it at home
> and
> > now I am curious as to what it says on this topic.
> >
> > On Wed, Jul 22, 2009 at 9:40 PM, Tony Varriale
> > <tvarriale_at_flamboyaninc.com>wrote:
> >
> > > The Halabi book isn't really the bible anymore. In fact, it would be
> > very
> > > difficult for me to recommend it to anyone.
> > >
> > > tv
> > >
> > > -----Original Message-----
> > > From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf
> Of
> > > Gary
> > > Duncanson
> > > Sent: Wednesday, July 22, 2009 5:57 PM
> > > To: Joe Astorino
> > > Cc: Ramanpreet Singh; ccielab_at_groupstudy.com
> > > Subject: Re: BGP Dampening?
> > >
> > > This makes sense now.
> > >
> > > There's nothing in Halibi the 'bible' on BGP so there you go. I just
> > > checked
> > >
> > > at least in the index for BGP dampening but it must be covered in the
> > > fundamentals of the book.
> > >
> > > I suppose decay time is 'half life' in which case check out page 293 of
> > the
> > > book. Semantics :)
> > >
> > > Granualar stuff this! DocCD all the way.
> > > ----- Original Message -----
> > > From: "Joe Astorino" <jastorino_at_ipexpert.com>
> > > To: "Ramanpreet Singh" <sikandar.raman_at_gmail.com>
> > > Cc: "CCIE Groupstudy" <ccielab_at_groupstudy.com>
> > > Sent: Wednesday, July 22, 2009 11:37 PM
> > > Subject: Re: BGP Dampening?
> > >
> > >
> > > > The half life time is the time in which the penalty will be half of
> > what
> > > > it
> > > > is currently
> > > > The Max suppress penaltly is just the max time the route can be
> > > > suppressed.
> > > >
> > > > Check out the routing config guide under BGP for a much more in depth
> > > > explanation
> > > >
> > > > On Wed, Jul 22, 2009 at 5:57 PM, Ramanpreet Singh
> > > > <sikandar.raman_at_gmail.com>wrote:
> > > >
> > > >> Can anyone help me understanding Decay time and Max suppress
> penalty?
> > > >>
> > > >> I am familiar with other parameters but I am not able to understand
> > how
> > > >> Decay time and Max suppress penalty is calculated. Doc CD only
> > explains
> > > >> the
> > > >> configurable parameters but not decay time and Max suppress penalty.
> > > >>
> > > >> Thanks!
> > > >>
> > > >>
> > > >> Blogs and organic groups at http://www.ccie.net
> > > >>
> > > >>
> > _______________________________________________________________________
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> > > >>
> > > >>
> > > >>
> > > >>
> > > >>
> > > >>
> > > >
> > > >
> > > > --
> > > > Regards,
> > > >
> > > > Joe Astorino - CCIE #24347 R&S
> > > > Technical Instructor - IPexpert, Inc.
> > > > Cell: +1.586.212.6107
> > > > Fax: +1.810.454.0130
> > > > Mailto: jastorino_at_ipexpert.com
> > > >
> > > >
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> > > >
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> > >
> > >
> >
> >
> > --
> > Regards,
> >
> > Joe Astorino - CCIE #24347 R&S
> > Technical Instructor - IPexpert, Inc.
> > Cell: +1.586.212.6107
> > Fax: +1.810.454.0130
> > Mailto: jastorino_at_ipexpert.com
> >
> >
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> >
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>
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Received on Thu Jul 23 2009 - 00:27:52 ART