[lacnog] ANULAR SUSCRIPCION

Sab Jul 28 17:57:27 BRT 2012

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GRACIAS

2012/7/28 Christian O'Flaherty <christian.oflaherty en gmail.com>

> En la sesión de Lacnog en Mayo (Lacnic Quito) hubo una propuesta y una
> discusión en el micrófono sobre el uso de dampening.
> Yo sigo pensando que las experiencias no fueron buenas y por eso se
> dejó de usar...
> Me gustaría saber cuanto aporta nuestra región en ese "ruido" en la
> tabla global.
> Además, si nuestra región tuviera algún proveedor que tiene mucho
> route flap es mas facil trabajar con ese proveedor y resolverlo en
> lugar de proponer a todo el mundo que empiece a penalizar.
> Se podrá conseguir información sobre los ASs responsables?
>
> Christian
>
> On Thu, Jul 26, 2012 at 5:42 PM, Arturo Servin <aservin en lacnic.net> wrote:
> >
> > No se si muchos de los operadores en LAC usen Route Flap Damping, pero
> para
> > los que lo usen esto puede ser interesante.
> >
> > Slds
> > as
> >
> > Begin forwarded message:
> >
> > From: Rob Evans <rhe en nosc.ja.net>
> > Subject: [routing-wg] Route flap damping considered usable
> > Date: 26 July 2012 10:11:10 GMT-03:00
> > To: routing-wg en ripe.net
> >
> > All,
> >
> > Those of you that were in Ljubljana will have seen Randy Bush's
> presentation
> > 'Route Flap Damping Made Useful.'
> >
> > Based on the work behind this, Randy, Cristel Pelsser, Mirjam Kuehne and
> > myself have produced the following document which we'd like to publish
> as a
> > document of this working group.  Please have a look and discuss on this
> > list.
> >
> > I'd also like to remind you that we'll be meeting nine weeks from today
> in
> > Amsterdam at RIPE65.  I should be allowed out for this meeting, so if you
> > have any suggestions for what you'd like to see on the working group's
> > agenda, please send it to Joao and myself via <
> routing-wg-chairs en ripe.net>.
> >
> > Hope you're having a good summer!
> >
> > Rob
> >
> >
> > RIPE Routing Working Group
> > Recommendations on Route Flap Damping
> >
> > Introduction
> >
> > Route Flap Damping (RFD) [1] is a mechanism for BGP speaking routers
> > that penalises prefixes that exhibit a large number of updates
> > (‘flapping’), and suppresses a route when the accumulated penalty
> > exceeds a given threshold.  The penalty decays over time until it
> > reaches a lower threshold at which point the route is unsuppressed.
> > RFD is intended to improve the overall stability of the Internet
> > routing table and reduce the load on BGP speaking routers. In
> > ripe-378 [2] it was stated that due to the dynamics of BGP, especially
> > a phenomenon called ‘path hunting,’ the default configurations of
> > flap damping can do more harm than good as it may suppress a prefix
> > after it has only flapped a few times. Consequently RFD was deprecated
> > due to the problem of over damping (see [2] for more details).
> >
> > A small number of prefixes on the Internet continue to flap rapidly
> > and cause a disproportionate number of updates to BGP and load on
> > BGP speaking routers, this document uses experimental data gathered
> > from an operational environment to suggest changes to the RFD
> > parameters to suppress the prefixes that flap the most, while
> > minimising the suppression of other prefixes.
> >
> > This document suggests parameters which would make RFD usable and
> > is based around the work of Cristel Pelsser, Olaf Maennel, Pradosh
> > Mohapatra, Randy Bush, and Keyur Patel presented at PAM2011[3].
> >
> > History and Background
> >
> > In the early 1990s the accelerating growth in the number of prefixes
> > being announced to the Internet (often due to inadequate prefix
> > aggregation), the denser meshing through multiple inter-provider
> > paths, and increased instabilities started to cause significant
> > impact on the performance and efficiency of some Internet backbone
> > routers. Every time a routing prefix altered state because of a
> > single line-flap, the withdrawal was advertised to the whole
> > BGP-Speaking Zone (BSZ) and handled by every router that carried
> > the full Internet routing table.
> >
> > The load this processing placed on the control planes of routers
> > caused further instability as the routers were not able to process
> > other BGP updates or they dropped traffic transiting the device.
> > This could produce cyclic crashing behaviour.
> >
> > To overcome this situation RFD was developed in 1993 and has since
> > been integrated into most router BGP software implementations. RFD
> > is described in detail in RFC 2439[1].
> >
> > When RFD was first implemented in commercial routers, vendor
> > implementations had different default values and different
> > characteristics. As this inconsistency would result in different
> > rates of flap damping, and therefore introduce inconsistent path
> > selection and behavior that was hard to diagnose, the operator
> > community introduced a consistent set of recommendations for flap
> > damping parameters, so that ISPs deploying RFD would treat flapping
> > prefixes in the same way.
> >
> > This call for consistency resulted in the RIPE Routing Working Group
> > producing first ripe-178, then ripe-210, and finally the ripe-229
> > documents [2a].  The parameters documented in ripe-229 were considered,
> > at  time of publication in 2001, the best current practice. In 2006,
> > this was reviewed again and resulted in ripe-378 [2] which recommended
> > to disable RFD because it created more harm than good.
> >
> > Analysis
> >
> > In the work by Pelsser et al [3], it is shown that 3% of all prefixes
> > cause 36% of BGP updates, and just 0.01% of the prefixes cause 10%
> > of the BGP updates.  The aim is to only penalise those prefixes
> > with excessive numbers of updates.
> >
> > The default values used in current implementations of RFD apply a
> > penalty of 1000 each time a route flaps, and suppresses the prefix
> > when the penalty exceeds a figure in the region of 2000 (Cisco IOS)
> > or 3000 (Juniper JunOS).
> >
> > The table shows the percentage of prefixes above the suppress
> > threshold and the percentage reduction in BGP churn for various
> > values of suppress threshold.  The current default suppress value
> > of 2000 reduces BGP churn by 47%, but it suppressed 14% of the
> > prefixes at some point over the lifetime of the experiment.
> > Significantly larger values of suppress threshold such as 12000,
> > 15000 or 18000 still reduced BGP churn, but suppressed far fewer
> > prefixes which it is believed reduces the risk of penalising otherwise
> > well-behaved prefixes.
> >
> > Suppress % prefixes % reduction in BGP churn
> > Threshold suppressed compared with no damping
> > 2000 14 47
> > 4000 4.2 26
> > 6000 2.1 19
> > 12000 0.63 11.26
> > 15000 0.44 9.51
> > 18000 0.32 8.12
> >
> >
> > Recommendations
> >
> > In order to punish the biggest offenders - those prefixes that flap
> > the most – yet without punishing others, the RIPE Routing-WG
> > recommends vendors raise the maximum suppress threshold in router
> > implementations to 50,000 and operators configure a suppress threshold
> > value of at least 6,000.   The vendors might also change the default
> > suppress threshold to 6,000.  But this might surprise operators who
> > use the defult.
> >
> > This has a number of advantages:
> > • it is easy to implement
> > • it will reduce the churn compared to the situation we have
> > now where no RFD is applied
> > • it spares the smaller offenders.
> >
> > Changing the default suppress threshold could result in an increase
> > in forwarding table size or announcement rate for operators who use
> > RFD with the default settings.  This warrants further discussion.
> >
> > References
> > [1] Curtis Villamizar, Ravi Chandra, Ramesh Govindan
> > RFC2439: BGP Route-flap Damping (Proposed Standard)
> > <ftp://ftp.ietf.org/rfc/rfc2439.txt>
> > [2] Most recent RIPE Document
> > <ftp://ftp.ripe.net/ripe/docs/ripe-378.txt>
> >
> > [2a] Older RIPE Documents
> > <ftp://ftp.ripe.net/ripe/docs/ripe-178.txt>
> > <ftp://ftp.ripe.net/ripe/docs/ripe-210.txt>
> > <ftp://ftp.ripe.net/ripe/docs/ripe-229.txt>
> >
> > [3] Cristel Pelsser, Olaf Maennel, Pradosh Mohapatra, Randy Bush
> > and Keyur Patel. "Route Flap Damping Made Usable". PAM 2011, March
> > 2011.
> > <
> http://www.iij-ii.co.jp/en/lab/researchers/cristel/publications/Pelsser-RFD-PAM2011.pdf
> >
> >
> > [4] Zhouqing Mao, Ramesh Govindan, George Varghese, Randy Katz
> > Route-flap Damping Exacerbates Internet Routing Congerence SIGCOMM 2002
> > <http://www.eecs.umich.edu/~zmao/Papers/sig02.pdf>
> >
> > [5] Randy Bush, Tim Griffin, Zhouqing Mao Route-flap Damping: Harmful?
> > NANOG 26
> > <http://www.nanog.org/mtg-0210/ppt/flap.pdf>
> >
> > [6] Craig Labovitz, Abha Ahuja, Abhijit Bose, Farnam Jihanian
> > Delayed Internet Routing Convergence
> > SIGCOMM 2000
> > <
> http://www.acm.org/sigs/sigcomm/sigcomm2000/conf/paper/sigcomm2000-5-2.pdf
> >
> >
> >
> >
> > _______________________________________________
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> >
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