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Network Working Group                                         C. Pelsser
Internet-Draft                                                   R. Bush
Intended status: Standards Track               Internet Initiative Japan
Expires: June 24, 2012                                          K. Patel
                                                            P. Mohapatra
                                                           Cisco Systems
                                                               O. Maenel
                                                 Loughborough University
                                                       December 22, 2011


                    Making Route Flap Damping Usable
                        draft-ymbk-rfd-usable-02

Abstract

   Route Flap Damping (RFD) was first proposed to reduce BGP churn in
   routers.  Unfortunately, RFD was found to severely penalize sites for
   being well-connected because topological richness amplifies the
   number of update messages exchanged.  Many operators have turned RFD
   off.  Based on experimental measurement, this document recommends
   adjusting a few RFD algorithmic constants and limits, to reduce the
   high risks with RFD, with the result being damping a non-trivial
   amount of long term churn without penalizing well-behaved prefixes'
   normal convergence process.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, and it may not be
   published except as an Internet-Draft.

   Internet-Drafts are working documents of the Internet Engineering
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."



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   This Internet-Draft will expire on June 24, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



































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Table of Contents

   1.  Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  RFD Parameters  . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Suppress Threshold Versus Churn . . . . . . . . . . . . . . . . 5
   5.  Maximum Penalty . . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     10.1.  Normative References . . . . . . . . . . . . . . . . . . . 7
     10.2.  Informative References . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8




































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1.  Suggested Reading

   It is assumed that the reader understands BGP, [RFC4271] and Route
   Flap Damping, [RFC2439].  This work is based on the measurements in
   the paper [pelsser2011].  A survey of Japanese operators' use of RFD
   and their desires is reported in
   [I-D.shishio-grow-isp-rfd-implement-survey].


2.  Introduction

   Route Flap Damping (RFD) was first proposed (see [ripe178] and
   [RFC2439]) and subsequently implemented to reduce BGP churn in
   routers.  Unfortunately, RFD was found to severely penalize sites for
   being well-connected because topological richness amplifies the
   number of update messages exchanged, see [mao2002].  Subsequently,
   many operators turned RFD off, see [ripe378].  Based on experimental
   measurements, this document recommends adjusting a few RFD
   algorithmic constants and limits, with the result being damping of a
   non-trivial amount of long term churn without penalizing well-behaved
   prefixes' normal convergence process.

   Very few prefixes are responsible for a large amount of the BGP
   messages received by a router, see [huston2006] and [pelsser2011].
   For example, the measurements in [pelsser2011] showed that only 3% of
   the prefixes were responsible for 36% percent of the BGP messages at
   a router with real feeds from a Tier-1 and an Internet Exchange Point
   during a one week experiment.  Only these very frequently flapping
   prefixes should be damped.  The values recommended in Section 6
   achieve this.  Thus, RFD can be enabled, and some churn reduced.

   The goal is to, with absolutely minimal change, ameliorate the danger
   of current RFD implementations and use.  It is not a panacea, nor is
   it a deep and thorough approach to flap reduction.


3.  RFD Parameters

   The following RFD parameters are common to all implementations.  Some
   may be tuned by the operator, some not.











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         +-------------------------+----------+-------+---------+
         | Parameter               | Tunable? | Cisco | Juniper |
         +-------------------------+----------+-------+---------+
         | Withdrawal              | No       |  1000 |    1000 |
         | Re-Advertisement        | No       |     0 |    1000 |
         | Attribute Change        | No       |   500 |     500 |
         | Suppress Threshold      | Yes      |  2000 |    3000 |
         | Half-Life (min)         | Yes      |    15 |      15 |
         | Reuse Threshold         | Yes      |   750 |     750 |
         | Max Suppress Time (min) | Yes      |    60 |      60 |
         +-------------------------+----------+-------+---------+

                Default RFD Paramaters of Juniper and Cisco

                                  Table 1


4.  Suppress Threshold Versus Churn

   By turning RFD back on with the values recommended in Section 6 churn
   is reduced.  Moreover, with these values, prefixes going through
   normal convergence are generally not damped.

   [pelsser2011] estimates that, with a suppress threshold of 6,000, the
   BGP update rate is reduced by 19% compared to a situation without RFD
   enabled.  With this 6,000 suppress threshold, 90% fewer prefixes are
   damped compared to use of a 2,000 threshold.  I.e. far fewer well-
   behaved prefixes are damped.

   Setting the suppress threshold to 12,000 leads to very few damped
   prefixes (1.7% of the prefixes damped with a threshold of 2,000, in
   the experiments in [pelsser2011] yielding an average hourly update
   reduction of 11% compared to not using RFD.


















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   +---------------+--------------+-------------+----------------------+
   |      Suppress |       Damped |  % of Table |     Update Rate (one |
   |     Threshold |    Instances |      Damped |           hour bins) |
   +---------------+--------------+-------------+----------------------+
   |         2,000 |        43342 |      13.16% |               53.11% |
   |         4,000 |        11253 |       3.42% |               74.16% |
   |         6,000 |         4352 |       1.32% |               81.03% |
   |         8,000 |         2104 |       0.64% |               84.85% |
   |        10,000 |         1286 |       0.39% |               87.12% |
   |        12,000 |          720 |       0.22% |               88.74% |
   |        14,000 |          504 |       0.15% |               89.97% |
   |        16,000 |          353 |       0.11% |               91.01% |
   |        18,000 |          311 |       0.09% |               91.88% |
   |        20,000 |          261 |       0.08% |               92.69% |
   +---------------+--------------+-------------+----------------------+

               Damped Prefixes vs. Churn, from [pelsser2011]

         Note overly-aggressive current default Suppress Threshold

                                  Table 2


5.  Maximum Penalty

   It is important to understand that the parameters shown in Table 1,
   and the implementation's sampling rate, impose an upper bound on the
   penalty value, which we can call the 'computed maximum penalty'.

   In addition, BGP implementations have an internal constant which we
   will call the 'maximum penalty' which the current computed penalty
   may not exceed.


6.  Recommendations

   The following changes are recommended:

   Router Maximum Penalty:  The internal constant for the maximum
      penalty value MUST be raised to at least 50,000.

   Default Configurable Parameters:  In order not to break existing
      operational configurations, BGP implementations SHOULD NOT change
      the default values in Table 1.







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   Minimum Suppress Threshold:  Operators wishing damping which is much
      less destructive than current, but still somewhat aggressive
      SHOULD configure the Suppress Threshold to no less than 6,000.

   Conservative Suppress Threshold:  Conservative operators SHOULD
      configure the Suppress Threshold to no less than 12,000.

   Calculate But Do Not Damp:  Implementations MAY have a test mode
      where the operator could see the results of a particular
      configuration without actually damping any prefixes.  This will
      allow for fine tuning of parameters without losing reachability.


7.  Security Considerations

   It is well known that an attacker can generate false flapping to
   cause a victim's prefix(es) to be damped.

   As the recommendations merely change parameters to more conservative
   values, there should be no increase in risk.

   In fact, the parameter change to more conservative values should
   slightly mitigate the false flap attack.


8.  IANA Considerations

   This document has no IANA Considerations.


9.  Acknowledgments

   Nate Kushman initiated this work some years ago.  Ron Bonica, Seiichi
   Kawamura, and Erik Muller contributed useful suggestions.


10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2439]  Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
              Flap Damping", RFC 2439, November 1998.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.



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   [mao2002]  Mao, Z. M., Govidan, R., Varghese, G., and Katz, R.,
              "Route Flap Damping Excacerbates Internet Routing
              Convergence", In Proceedings of SIGCOMM , August 2002, <ht
              tp://www.acm.org/sigcomm/sigcomm2002/papers/
              routedampening.pdf>.

   [pelsser2011]
              Pelsser, C., Maennel, O., Mohapatra, P., Bush, R., and
              Patel, K., "Route Flap Damping Made Usable", Passive and
              Active Measurement (PAM), March 2011,
              <http://archive.psg.com/110103.pam-rfd.pdf>.

   [ripe378]  Panigl, P. and Smith, P., "RIPE Routing Working Group
              Recommendations On Route-flap Damping", 2006,
              <http://www.ripe.net/ripe/docs/ripe-378>.

10.2.  Informative References

   [I-D.shishio-grow-isp-rfd-implement-survey]
              Tsuchiya, S., Kawamura, S., Bush, R., and C. Pelsser,
              "Route Flap Damping Deployment Status Survey",
              draft-shishio-grow-isp-rfd-implement-survey-02 (work in
              progress), June 2011.

   [huston2006]
              Huston, G., "BGP Extreme Routing Noise", RIPE 52 , 2006, <
              http://meetings.ripe.net/ripe-52/presentations/
              ripe52-plenary-bgp-review.pdf>.

   [ripe178]  Barber, T., Doran, S., Karrenberg, D., Panigl, C., and
              Schmitz, J., "RIPE Routing-WG Recommendation for
              Coordinated Route-flap Damping Parameters", 2001,
              <http://www.ripe.net/ripe/docs/ripe-178>.


Authors' Addresses

   Cristel Pelsser
   Internet Initiative Japan
   Jinbocho Mitsui Buiding, 1-105
   Kanda-Jinbocho, Chiyoda-ku, Tokyo  101-0051
   JP

   Phone: +81 3 5205 6464
   Email: cristel@iij.ad.jp






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   Randy Bush
   Internet Initiative Japan
   5147 Crystal Springs
   Bainbridge Island, Washington  98110
   US

   Phone: +1 206 780 0431 x1
   Email: randy@psg.com


   Keyur Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   US

   Email: keyupate@cisco.com


   Pradosh Mohapatra
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   US

   Email: pmohapat@cisco.com


   Olaf Maennel
   Loughborough University
   Department of Computer Science - N.2.03
   Loughborough
   UK

   Phone: +44 115 714 0042
   Email: o@maennel.net















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