





Internet Engineering Task Force (IETF)                        C. Pelsser
Request for Comments: 7196                                       R. Bush
Category: Standards Track                      Internet Initiative Japan
ISSN: 2070-1721                                                 K. Patel
                                                           Cisco Systems
                                                            P. Mohapatra
                                                        Sproute Networks
                                                              O. Maennel
                                                 Loughborough University
                                                                May 2014


                    Making Route Flap Damping Usable

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 in order to
   reduce the high risks with RFD.  The result is damping a non-trivial
   amount of long-term churn without penalizing well-behaved prefixes'
   normal convergence process.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7196.












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Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Suggested Reading . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  RFD Parameters  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Suppress Threshold versus Churn . . . . . . . . . . . . . . .   4
   5.  Maximum Penalty . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6

1.  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 the
   measurements of [PELSSER2011], [RIPE580] now recommends that RFD is
   usable with some changes to the parameters.  Based on the same
   measurements, this document recommends adjusting a few RFD
   algorithmic constants and limits.  The result is 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



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   the prefixes were responsible for 36% percent of the BGP messages at
   a router with real feeds from a Tier-1 provider 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.

1.1.  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 [RFD-SURVEY].

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
   be interpreted as described in RFC 2119 [RFC2119] only when they
   appear in all upper case.  They may also appear in lower or mixed
   case as English words, without normative meaning.

3.  RFD Parameters

   The following RFD parameters are common to all implementations.  Some
   may be tuned by the operator, some not.  There is currently no
   consensus on a single set of default values.

         +--------------------------+----------+-------+---------+
         | Parameter                | Tunable? | Cisco | Juniper |
         +--------------------------+----------+-------+---------+
         | Withdrawal               | No       | 1,000 |   1,000 |
         | Re-Advertisement         | No       |     0 |   1,000 |
         | Attribute Change         | No       |   500 |     500 |
         | Suppress Threshold       | Yes      | 2,000 |   3,000 |
         | Half-Life (min.)         | Yes      |    15 |      15 |
         | Reuse Threshold          | Yes      |   750 |     750 |
         | Max Suppress Time (min.) | Yes      |    60 |      60 |
         +--------------------------+----------+-------+---------+

     Note: Values without units specified are dimensionless constants.

           Table 1: Default RFD Parameters of Juniper and Cisco




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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.  [PELSSER2011] studies the number of prefixes damped over a
   week between September 29, 2010 and October 6, 2010.  With this 6,000
   suppress threshold, 90% fewer prefixes are damped compared to use of
   a 2,000 threshold.  That is, far fewer well-behaved prefixes are
   damped.

   Setting the suppress threshold to 12,000 leads to very few damped
   prefixes (0.22% of the prefixes were damped with a threshold of
   12,000 in the experiments in [PELSSER2011], yielding an average
   hourly update reduction of 11% compared to not using RFD).

   +---------------+-------------+--------------+----------------------+
   |      Suppress |      Damped |   % of Table |    Update Rate (one- |
   |     Threshold |    Prefixes |       Damped |           hour bins) |
   +---------------+-------------+--------------+----------------------+
   |         2,000 |      43,342 |       13.16% |               53.11% |
   |         4,000 |      11,253 |        3.42% |               74.16% |
   |         6,000 |       4,352 |        1.32% |               81.03% |
   |         8,000 |       2,104 |        0.64% |               84.85% |
   |        10,000 |       1,286 |        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% |
   +---------------+-------------+--------------+----------------------+

      Note: the current default Suppress Threshold (2,000) is overly
                                agressive.

          Table 2: Damped Prefixes vs. Churn, from [PELSSER2011]

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'.






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

6.  Recommendations

   Use of the following values is 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, existing BGP implementations,
      including the examples in Table 1, SHOULD NOT change their default
      values.

   Minimum Suppress Threshold:  Operators that want damping that is much
      less destructive than the current damping, 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 can 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.  Acknowledgments

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








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9.  References

9.1.  Normative References

   [MAO2002]  Mao, Z., Govidan, R., Varghese, G., and R. Katz, "Route
              Flap Damping Exacerbates Internet Routing Convergence", In
              Proceedings of SIGCOMM, August 2002,
              <http://conferences.sigcomm.org/sigcomm/2002/papers/
              routedampening.pdf>.

   [PELSSER2011]
              Pelsser, C., Maennel, O., Mohapatra, P., Bush, R., and K.
              Patel, "Route Flap Damping Made Usable", PAM 2011: Passive
              and Active Measurement Conference, March 2011,
              <http://pam2011.gatech.edu/papers/pam2011--Pelsser.pdf>.

   [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.

   [RIPE378]  Smith, P. and P. Panigl, "RIPE Routing Working Group
              Recommendations On Route-flap Damping", RIPE 378, May
              2006, <http://www.ripe.net/ripe/docs/ripe-378>.

9.2.  Informative References

   [HUSTON2006]
              Huston, G., "2005 - A BGP Year in Review", RIPE 52, 2006,
              <http://meetings.ripe.net/ripe-52/presentations/
              ripe52-plenary-bgp-review.pdf>.

   [RFD-SURVEY]
              Tsuchiya, S., Kawamura, S., Bush, R., and C. Pelsser,
              "Route Flap Damping Deployment Status Survey", Work in
              Progress, June 2012.

   [RIPE178]  Barber, T., Doran, S., Karrenberg, D., Panigl, C., and J.
              Schmitz, "RIPE Routing-WG Recommendation for Coordinated
              Route-flap Damping Parameters", RIPE 178, February 1998,
              <http://www.ripe.net/ripe/docs/ripe-178>.






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   [RIPE580]  Bush, R., Pelsser, C., Kuhne, M., Maennel, O., Mohapatra,
              P., Patel, K., and R. Evans, "RIPE Routing Working Group
              Recommendation for Route Flap Damping", RIPE 580, January
              2013, <http://www.ripe.net/ripe/docs/ripe-580>.















































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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


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

   EMail: randy@psg.com


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

   EMail: keyupate@cisco.com


   Pradosh Mohapatra
   Sproute Networks
   41529 Higgins Way
   Fremont, CA  94539
   US

   EMail: mpradosh@yahoo.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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