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rfc:rfc7196

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.

Pelsser, et al. Standards Track [Page 1] RFC 7196 Making Route Flap Damping Usable May 2014

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
 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
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 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

Pelsser, et al. Standards Track [Page 2] RFC 7196 Making Route Flap Damping Usable May 2014

 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

Pelsser, et al. Standards Track [Page 3] RFC 7196 Making Route Flap Damping Usable May 2014

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'.

Pelsser, et al. Standards Track [Page 4] RFC 7196 Making Route Flap Damping Usable May 2014

 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.

Pelsser, et al. Standards Track [Page 5] RFC 7196 Making Route Flap Damping Usable May 2014

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>.

Pelsser, et al. Standards Track [Page 6] RFC 7196 Making Route Flap Damping Usable May 2014

 [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>.

Pelsser, et al. Standards Track [Page 7] RFC 7196 Making Route Flap Damping Usable May 2014

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

Pelsser, et al. Standards Track [Page 8]

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