Network Working GroupInternet Engineering Task Force (IETF) C. PelsserInternet-DraftRequest for Comments: 7196 R. BushIntended status:Category: Standards Track Internet Initiative JapanExpires: April 14, 2014ISSN: 2070-1721 K. Patel Cisco Systems P. Mohapatra Cumulus Systems, Inc. O. Maennel Loughborough UniversityOctober 11, 2013April 2014 Making Route Flap Damping Usabledraft-ietf-idr-rfd-usable-04Abstract Route Flap Damping (RFD) was first proposed to reduce BGP churn in routers. Unfortunately, RFD was found to severely penalize sites for beingwell-connectedwell 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 andlimits,limits in order to reduce the high risks withRFD, with theRFD. The resultbeingis damping a non-trivial amount oflong termlong-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" 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.Status of This Memo ThisInternet-Draftissubmitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documentsan Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF).Note that other groups may also distribute working documents as Internet-Drafts. The listIt represents the consensus ofcurrent Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents validthe IETF community. It has received public review and has been approved fora maximumpublication 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 ofsix monthsthis document, any errata, and how to provide feedback on it may beupdated, replaced, or obsoleted by other documentsobtained atany time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 14, 2014.http://www.rfc-editor.org/info/rfc7196. Copyright Notice Copyright (c)20132014 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.Suggested Reading .Introduction . . . . . . . . . . . . . . . . . . . . .2 2. Introduction. . . 2 1.1. Suggested Reading . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language .2 3. RFD Parameters. . . . . . . . . . . . . . . . . . . 3 3. RFD Parameters . . . .3 4. Suppress Threshold Versus Churn. . . . . . . . . . . . . . .4 5. Maximum Penalty. . . . 3 4. Suppress Threshold versus Churn . . . . . . . . . . . . . . . 3 5. Maximum Penalty . . . .4 6. Recommendations. . . . . . . . . . . . . . . . . . . 4 6. Recommendations . . . .5 7. Security Considerations. . . . . . . . . . . . . . . . . . . 58. IANA7. Security Considerations . . . . . . . . . . . . . . . . . . .. .59.8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 510.9. References . . . . . . . . . . . . . . . . . . . . . . . . . 510.1.9.1. Normative References . . . . . . . . . . . . . . . . . . 510.2.9.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 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][RIPE178] and [RFC2439]) and subsequently implemented to reduce BGP churn in routers. Unfortunately, RFD was found to severely penalize sites for beingwell-connectedwell connected because topological richness amplifies the number of update messages exchanged, see[mao2002].[MAO2002]. Subsequently, many operators turned RFDoff,off; see[ripe378].[RIPE378]. Based on the measurements of[pelsser2011], [ripe580][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 andlimits, with thelimits. The resultbeingis damping of anon-trivialnon- trivial amount oflong termlong-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 arouter,router; see[huston2006][HUSTON2006] and[pelsser2011].[PELSSER2011]. For example, the measurements in[pelsser2011][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 provider and an Internet Exchange Point during aone weekone-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 anduse. It is not a panacea, noruse. 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 isit a deepreported in [RFD-SURVEY]. 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", andthorough approach"OPTIONAL" are toflap reduction.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 |10001,000 |10001,000 | | Re-Advertisement | No | 0 |10001,000 | | Attribute Change | No | 500 | 500 | | Suppress Threshold | Yes |20002,000 |30003,000 | | Half-Life(min)(min.) | Yes | 15 | 15 | | Reuse Threshold | Yes | 750 | 750 | | Max Suppress Time(min)(min.) | Yes | 60 | 60 |+-------------------------+----------+-------+---------++--------------------------+----------+-------+---------+ Note: Values without units specified are dimensionless constants. Table 1: Default RFDParamatersParameters of Juniper and CiscoTable 14. Suppress ThresholdVersusversus Churn By turning RFD back on with the values recommended in Section66, churn is reduced. Moreover, with these values, prefixes going through normal convergence are generally not damped.[pelsser2011][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.I.e.That is, far fewerwell- behavedwell-behaved prefixes are damped. Setting the suppress threshold to 12,000 leads to very few damped prefixes(1.7%(0.22% of the prefixes were damped with a threshold of2,000,12,000 in the experiments in[pelsser2011][PELSSER2011], yielding an average hourly update reduction of 11% compared to not usingRFD. +-----------------+-----------------+-------------+-----------------+RFD). +---------------+-------------+--------------+----------------------+ | Suppress | Damped | % of Table | Update Rate (one- | | Threshold |InstancesPrefixes | Damped |(onehour bins) |+-----------------+-----------------+-------------+-----------------++---------------+-------------+--------------+----------------------+ | 2,000 |4334243,342 | 13.16% | 53.11% | | 4,000 |1125311,253 | 3.42% | 74.16% | | 6,000 |43524,352 | 1.32% | 81.03% | | 8,000 |21042,104 | 0.64% | 84.85% | | 10,000 |12861,286 | 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% |+-----------------+-----------------+-------------+-----------------+ Damped Prefixes vs. Churn, from [pelsser2011]. Note overly- aggressive+---------------+-------------+--------------+----------------------+ Note: the current default Suppress Threshold (2,000) is overly agressive. Table22: Damped Prefixes vs. Churn, from [PELSSER2011] 5. Maximum Penalty It is important to understand that the parameters shown in Table1,1 and the implementation's samplingrate,rate impose an upper bound on the penalty value, which we can call the 'computed maximum penalty'. In addition, BGP implementations have an internalconstantconstant, which we will call the 'maximumpenalty' whichpenalty', and the current computed penalty may notexceed.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 BGPimplementations including,implementations, including the examples in Table 1, SHOULD NOT change their default values. Minimum Suppress Threshold: Operatorswishingthat want dampingwhichthat is much less destructive thancurrent,the current damping, but still somewhataggressiveaggressive, 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 operatorcouldcan see the results of a particular configuration without actually damping any prefixes. This will allow forfine tuningfine-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 thefalse flapfalse-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.10.9. References10.1.9.1. 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.[mao2002] Mao, Z. M., Govidan, R., Varghese, G., Katz, R., "Route Flap Damping Excacerbates 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., Patel, K., "Route Flap Damping Made Usable", Passive[RIPE378] Smith, P. andActive Measurement (PAM), March 2011, <http://pam2011.gatech.edu/papers/pam2011--Pelsser.pdf>. [ripe378] Panigl,P.Smith, P.,Panigl, "RIPE Routing Working Group Recommendations On Route-flap Damping", RIPE 378, May 2006, <http://www.ripe.net/ripe/docs/ripe-378>.10.2.9.2. Informative References[I-D.shishio-grow-isp-rfd-implement-survey][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",draft- shishio-grow-isp-rfd-implement-survey-05 (workWork inprogress),Progress, June 2012.[huston2006] Huston, G., "BGP Extreme Routing Noise", RIPE 52 , 2006, <http://meetings.ripe.net/ripe-52/presentations/ripe52 -plenary-bgp-review.pdf>. [ripe178][RIPE178] Barber, T., Doran, S., Karrenberg, D., Panigl, C., and J. Schmitz,J.,"RIPE Routing-WG Recommendation for Coordinated Route-flap Damping Parameters",2001,RIPE 178, February 1998, <http://www.ripe.net/ripe/docs/ripe-178>.[ripe580] Pelsser, C.,[RIPE580] Bush, R., Pelsser, C., Kuhne, M., Maennel, O.,Patel, K.,Mohapatra, P.,Kuhne, M.,Patel, K., and R. Evans,R.,"RIPERouting-WGRouting Working Group Recommendation forRoute-flapRoute Flap Damping", RIPE 580, January 2013, <http://www.ripe.net/ripe/docs/ripe-580>. 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 Cumulus Systems, Inc. 2672 Bayshore Parkway, Suite 515 Mountain View, CA 94043 US Email: pmohapat@cumulusnetworks.com Olaf Maennel Loughborough University Department of Computer Science - N.2.03 Loughborough UK Phone: +44 115 714 0042 Email: o@maennel.net