Network Working Group C. Pelsser
Internet-Draft R. Bush
Intended status: Standards Track IIJ
Expires: September 8, 2011 K. Patel
P. Mohapatra
Cisco Systems
O. Maenel
Loughborough University
March 7, 2011
Making Route Flap Damping Usable
draft-ymbk-rfd-usable-00
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. 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
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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and derivative works of it may not be created, and it may not be
published except as an Internet-Draft.
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This Internet-Draft will expire on September 8, 2011.
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
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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. Suppress Threshold Versus Churn . . . . . . . . . . . . . . . . 4
4. RFD Parameters . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Maximum Penalty . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . . 7
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].
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]. 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, [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. 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 6K suppress threshold, 90% fewer prefixes are
damped compared to use of a 2K threshold. I.e. far fewer well-
behaved prefixes are damped.
Setting the suppress threshold to 12K leads to very few damped
prefixes (1.7% of the prefixes damped with a threshold of 2K, in the
experiments in [pelsser2011] yielding an average hourly update
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reduction of 11% compared to not using RFD.
+--------------------+------------------+---------------------------+
| Suppress Threshold | Damped Instances | Update Rate (one hour |
| | | bins) |
+--------------------+------------------+---------------------------+
| 2k | 43342 | 53.11% |
| 4k | 11253 | 74.16% |
| 6k | 4352 | 81.03% |
| 8k | 2104 | 84.85% |
| 10k | 1286 | 87.12% |
| 12k | 720 | 88.74% |
| 14k | 504 | 89.97% |
| 16k | 353 | 91.01% |
| 18k | 311 | 91.88% |
| 20k | 261 | 92.69% |
+--------------------+------------------+---------------------------+
Damped Prefixes Versus Churn
Table 1
4. RFD Parameters
The following RFD parameters are common to all implementations. Some
may be adjusted by the operator, some not.
+-------------------------+----------+-------+---------+
| 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 |
+-------------------------+----------+-------+---------+
RFD Paramaters of Juniper and Cisco
Table 2
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5. Maximum Penalty
It is important to understand that the parameters shown in Table 2,
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 2.
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.
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8. IANA Considerations
This document has no IANA Considerations.
9. Acknowledgments
Nate Kushman initiated this work some years ago. 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.
[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
[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
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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, Inc.
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, Inc.
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
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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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