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and derivative works of it may not be created, and it may not be
published except as an Internet-Draft.
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This Internet-Draft will expire on June 24, 2012.
Copyright Notice
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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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