Case Studies on Intra-Domain Routing Instability

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29 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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1

Case Studies on Intra
-
Domain
Routing Instability

Zhang Shu


Communications Research Laboratory, Japan


To be renamed to National Institute of Information and
Communications Technology)


APAN17


Engineering Session

1/30/2004, Hawaii

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Overview


What is routing instability?


Methodology of the measurement


Case study 1: WIDE Internet


Case study 2: APAN Tokyo
-
XP


Conclusion and future work

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Routing Instability


Routing instability


Also called route flaps


Unexpected topology change


Bad influence


Packet loss


Increased router load


Wasted bandwidth


Causes


Link failure, software bug


Types of routing instability


Inter
-
domain


Intra
-
domain

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Methodology


Methodology


Use

tcpdump


to collect link state
routing messages


Then analyze the routing messages
by self
-
made tools


Ospfanaly


Some other scripts


Include a CGI perl script to view the statistical
results by web

5


Open Shortest Path First


A widely deployed intra
-
domain link state
routing protocol


OSPFv2 and OSPFv3


Link state advertisements (LSAs)


OSPFv2


Router
-
LSA


Network
-
summary
-
LSA


AS
-
external
-
LSA


OSPFv3


Seven kinds of LSAs defined in RFC2740

OSPF



Network
-
LSA



ASBR
-
summary
-
LSA

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Case Study One: WIDE Internet


WIDE Internet


WIDE Project


http://www.wide.ad.jp


Connecting hundreds of organizations


NARA
-
NOC


Located in Nara Institute of Science and
Technology, Japan


The measurement machine is placed into
one ethernet segment of the NARA
-
NOC
network

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Measurement Result of WIDE Internet (OSPFv2)

Date (Year/Month)

Number of LSA changes

Number of LSAs

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The Case of OSPFv3

Number of LSA changes

Date (Year/Month)

Number of LSAs

9

Other Findings during the Analysis


Sometimes serious LSA oscillation
happened


The change happens with the interval of
10s
-
200s


Usually lasts for hours, sometimes for days


Oscillation of router
-
LSA


Most of the observed oscillation was the
repeated up/down of routers


interfaces

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The Causes of the Flaps


The isolated causes


Congestion


DDoS attacks


Operation miss


Mis
-
configuration of router ID


Software/Hardware bug


Zebra routing daemon


Cisco

s OSPF bug


Foundry switch


The causes of much flaps are still unknown


The flaps occur randomly


Why the flaps decrease in the recent months?


The change of routing protocol implementation style


Special process on routing messages


Bandwidth

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Case Study Two: APAN Tokyo
-
XP


APAN Tokyo
-
XP


Located in Otemachi, Tokyo


Seven routers in the backbone area


Data collected on a FreeBSD box
connected to a ethernet segment

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Measurement Result of APAN
Tokyo
-
XP (OSPFv2)

Number of LSAs

Date (Year/Month)

Number of LSA changes

Although most of the updates are due to router maintenance,

there still unknown ones.

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Conclusion


Our investigation on WIDE Internet


OSPF LSA oscillation may occur frequently
sometimes


Sometimes serious oscillation occurred


It is difficult to determine what caused the
flaps


Similar phenomenon may be found on
other networks, so it is important to
deploy a measurement system on
different networks

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Future Work


To do more measurement on other
networks


Abilene of Internet2


To improve our monitoring system


To isolate the causes


When detects oscillation, obtain
helpful data for troubleshooting

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If you would like to conduct a
routing instability measurement on
your own network, please contact



Zhang Shu

zhang@koganei.wide.ad.jp


Thank you for your attention!