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

2 Overview What is routing instability? What is routing instability? Methodology of the measurement Methodology of the measurement Case study 1: WIDE Internet Case study 1: WIDE Internet Case study 2: APAN Tokyo-XP Case study 2: APAN Tokyo-XP Conclusion and future work Conclusion and future work

3 Routing Instability Routing instability Routing instability Also called route flapsAlso called route flaps Unexpected topology changeUnexpected topology change Bad influence Bad influence Packet lossPacket loss Increased router loadIncreased router load Wasted bandwidthWasted bandwidth Causes Causes Link failure, software bugLink failure, software bug Types of routing instability Types of routing instability Inter-domainInter-domain Intra-domainIntra-domain

4Methodology Methodology Methodology Use “ tcpdump ” to collect link state routing messagesUse “ tcpdump ” to collect link state routing messages Then analyze the routing messages by self-made toolsThen analyze the routing messages by self-made tools Ospfanaly Ospfanaly Some other scripts Some other scripts Include a CGI perl script to view the statistical results by webInclude a CGI perl script to view the statistical results by web

5 Open Shortest Path First Open Shortest Path First A widely deployed intra-domain link state routing protocolA widely deployed intra-domain link state routing protocol OSPFv2 and OSPFv3OSPFv2 and OSPFv3 Link state advertisements (LSAs) Link state advertisements (LSAs) OSPFv2OSPFv2 Router-LSA Router-LSA Network-summary-LSA Network-summary-LSA AS-external-LSA AS-external-LSA OSPFv3OSPFv3 Seven kinds of LSAs defined in RFC2740 Seven kinds of LSAs defined in RFC2740 OSPF Network-LSA Network-LSA ASBR-summary-LSA ASBR-summary-LSA

6 Case Study One: WIDE Internet WIDE Internet WIDE Internet WIDE ProjectWIDE Project Connecting hundreds of organizationsConnecting hundreds of organizations NARA-NOC NARA-NOC Located in Nara Institute of Science and Technology, JapanLocated in Nara Institute of Science and Technology, Japan The measurement machine is placed into one ethernet segment of the NARA-NOC networkThe measurement machine is placed into one ethernet segment of the NARA-NOC network

7 Measurement Result of WIDE Internet (OSPFv2) Date (Year/Month) Number of LSA changes Number of LSAs

8 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 Sometimes serious LSA oscillation happened The change happens with the interval of 10s-200sThe change happens with the interval of 10s-200s Usually lasts for hours, sometimes for daysUsually lasts for hours, sometimes for days Oscillation of router-LSA Oscillation of router-LSA Most of the observed oscillation was the repeated up/down of routers ’ interfacesMost of the observed oscillation was the repeated up/down of routers ’ interfaces

10 The Causes of the Flaps The isolated causes The isolated causes CongestionCongestion DDoS attacks DDoS attacks Operation missOperation miss Mis-configuration of router ID Mis-configuration of router ID Software/Hardware bugSoftware/Hardware bug Zebra routing daemon Zebra routing daemon Cisco ’ s OSPF bug Cisco ’ s OSPF bug Foundry switch Foundry switch The causes of much flaps are still unknown The causes of much flaps are still unknown The flaps occur randomlyThe flaps occur randomly Why the flaps decrease in the recent months? Why the flaps decrease in the recent months? The change of routing protocol implementation styleThe change of routing protocol implementation style Special process on routing messages Special process on routing messages BandwidthBandwidth

11 Case Study Two: APAN Tokyo-XP APAN Tokyo-XP APAN Tokyo-XP Located in Otemachi, TokyoLocated in Otemachi, Tokyo Seven routers in the backbone areaSeven routers in the backbone area Data collected on a FreeBSD box connected to a ethernet segmentData collected on a FreeBSD box connected to a ethernet segment

12 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.

13 Conclusion Our investigation on WIDE Internet Our investigation on WIDE Internet OSPF LSA oscillation may occur frequently sometimesOSPF LSA oscillation may occur frequently sometimes Sometimes serious oscillation occurredSometimes serious oscillation occurred It is difficult to determine what caused the flapsIt 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 Similar phenomenon may be found on other networks, so it is important to deploy a measurement system on different networks

14 Future Work To do more measurement on other networks To do more measurement on other networks Abilene of Internet2Abilene of Internet2 To improve our monitoring system To improve our monitoring system To isolate the causes To isolate the causes When detects oscillation, obtain helpful data for troubleshootingWhen detects oscillation, obtain helpful data for troubleshooting

15 If you would like to conduct a routing instability measurement on your own network, please contact Zhang Shu Thank you for your attention!