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Case Studies on Intra-Domain Routing Instability

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. Overview. What is routing instability?

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Case Studies on Intra-Domain Routing Instability

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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

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

  3. 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

  4. 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. OSPF • 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 • Network-LSA • ASBR-summary-LSA

  6. 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

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

  8. The Case of OSPFv3 Number of LSA changes Number of LSAs Date (Year/Month)

  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

  10. 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

  11. 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

  12. Measurement Result of APAN Tokyo-XP (OSPFv2) Number of LSA changes Number of LSAs Date (Year/Month) Although most of the updates are due to router maintenance, there still unknown ones.

  13. 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

  14. 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

  15. If you would like to conduct a routing instability measurement on your own network, please contact Zhang Shuzhang@koganei.wide.ad.jpThank you for your attention!

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