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An Experimental Analysis of BGP Convergence Time

This experimental analysis delves into the considerable delay in BGP convergence post a route change. By simulating various router configurations, the study seeks to identify the optimal setup for minimal convergence time to address issues like packet loss and disruption of connectivity. The research explores BGP routing mechanisms, configurable options at the router level, and simulation of network settings to compare analysis options against convergence time, offering insights for improving network stability. Key observations emphasize the impact of MRAI values, SSLD, and WRATE on convergence time and message exchanges, stressing the significance of configuring routers optimally. Utilizing the SSFNet simulation package and conducting extensive runs, the study provides a focused approach to understanding and enhancing BGP convergence efficiency. Conclusively, it suggests fine-tuning MRAI settings on BGP routers to achieve minimal convergence time, highlighting the need for continued research to adapt configurations based on network dynamics and changes.

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An Experimental Analysis of BGP Convergence Time

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  1. An Experimental Analysis of BGP Convergence Time Timothy Griffin AT&T Research & Brian Premore Dartmouth College

  2. The problem • There is a considerable delay in BGP convergence after a route change. • The configurations on the autonomous system (AS) routers

  3. Solution • By simulating a set of different router configurations, • find the optimal configuration in which the convergence time is minimal.

  4. Importance • There is a considerable convergence delay after a route change • Before the network converges • packet loss • packet delay • disruption of connectivity

  5. Roadmap • BGP routing & reasons for long convergence time • Some configurable options in BGP level routers • Simulation network settings • Analysis options vs. convergence time • Summary

  6. BGP routing • How BGP routing work • distance-vector algorithm • Two types of update messages • Advertisements • withdrawals

  7. Long convergence time • Nature of BGP path selection • Routers enumerate multiple paths • Eliminate and replacing other choices • Minimum Route Advertisement Interval • MRAI, usually 30 seconds (hardcode) • Add delays • Not guaranteed converge!!

  8. Roadmap • BGP routing & reasons for long convergence time • Some configurable options in BGP level routers • Simulation network settings • Analysis options vs. convergence time • Summary

  9. Router configurations • MRAI • Too high: longer delay between update message • Too low: oscillation of update message among routers  more update messages • SSLD • Sender side loop detection • WRATE • Withdrawal rate limiting

  10. Observations • Depend on the network … • There is an optimal value of MRAI to minimize the number of update messages needed to be sent • There is another optimal value of MRAI to minimize the convergence time • The affects of not using optimal value of MRAI • Very similar for all networks • The affect of using SLLD and WRITE • Good and bad depends on the networks

  11. optimal values of MRAI • number of update/withdrawal messages sent • MRAI small, oscillation • MRAI large … • the convergence time • MRAI small … • MRAI large, longer to wait between messages

  12. using non-optimal MRAI • Increase rapidly for MRAI < optimal • Increase linearly for MRAI > optimal

  13. Roadmap • BGP routing & reasons for long convergence time • Some configurable options in BGP level routers • Simulation network settings • Analysis options vs. convergence time • Summary

  14. Simulation setting • SSFNet • Java-based simulation package • IP-level • BGP-4 supported natively • Networks • Simple topology • CLIQUE, CHAIN, RING, FOCUS, P-CLIQUE • Limited size (5-20 nodes) • Combinations of MRAI values, SSLD & WRATE • Perl script, >200,000 runs, >1 week

  15. More on simulation setting • One AS is one node in the network • Only a single link update or withdrawal each time • All routers have the same configurations • No commercial extension • Using network which guaranteed converge • Random delays on processing route updates

  16. Roadmap • BGP routing & reasons for long convergence time • Some configurable options in BGP level routers • Simulation network settings • Analysis options vs. convergence time • Summary

  17. Roadmap • BGP routing & reasons for long convergence time • Some configurable options in BGP level routers • Simulation network settings • Analysis options vs. convergence time • Summary

  18. Conclusion • We can configure the MRAI on BGP level routers to minimize convergence time. • The optimal value depends on the network • Having a higher MRAI value tends to be safer

  19. Future work • We know there is a optimal settings • It depends on topology, link changes, … • How can we configure the routers so the convergence time is close to the optimal value?

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