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An Experimental Analysis of BGP Convergence Time

An Experimental Analysis of BGP Convergence Time. Timothy Griffin AT&T Research & Brian Premore Dartmouth College. The problem. There is a considerable delay in BGP convergence after a route change. The configurations on the autonomous system (AS) routers. Solution.

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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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