An Experimental Analysis of BGP Convergence Time

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An Experimental Analysis of BGP Convergence Time

• Timothy Griffin ATT 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

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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!!

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Roadmap

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

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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

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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

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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

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using non-optimal MRAI

• Increase rapidly for MRAI lt optimal
• Increase linearly for MRAI gt optimal

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Roadmap

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

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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, gt200,000 runs, gt1 week

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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

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Roadmap

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

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Roadmap

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

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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

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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?