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A Study of Packet Delivery Performance during Routing Convergence

A Study of Packet Delivery Performance during Routing Convergence. Dan Pei, Lan Wang, Lixia Zhang, UCLA Dan Massey, USC/ISI S. Felix Wu, UC Davis. Packet Delivery during Routing Convergence. D. F. G. A. B. C. E. Failures do occur in the Internet

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A Study of Packet Delivery Performance during Routing Convergence

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  1. A Study of Packet Delivery Performance during Routing Convergence Dan Pei, Lan Wang, Lixia Zhang, UCLA Dan Massey, USC/ISI S. Felix Wu, UC Davis

  2. Packet Delivery during Routing Convergence D F G A B C E • Failures do occur in the Internet • 20% of intra-ISP links have a MTTF < 1 day [Diot:IMW02] • 40% of Inter-ISP routes have a MTT-Change < 1 day [Labovitz:FTCS-29] • Routing convergence after failure takes time • IS-IS(Intra-ISP protocol): 5+ seconds [Diot:IMW02] • BGP(Inter-ISP protocol): 3+ minutes [Labovitz:Sigcomm00] • Packets can be delivered during convergence

  3. Goal of this paper • How to maximize packet delivery during routing convergence? • Previous work focused on: preventing loops, minimizing convergence time and routing overhead • Topological connectivity’s impact? • Studying: RIP, Distributed Bellman-Ford(DBF), BGP • This problem becomes more important with • Larger Internet topology [Huston01] --> higher freq. of component failures • Richer connectivity[Huston01] --> potentially helps with more alternate paths • Higher bandwidth --> more packets sent during convergence

  4. Outline for the rest of the talk • Introduction of RIP, DBF and BGP • Simulation results and lessons learned • Conclusion

  5. Protocols Examined (I):RIP and DBF Distributed Bellman-Ford(DBF) • Keep distance info from all neighbors D D:3 D:2 D:1 Both RIP and DBF: F • 30sec refreshing interval • Damping timer to space out two triggered updates: 1~5 seconds • Poison reverse: B sends infinity distance to A D:2 A B C E D: infinity D:3 RIP • Exchange distance info. • B’s route to D: Nexthop=A, Dist=4 • B’s route to D: Nexthop=A, dist=4 Alternate Nexthop=C, Dist=4 • Keep shortest path only

  6. Protocols Examined (II): BGP D D:<A E F> D:<E F> D:<F> D: <B A E F> F B’s route to D: D:<E F> B A C E D:<C E F> • BGP is similar to DBF, but route includes entire path BGP: damping timer: 25 ~ 35 seconds BGP’: damping timer: 1~5 seconds † Route via A = <A E F> Route via C = <C E F>

  7. Outline for the rest of the talk • Introduction of RIP, DBF and BGP • Simulation results and lessons learned • Conclusion

  8. Simulation conducted 20 pkts/second • 7 by 7 mesh topologies similar those in [Baran64] • Simulated node degree range [3 ~ 16] • MeasurePacket loss, loops, path convergence time, throughput, and e2e delay.

  9. Packet Losses (I) : Observation • Packet losses of DBF, BGP’ and BGP decrease to zero at degree 6. • Richer connectivity helps RIP little. Packet Loss RIP DBF, BGP’ and BGP Node Degree

  10. Packet Loss(II): Lessons Learned RIP: D D DBF, BGP: F F B E C B E A C A • Keeping alternate paths • Connectivity Matters • no immediate available alternative due to poor connectivity and poison reverse • alternative is more likely with richer connectivity

  11. Packet Loss(III): Is an alternate path valid? D: < > D: < > D: < > D W C2 F V X U A B C E • Valid Alternate Paths: not using the failed link • Poison reverse and BGP’s path information are not enough! [Pei:Infocom2002] • Richer connectivity --> • reduces one single link’s impact • better availability of valid(but may be suboptimal) path

  12. Transient Loops(I): Observation • BGP has the most loops! • RIP has no loops • Richer connectivity reduces the chance of looping. BGP Losses due to loops BGP’ DBF Node Degree

  13. Transient Loops(II): Msg Propagation D: < > D: < > D: < > D: < > D: < > D D: <BC A E F> D: <B A E F> W F V U Y X D:<C B A E F> E C B A D:<C A E F> 30 seconds! • Damping timer slows the msg propagation, causing looping • Richer connectivity can reduce the chance of looping • More details in: “A Study of Transient Loops in BGP”

  14. Conclusion • Network’s Ultimate goal is to deliver happy packets, so Routing Protocols should • Maximize packet delivery during convergence • Achieve a good balance between packet delivery AND loop prevention, routing conv. time and routing overhead • Utilize the connectivity redundancy • Future work • Apply insights to BGP; study link state protocols, e2e TCP performance; Larger topologies, multiple pairs of S/D, multiple failures

  15. Questions?

  16. Instantaneous Throughput BGP’ Throughput(pkts/second BGP DBF RIP RIP Time

  17. Packet Delay During Convergence

  18. Forwarding Path Convergence time Time till the forwarding path from S to D stabilizes. Time till there is no routing msg. BGP:13 BGP:70 BGP’:2 BGP’:10 • BGP: no loss at degree 6 or higher • Shall we still tune MRAI timer to minimize convergence time(with the risk of increasing overhead)? Node Degree

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