1. DSN 2003 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. DSN 2003 06/24/2003 2/14 Packet Delivery during Routing Convergence 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 ABC E F D G

3. DSN 2003 06/24/2003 3/14 Goal of this paper How to maximize packet delivery during routing convergence? Topological connectivity’s impact? Studying: RIP, Distributed Bellman-Ford(DBF), BGP Previous work focused on: preventing loops, minimizing convergence time and routing overhead 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. DSN 2003 06/24/2003 4/14 Outline for the rest of the talk Introduction of RIP, DBF and BGP Simulation results and lessons learned Conclusion

5. DSN 2003 06/24/2003 5/14 Protocols Examined (I):RIP and DBF RIP Keep shortest path only Distributed Bellman-Ford(DBF) Keep distance info from all neighbors A B C EF D D:1 D:3 D:2 D:3 B’s route to D: Nexthop=A, Dist=4 B’s route to D: Nexthop=A, dist=4 Alternate Nexthop=C, Dist=4 D: infinity 30sec refreshing interval Damping timer to space out two triggered updates: 1~5 seconds Poison reverse: B sends infinity distance to A Both RIP and DBF: Exchange distance info.

6. DSN 2003 06/24/2003 6/14 BGP is similar to DBF, but route includes entire path Route via A = Route via C = B’s route to D: A B C E F D D: BGP: damping timer: 25 ~ 35 seconds BGP’: damping timer: 1~5 seconds  Protocols Examined (II): BGP D:

7. DSN 2003 06/24/2003 7/14 Outline for the rest of the talk Introduction of RIP, DBF and BGP Simulation results and lessons learned Conclusion

8. DSN 2003 06/24/2003 8/14 Simulation conducted 7 by 7 mesh topologies similar those in [Baran64] 20 pkts/second Measure Packet loss, loops, path convergence time, throughput, and e2e delay. Simulated node degree range [3 ~ 16]

9. DSN 2003 06/24/2003 9/14 Packet Losses (I) : Observation RIP DBF, BGP’ and BGP Packet losses of DBF, BGP’ and BGP decrease to zero at degree 6. Richer connectivity helps RIP little. Node Degree Packet Loss

10. DSN 2003 06/24/2003 10/14 Packet Loss(II): Lessons Learned Keeping alternate paths F D A B C E F D A B C E Connectivity Matters no immediate available alternative due to poor connectivity and poison reverse RIP: DBF, BGP: alternative is more likely with richer connectivity

11. DSN 2003 06/24/2003 11/14 Packet Loss(III): Is an alternate path valid? Valid Alternate Paths: not using the failed link Poison reverse and BGP’s path information are not enough! [Pei:Infocom2002] F D A B C E U X V W Richer connectivity --> reduces one single link’s impact better availability of valid(but may be suboptimal) path C2 D:

12. DSN 2003 06/24/2003 12/14 Transient Loops(I): Observation DBF BGP’ BGP BGP has the most loops! RIP has no loops Richer connectivity reduces the chance of looping. Node Degree Losses due to loops

13. DSN 2003 06/24/2003 13/14 F D A B C E Transient Loops(II): Msg Propagation Damping timer slows the msg propagation, causing looping U X V W Y D: Richer connectivity can reduce the chance of looping More details in: “A Study of Transient Loops in BGP” 30 seconds! D:

14. DSN 2003 06/24/2003 14/14 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. DSN 2003 Questions?

16. DSN 2003 06/24/2003 16/14 Instantaneous Throughput RIP DBF BGP’ BGP RIP Time Throughput(pkts/second

17. DSN 2003 06/24/2003 17/14 Packet Delay During Convergence

18. DSN 2003 06/24/2003 18/14 Forwarding Path Convergence time 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 BGP:70 BGP’:10 Time till there is no routing msg. BGP:13 BGP’:2 Time till the forwarding path from S to D stabilizes.

19. DSN 2003 06/24/2003 19/14