(c) Anirban Banerjee, Winter 2005, CS-240, 2/1/2005. The Impact of Internet Policy and Topology on Delayed Routing convergence C. Labovitz, A. Ahuja, R. Wattenhofer and S. Venkatachary. IEEE INFOCOM 2001.

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

The “Problem” The internet lacks inter-domain path fail over. How soon can convergence be expected when path(s) fail. What is the effect of path failures on different ISPs, large and small.

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

The “Contribution” Demonstrate that the time for end-to-end internet convergence depends on the length of the length of the longest possible back-up AS path between source and destination node. Show clearly, larger ISPs have faster convergence latencies.

The “Contribution”..more specifically Time complexity of for internet fail-over convergence is upper bounded by 30n sec. Show that, routes from customers of larger ISPs exhibit faster convergence. Presence of “vagabond” paths, s/w errors. Most default free Internet routes exhibit multiple alternate secondary paths.

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

Motivation There is a relative lack of reliability in the internet vis-à-vis the PSTN network. Multi-homed internet sites often experience long connectivity latencies after faults(s) occur.

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

Background BGP, a path vector protocol, uses an ASPath sequence of intermediate ASs. Uses this ASPath for loop detection and policy decisions. Most vendor implementations of BGP fall back on the best path selection based on ASPath length after fault.

Background..contd. BGP includes a MinRouteAdver timer. This provides a buffer between BGP updates and also allows for aggregation of routes containing common information. T. Griffin and G. Wilfong, “An analysis of BGP convergence properties”, ACM SIGCOM, {possible to implement mutuall unsatisfiable policies in BGP} L. Gao and J. Rexford,”Stable Internet Routing without Global Coordination”, ACM SIGMETRICS, 2000.{adherence to common policies guarantees convergence}

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

TestBed Unix, probe machineswith peering sessions with more than 20 ISPs (geographically and topologically diverse). Inject faults into more than 10 ISPs. Software from MRT & IPMA projects, running on FreeBSD systems. Observation spread over 6 months.

Routing Policy Most ISPs simply resort to trusting their peers. ! ! ! !

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

Experimental Results Effect of topology on Convergence Analyzed routing topologies between more than 200 pair of ISPs. Focus on MinRouteAdver Timers and length of ASPaths on convergence.

Experimental Results Routes from ISP1

Experimental Results Routes from ISP2

Experimental Results Routes from ISP3

Experimental Results

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

Conclusions Shown conclusively that the internet currently lacks high levels of reliability and fault tolerance. Current internet convergence latencies, upto 15 min. is very high. Complexity of multi homed internet path fail over scales with the longest possible back up path for that route. Customers sensitive to fail overs, should multi home to larger ISPs. There remains a chasm in formulating nechanisms to handle “vagabond” paths.

Roadmap The “Problem” The “Contribution” Motivation Background Testbed Experimental Results Conclusions Future Work

Evolve mechanism to handle “vagabond” paths. Implement necessary changes to BGP in order to reduce convergence latencies.

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