17-ARouting - Recent Developments in Routing EE122 Fall...

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1 Recent Developments in Routing EE122 Fall 2011 Scott Shenker http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks to Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley
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How about trying undergraduate research? Work at cutting edge of EECS Meet profs, grad students outside class See if you’d enjoy graduate school Make résumé more competitive Prof. Armando Fox will give an informal presentation on getting started in undergrad research on Tuesday, Nov. 15, 6pm in the Woz (he s the one on the left)
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Announcements • New homework policy: – Assignments: easy – Worksheet: hard (material will be on final) • All regrade requests should be in…. • Project 3: an introduction to it next lecture – Rearranged lecture schedule, so I will give SDN talk – Followed by presentations on project itself – Can do project without SDN (that’s the point of SDN!), but you won’t know why it is so cool…. 3
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Holy Trinity of Routing: LS, DV, PV • Normally presented as the complete story • But we know how to do much better – Some hacks deployed today – Some research proposals not deployed. • That is what we will talk about today…. . 4
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Another Purpose for Today • EE122 (CS version) is algorithmically vacuous – AIMD is the high point of intellectual depth (ugh) • The algorithms described today are nontrivial – Algorithms simple, but their properties are nonobvious You will prove two results as a class exercise – 5 minutes, in groups, try to come up with reasoning – I’ll help shape it into a proof 5
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RoutingChallenge: Resilience • Basic routing algorithms rely on timely consistency or global convergence to achieve ensure delivery – LS: routers need to have same picture of network – PV/DV: if algorithm hasn’t converged, might loop • As nets grow, this gets harder and takes longer Need both consistency/convergence and timeliness! • Lag between failure detection and recovery – Lag is biggest barrier to achieving 99.999% reliability 6
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Hacks Used Today • Preconfigured backup paths – When link fails, router has a backup route to use – Very helpful against single failures – Only limited protection against multiple failures – No systematic paradigm • ECMP: Equal-Cost Multipath – Similar to backups, but narrower applicability – Choose among several “shortest-paths” 7
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Solutions Presented Today • Multipath (one slide) • Failure-carrying packets • Routing-along-DAGs • Preventing policy oscillations (if time) 8
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Multipath Routing • Multipath: – Providing more than one path for each S-D pair – Allow endpoints to choose among them • Good: if one path goes down, can use another • Bad: Delay while endpoints detect failure (RTT) • Absolutely necessary because of E2E arguments But not a fundamental paradigm shift Part of solution, but still need more reliable routing 9
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Can we completely eliminate the need to reconverge after link failures? i.e., can we tolerate failures without losses?
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17-ARouting - Recent Developments in Routing EE122 Fall...

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