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IRTF-RR

IRTF-RR. ahuja@umich.edu. IRTF agenda. Agenda issues (5 sec) Intro - why are we here (10 sec) - abha Goals of the group, etc (30 min)- sean Topics of Interest Convergence (10 minutes) - abha Nimrod (20 minutes) - noel Questions and Answers/Feedback. IRTF RR intro. Who are we?

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IRTF-RR

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  1. IRTF-RR ahuja@umich.edu

  2. IRTF agenda • Agenda issues (5 sec) • Intro - why are we here (10 sec) - abha • Goals of the group, etc (30 min)- sean • Topics of Interest • Convergence (10 minutes) - abha • Nimrod (20 minutes) - noel • Questions and Answers/Feedback

  3. IRTF RR intro • Who are we? • ahuja@umich.edu • smd@ebone.net • irtf-rr-chairs@nether.net • Where is the info? • http://www.nether.net/irtf-rr • irtf-rr-request@nether.net

  4. IRTF RR • Why are we here? • Resurrect this working group • Open session to tell folks what we are working on • Get feedback from the public for additional topics to add to our list

  5. IRTF-RR goals • do routing research :) • most of work done in mailing list and small groups

  6. Approaching the issues... • What is going on now? • Routing issues today • What are the problems? • What can we do fix it? • What should we do in the future?

  7. Routing Research • Topics of interest • routing convergence, stability and scalability • fault tolerance • Quality of Service routing • multicast routing • Extremely dynamic contraint-based routing • Traffic engineering • NAT and IPv6 routing • optical networks and routing • operational concerns of routing

  8. Q&A • What issues do you think are important to address? • QoS? • Convergence? • Scalability?

  9. Experimental Measurement of Delayed Convergence Craig Labovitz Microsoft Research/Merit Network, Inc. Abha Ahuja Merit Network, Inc. Farnam Jahanian, Abhijit Bose University of Michigan Slides originally presented at NANOG. IRTF-RR at Pittsburgh IETF email: ahuja@umich.edu

  10. Mostly seems to work Time Mostly seems to work The Internet: Failure Analysis Something happens. Doesn’t work.

  11. Routing Protocol Convergence • Unlike connection oriented PSTN (~30 ms), Internet does not have fail-over. • Instead, each node recalculates on a hop-per-hop basis (i.e. no flooding of changes) • Distance-vector algorithms (e.g. RIP, BGP) exhibit slower convergence than link state protocols • During convergence • Latency, loss, out of order • Additional update messages (CPU processing)

  12. Distance Vector (BF) Protocols • Suffer from counting to infinity problem • Solutions • Poison reverse • Split horizon • Path vectors B Example A C

  13. Conventional Wisdom • “Restoral is not an issue in the IP world” • Just reroute around in a few milliseconds or whatever • BGP convergence takes only a few _____ • “Bad news travels fast” • Fast withdraw propagation valid goal • Announcements slower because bundled • BGP has great convergence properties • ASPath solved the convergence and counting to infinity problems • All my customers are multi-homed, triple-homed • Convergence -- what, me worry?

  14. More Conventional Wisdom • Enough bandwidth will solve anything “It will all be one big network one day soon anyways” (Especially after yesterday)

  15. Internet Failures • Replication, round-robin DNS, etc. helps reliability of inter-domain content oriented services • Inter-domain transaction oriented services (e.g. VoIP, EBay, database commits, etc.) still pose a challenge • Important model how long does it take for the Internet to converge • After Failure • After Fail-Over • After Repair

  16. BGP: Bad news • With unconstrained policies (Griffin99, Varadhan96) • Divergence • Possible create mutually unsatisfiable policies • NP-complete to identify these policies in IRR • Happening today? • With constrained policies (e.g. shortest path first) • Transient oscillations • BGP usually converges • It might just take a very long time…. • This talk is about constrained policies

  17. Some Observations • How do we study convergence? • From BGP logs (e.g. debug ip bgp), difficult to determine causal relationships • Earlier work studied BGP pathologies and failures • Still lots of BGP duplicates and oscillations • Failure/repair data (next slide) for default-free routes shows 30 minute curve • Examined long-lived default-free routes from 24 providers for a year • Restoral time for given provider after failure (i.e. route withdrawn)

  18. How long until routes return? (From A Study of Internet Failures) What is happening here?

  19. 16 Month Study of Convergence • Instrument the Internet • Inject routes into geographically and topologically diverse provider BGP peering sessions (Mae-West, Japan, Michigan, London) • Periodically fail and change these routes (i.e. send withdraws or new attributes) • Time events using ICMP echos and NTP synchronized BGP “routeviews” monitoring machines (also http gets) • Write lots of Perl scripts • Wait a sixteen months… (45,000 routing events)

  20. Setup

  21. How Many Announcements Does it Take For an AS to Withdraw a Route? 7/5 19:33:25 Route R is withdrawn 7/5 19:34:15 AS6543 announceR 6543 66665 8918 1 5696 999 7/5 19:35:00 AS6543 announceR 6543 66665 8918 67455 6461 5696 999 7/5 19:35:37 AS6543 announceR 6543 66665 4332 6461 5696 999 7/5 19:35:39 AS6543 announceR 6543 66665 5378 6660 67455 6461 5696 999 7/5 19:35:39 AS6543 announceR 6543 66665 65 6461 5696 999 7/5 19:35:52 AS6543 announceR 6543 66665 6461 5696 999 7/5 19:36:00 AS6543 announceR 6543 66665 5378 6765 6660 67455 6461 5696 999 … 7/5 19:38:22 AS6543 withdrawR Answer: Up to 19 (AS6543 chosen as an example – all AS’es exhibit similar behavior) Abha made me change the AS numbers

  22. Withdraw Convergence After a BGP route is withdrawn, barring other failures, how long does it take Internet routing tables to reach steady-state?

  23. Withdraw Convergence AS1 AS2 AS3 AS4

  24. Withdraw Convergence • Probability distribution • Providers exhibit different, but related convergence behaviors • 80% of withdraws from all ISPs take more than a minute • For ISP4, 20% withdraws took more than three minutes to converge

  25. Fail-Overs and Repairs What are the relative convergence latencies for fail-overs and repairs? Does bad news (withdraws) travel faster?

  26. Failures, Fail-overs and Repairs

  27. Failures, Fail-overs and Repairs • Bad news does not travel fast… • Repairs (Tup) exhibit similar convergence properties as long-short ASPath fail-over • Failures (Tdown) and short-long fail-overs (e.g. primary to secondary path) also similar • Slower than Tup (e.g. a repair) • 60% take longer than two minutes • Fail-over times degrade the greater the degree of multi-homing!

  28. What is Happening? • Non-deterministic ordering of BGP update messages leads to • Transient oscillations • Each change in FIB adds delay (CPU, BGP bundling timer) • At extreme, convergence triggers BGP dampening

  29. ABCD BACD CBAD DBCA ABDC BADC CBDA DBAC ACBD BCAD CABD DCBA ADBC BDAC CDBA DABC ACDB BCDA CADB DCAB ADCB BDCA CDAB DACD A B C D BGP and RIP • RIP precisely monotonically increasing. Can explore metrics (1…N) • BGP monotonically increasing. Multiple (N!) ways to represent a path metric of N. • BGP “solved” RIP routing table loop problem by making it exponentially worse… N=4

  30. Questions? send email to ahuja@umich.edu

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