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Putting BGP on the Right Path: A Case for Next-Hop Routing

Putting BGP on the Right Path: A Case for Next-Hop Routing. Michael Schapira Joint work with Yaping Zhu and Jennifer Rexford (Princeton University). Once Upon a Time… Internet Inter-Network Routing:. Small network Single administrative entity NSFNET Shortest-path routing

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Putting BGP on the Right Path: A Case for Next-Hop Routing

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  1. Putting BGP on the Right Path: A Case for Next-Hop Routing Michael Schapira Joint work with Yaping Zhu and Jennifer Rexford (Princeton University)

  2. Once Upon a Time… Internet Inter-Network Routing: • Small network • Single administrative entity • NSFNET • Shortest-path routing • distance-vector routing • Then....

  3. Interdomain Routing Over 35,000 Autonomous Systems (ASes) Interdomain routing = routing between ASes • Border Gateway Protocol (BGP) Sprint AT&T Comcast Qwest

  4. Today’s Path-Based Routing With BGP • Complex! • configuration errors, software bugs, … • Bad convergence! • persistent route oscillations, slow convergence, … • Vulnerable to attacks! • malicious, economically-driven, inadvertent, … • and more, and more, and more … • bad performance, clumsy traffic engineering, …

  5. How Can We FixInterdomain Routing? • One approach: add mechanisms to an already complex protocol • route flap damping, S-BGP, … • Another approach: redesign interdomain routing from scratch • HLP, NIRA, pathlet routing, consensus routing, … • Our approach: simplify BGP!

  6. Background: Today’s Path-Based Routing With BGP Choosesingle “best”route (ranking) Send route updates to neighbors (export policy) Receive route updates from neighbors • AS i’srouting policy: • ranking of simple routes from i to each destination d • export policy • BGP is apath-vector protocol

  7. Background: Today’s Path-Based Routing With BGP 3, I’m using 1d 32d > 31d 1 1, 2, I’m available 3 d 2 Don’t export 2d to 3 a stable state is reached

  8. AS-PATH = the Route of All Evil • AS-PATH: list of allASes on path • originally meant for loop-detection • The AS-PATH is to blame! • error-prone, software bugs • no/slow convergence • large attack surface • bad scalability, clumsy traffic engineering, bad performance, …

  9. Getting Off the AS-PATH • No way back to shortest-path routing… • Our proposal: next-hop routing • make routing decisions based solely on the “next hop” • relegate the AS-PATH to its original role

  10. Wish List • Loop freedom • Fast Convergence • Security • Incentive compatibility • Business policies • Good performance • Traffic engineering • Scalability • Simplicity

  11. Expressiveness vs. Complexity complexity BGP’spath-basedrouting too complex shortest-pathrouting next-hoprouting simple expressiveness sufficientlyexpressive not expressiveenough extremelyexpressive

  12. Next-Hop Routing Rules! • Rule 1: use next-hop rankings 541d > 53d > 542d 4 > 3 1 4 d 5 2 3

  13. Next-Hop Routing Rules! • Rule 1: use next-hop rankings • Rule 2: prioritize current route • to minimize path exploration[Godfrey-Caesar-Hagen-Singer-Shenker] 2=3 Prioritize current route 2=3 Break ties in favor of lower AS number 2 d 1 3

  14. Next-Hop Routing Rules! • Rule 1: use next-hop rankings • Rule 2: prioritize current route • Rule 3: consistently export • to avoid disconnecting upstream nodes[Feigenbaum-S-Ramachandran] 1 > 2, Export 32d, but not 31d, to 4 1 > 2, Export 31dto 4 1 d 4 3 2

  15. Next-Hop Routing Rules! • Rule 1: use next-hop rankings • Rule 2: prioritize current route • Rule 3: consistently export • Defn: Node iconsistently exports w.r.t. neighbor j if there is some route Rs.t. each route Q is exportable to j iffR ≤iQ. • Defn: Node iconsistently exports if it consistently exports with respect to each neighboring node j.

  16. Next-Hop Routing Rules! • Rule 1: use next-hop rankings • Rule 2: prioritize current route • Rule 3: consistently export • 3 deployment schemes • Configure today’s routers • Create new router configuration interface • Build new router software

  17. Wish List Revisited • Loop freedom • Fast convergence • Security • Incentive compatibility • Business policies • Good performance • Traffic engineering • Scalability • Simplicity

  18. Wish List Revisited • Loop freedom • Fast convergence? • Security • Incentive compatibility [Feigenbaum-S-Ramachandran] • Business policies • Good performance • Traffic engineering • Scalability? • Simplicity

  19. Existence of Stable State • Existence of stable state not guaranteed even with next-hop rankings (Rule 1) [Feamster-Johari-Balakrishnan] • Thm: If the next-hop routing rules hold, then a stable state exists in the network. • What about (fast!) convergence?

  20. BGP Oscillations BGP not guaranteed to converge even with next-hop routing! [Griffin-Shepherd-Wilfong] 1 2 2 > d 1 > d d

  21. The Commercial Internet • ASes sign long-term contracts. • Neighboring pairs of ASes have: • a customer-provider relationship • a peering relationship peer providers peer customers

  22. Gao-Rexford Framework • 3 simple conditions that are naturally induced by the AS-business-hierarchy. • Topology condition, Preference condition, Export condition • If the Gao-Rexford conditions hold, then BGP is guaranteed to converge to a stable state. [Gao-Rexford] • But, this might require exponentially-many forwarding changes! [Syed-Rexford]

  23. Fast BGP Convergence • Thm: In the Gao-Rexford framework, next-hop routing convergence to a stable state involves at most O(L2) forwarding changes(L = # links). • all network topologies • all timings of AS activations and update message arrivals • all initial routing states • all initial “beliefs” • implications for routing changes and number of BGP updates

  24. Simulations • C-BGP simulator. Cyclops AS-level topology, Jan 1st 2010(33,976 ASes, ~5000 non-stubs) • Protocols:BGP, Prefer Recent Route (PRR), next-hop routing • Metrics:# forwarding changes, # routing changes,# updates, AS-PATH length • Events:prefix up, link failure, link recovery • Methodology: 500 experiments, 10,000 vantage points (all non-stubs, 5000 stubs)

  25. Simulation Results(# Forwarding Changes) maximum number of routing changes in next-hop routing = 3 maximum number of forwarding changesin PRR = 10 maximum number of BGP forwarding changes > 20

  26. Simulation Results(# Routing Changes) maximum number of routing changes in next-hop routing < 20 maximum number of BGP routing changes > 160 maximum number of routing changesin PRR > 40

  27. Simulation Results(# BGP Updates, Non-Stub ASes) maximum number of updates in next-hop routing < 300 maximum number of updates in PRR > 1000 maximum number of BGP updates > 6000

  28. Simulation Results(# Routing Changes, The 0.1% Position)

  29. Incentive Compatible Routing Configurations 3 > d > 1 2 2 d > 2 3 1 d Each node is getting its best feasible next-hop

  30. Next-Hop Routing isIncentive Compatible • Thm [Feigenbaum-Ramachandran-S]: In the Gao-Rexford framework, next-hop routing is incentive compatible. (each node is guaranteed its bestfeasible next-hop)

  31. Wish List Revisited • Loop freedom • Fast convergence • Security? • Incentive compatibility • Business policies • Good performance? • Traffic engineering? • Scalability • Simplicity

  32. Limitations of Next-Hop Routing • AS-PATH length • AS-avoiding policies • AS-name prepending • AS-PATH-based traffic engineering

  33. Security, Performance,Traffic Engineering • Still open research questions. • Handled mostly outside the routing protocol. • We argue that next-hop routing makes things mostly better.

  34. Performance • Faster/better convergence than BGP. • much more scalable. • But…potential increase in path lengths. • b • loosely correlated with performance (# routers, physical distance… throughput…). • still, significant increase clearly undesirable! • Simulation results: same path length for 97-99% of ASes; big increase only for ~0.1%.

  35. Security • Reduces BGP’s attack surface (AS-PATH length plays no role in routing decisions). • More resilient to economically-driven attacks (incentive compatible). • More resilient to misconfigurations(in progress) • But… AS-avoiding policies impossible. • come with no guarantees. e2e?

  36. Traffic Engineering • We discuss how traffic engineering can be done without relying on the AS-PATH. • using different next-hop rankings for different (groups of) prefixes • using the BGP communities attribute • …

  37. Multipath Routing • Performance, security and traffic engineering can greatly benefit from multipath routing. • multiple working paths • immediate response to failures • load balancing among multiple next-hops • … • Next-hop routing lowers the barrier for making this a reality (work in progress).

  38. Multipath Routing • Exploiting path diversity to • realize the AS’s own objectives • customize route selection for neighboringASes • But... multipath routing is not scalable! • disseminate and store multiple routes

  39. Multipath Routing is Not Scalable! I’m using P1 and P2 1 P1 I’m using P1, P2, Q1 and Q2 P2 d 4 3 Q1 I’m using Q1 and Q2 2 Q2

  40. From AS-PATH to AS-SET • Next-hop routing is more amenable to multipath • nodes don’t care about entire paths • … other than for loop detection • Don’t announce routes, announce sets! • set = union of ASes on all routes • BGP route aggregation

  41. Neighbor-SpecificNext-Hop Routing • Customizing route selection for neighbors • operational motivation [Kushman-Kandula-Katabi-Maggs] • economic motivation [Wang-S-Rexford] Secure! R1 C1 ? Short! R2 C2 z d Cheap! R3 C3

  42. Neighbor-SpecificNext-Hop Routing • Neighbor-Specific BGP[Wang-S-Rexford] • implementable using existing tools • Results for convergence and incentive compatibility extend to multipath!

  43. Conclusions andFuture Research • BGP is far too complicated! • New approach: simplify BGP • without compromising global and local goals! • Directions for future research: • getting rid of the AS-PATH? • software / configuration complexity • more theoretical and experimental work

  44. Thank You

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