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15-744: Computer Networking

15-744: Computer Networking. L-7 Software Forwarding. Software-Based Routers. Motivation Enabling innovation in networking research Software data planes Readings: OpenFlow: Enabling Innovation in Campus Networks The Click Modular Router Optional reading

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15-744: Computer Networking

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  1. 15-744: Computer Networking L-7 Software Forwarding

  2. Software-Based Routers • Motivation • Enabling innovation in networking research • Software data planes • Readings: • OpenFlow: Enabling Innovation in Campus Networks • The Click Modular Router • Optional reading • RouteBricks: Exploiting Parallelism To Scale Software Routers

  3. Active Networking Recap • Network API exposes capabilities • Processing, queues, storage • Custom code/functions run on each packet • E.g., conventional IP is best effort, dst based • When could this be insufficient?

  4. Two models of active networks • “Capsule” • Packet carries code! • Programmable router • Operator installs modules on router • Pros/cons?

  5. Criticisms • Too far removed from conventional networks • Upgrade/deployability? • Capsule was considered insecure • No killer apps (continues to be problem) • Performance?

  6. Three logical stages (more hindsight) • Active networking era • Case for “programmable” network devices • “Separation” of control vs data era • Specifically about routing etc • OpenFlow/Network OS era

  7. Network Management Traffic Engineering Performance Security Compliance Resilience

  8. Problem: Toolbox is bad! Traffic Engineering Performance Security Compliance Resilience

  9. Why: Toolbox is implicit in routers! Traffic Engineering Performance Security Compliance Resilience Motivation: Management is complex, expensive, fragile Need: Direct control, expressive policy, network-wide views

  10. Solution • Separate out the “data” and the “control” • Open interface between control/data planes • Logically centralized views • Simplifies optimization/policy management • Network-wide visibility

  11. Today: OpenFlow Controller OpenFlow Config Config

  12. Next Lecture: ONIX Controller E.g., ONIX, NOX, … Config Config

  13. OpenFlow: Motivation • The Internet is a “success disaster” • Many successful applications • Critical for economy as a whole • Too huge a vested infrastructure • Vendors loathe to change anything • Fear in community: “ossification” • New ideas cannot get deployed

  14. Driving questions • Get our own operators comfortable with running network experiments • Isolate experimental traffic from production traffic • What is the functionality that enables innovation?

  15. Rejected alternatives • Get vendors to support • Use PC/Linux based network elements • Existing research prototypes for programmable elements

  16. Their Path • “Pragmatic compromise” • Sacrifice generality for: • Performance • Cost • Vendor “buy-in”

  17. Three Basic Features in OpenFlow Controller Secure Channel Open Protocol Config Config Flow Table

  18. FlowTable Actions • Forward on specific port/interface • Forward to controller (encapsulated) • Drop • Forward legacy • Future support: counters, modifiers

  19. What is nice • Fits well with the TCAM abstraction • Most vendors already have this • They can just expose this without exposing internals

  20. Example Apps • Ethane • Amy’s own OSPF • VLAN • VoIP for Mobile • Support for non-IP

  21. Driving questions: Did it achieve this? • Get operators comfortable with running experimental? • Isolate experimental traffic from production traffic? • What is the functionality that can enable innovation?

  22. Software-Based Routers • Enabling innovation in networking research • Software data planes • Readings: • OpenFlow: Enabling Innovation in Campus Networks • The Click Modular Router • Optional reading • RouteBricks: Exploiting Parallelism To Scale Software Routers

  23. Click overview • Modular architecture • Router = composition of modules • Router = data flow graph • An element is the basic unit of processing • Three key components of each element: • Ports • Configuration • Method interfaces

  24. Simple Tee Element

  25. Two types of “connections” • Push • Source element has finished processing • Sends it downstream • E.g., FromDevice • Pull • Destination is ready to process • Initiates packet transfer • E.g., ToDevice

  26. “Flow” of processing

  27. Click Config File

  28. Click Elements

  29. Other elements • Packet Classification • Scheduling • Queueing • Routing • What you write…

  30. Idea: Polling • Under heavy load, disable the network card’s interrupts • Use polling instead • Ask if there is more work once you’ve done the first batch • Click paper we read – does pure polling

  31. Takeaways • Click is a flexible modular router • Shows that s/w x86 can get pretty good performance • Extensible/modular • Widely used in academia/research • Play with it!

  32. Software-Based Routers • Enabling innovation in networking research • Software data planes • Readings: • OpenFlow: Enabling Innovation in Campus Networks • The Click Modular Router • Optional reading • RouteBricks: Exploiting Parallelism To Scale Software Routers

  33. Buildingrouters • Fast • Programmable • custom statistics • filtering • packet transformation • …

  34. Why programmable routers • New ISP services • intrusion detection, application acceleration • Simpler network monitoring • measure link latency, track down traffic • New protocols • IP traceback, Trajectory Sampling, … Enable flexible, extensible networks

  35. Today: fast or programmable • Fast “hardware” routers • throughput : Tbps • little programmability • Programmable “software” routers • processing by general-purpose CPUs • throughput < 10Gbps

  36. RouteBricks • A router out of off-the-shelf PCs • familiar programming environment • large-volume manufacturing • Can we build a Tbps router out of PCs?

  37. Router = • N: number of external router ports • R: external line rate R R packet processing + switching R R N R R R R

  38. A hardware router • Processing at rate ~R per linecard R R N linecards linecards

  39. A hardware router • Processing at rate ~R per linecard • Switching at rate N x R by switch fabric R R N switch fabric linecards linecards

  40. RouteBricks • Processing at rate ~R per server • Switching at rate ~R per server R R commodity interconnect N servers servers

  41. Outline • Interconnect • Server optimizations • Performance

  42. Requirements • Internal link rates < R • Per-server processing rate: c x R • Per-server fanout: constant R R commodity interconnect N

  43. A naive solution R R R N

  44. A naive solution • N external links of capacity R • N2 internal links of capacity R R R R N

  45. Valiant load balancing (VLB) R/N R R/N R N

  46. Valiant load balancing (VLB) • N external links of capacity R • N2 internal links of capacity R R/N R/N R R N 2R/N

  47. Valiant load balancing (VLB) • Per-server processing rate: 3R • W/ uniform traffic: 2R R/N R/N R R N

  48. Per-server fanout? R N

  49. Per-server fanout? • Increase server capacity R N

  50. Per-server fanout? • Increase server capacity R N

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