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  1. VROOM: Virtual ROuters On the Move Yi Wang (Princeton) With: Eric Keller (Princeton) Brian Biskeborn (Princeton) Kobus van der Merwe (AT&T Labs - Research) Jennifer Rexford (Princeton)

  2. Virtual ROuters On the Move (VROOM) • Key idea • Routers should be free to roam around • Useful for many different applications • Simplify network maintenance • Simplify service deployment and evolution • Reduce power consumption • … • Feasible in practice • No performance impact on data traffic • No visible impact on routing protocols

  3. VROOM: The Basic Idea • Virtual routers (VRs) form logical topology 1 4 3 2 physical router 5 virtual router logical link

  4. VROOM: The Basic Idea • VR migration does not affect the logical topology 2 physical router 3 virtual router 1 logical link 4 5

  5. The Rest of the Talk is Q&A • Why is VROOM a good idea? • What are the challenges? • Or it is just technically trivial? • How does VROOM work? • The migration process • Is VROOM practical? • Prototype system • Performance evaluation • Where to migrate? • The scheduling problem • Still have questions? Feel free to ask! 5

  6. The Coupling of Logical and Physical • Today, the physical and logical configurations of a router is tightly coupled • Physical changes break protocol adjacencies, disrupt traffic • Logical configuration as a tool to reduce the disruption • E.g., the “cost-out/cost-in” of IGP link weights • Cannot eliminate the disruption • Account for over 73% of network maintenance events

  7. VROOM Separates the Logical and Physical • Make a logical router instance migratable among physical nodes • All logical configurations/states remain the same before/after the migration • IP addresses remain the same • Routing protocol configurations remain the same • Routing-protocol adjacencies stay up • No protocol (BGP/IGP) reconvergence • Network topology stays intact • No disruption to data traffic

  8. Case 1: Planned Maintenance • Today’s best practice: “cost-out/cost-in” • Router reconfiguration & protocol reconvergence • VROOM • NO reconfiguration of VRs, NO reconvergence VR-1 PR-A PR-B

  9. Case 1: Planned Maintenance • Today’s best practice: “cost-out/cost-in” • Router reconfiguration & protocol reconvergence • VROOM • NO reconfiguration of VRs, NO reconvergence VR-1 PR-A PR-B

  10. Case 1: Planned Maintenance • Today’s best practice: “cost-out/cost-in” • Router reconfiguration & protocol reconvergence • VROOM • NO reconfiguration of VRs, NO reconvergence VR-1 PR-A PR-B

  11. Case 2: Service Deployment & Evolution • Deploy a new service in a controlled “test network” first CE CE CE Test network Test network Production network Test network

  12. Case 2: Service Deployment & Evolution • Roll out the service to the production network after it matures • VROOM guarantees seamless service to existing customers during the roll-out and later evolution Test network Test network Production network Test network

  13. Case 3: Power Savings • Big power consumption of routers • Millions of Routers in the U.S. • Electricity bill: $ hundreds of millions/year (Source: National Technical Information Service, Department of Commerce, 2000. Figures for 2005 & 2010 are projections.)

  14. Case 3: Power Savings • Observation: the diurnal traffic pattern • Idea: contract and expand the physical network according to the traffic demand

  15. Case 3: Power Savings Dynamically contract & expand the physical network in a day - 3PM

  16. Case 3: Power Savings Dynamically contract & expand the physical network in a day - 9PM

  17. Case 3: Power Savings Dynamically contract & expand the physical network in a day - 4AM

  18. Migrate an entire virtual router instance All control plane & data plane processes / states Minimize disruption Data plane: up to millions packets per second Control plane: less stringent (w/ routing message retrans.) Migrate links Virtual Router Migration: the Challenges 18

  19. Outline • Why is VROOM a good idea? • What are the challenges? • How does VROOM work? • The migration enablers • The migration process • What to be migrated? • How? (in order to minimize disruption) • Is VROOM practical? • Where to migrate?

  20. VROOM Architecture • Three enablers that make VR migration possible • Router virtualization • Control and data plane separation • Dynamic interface binding

  21. A Naive Migration Process • Freeze the virtual router • Copy states • Restart • Migrate links • Practically unacceptable • Packet forwarding should not stop during migration

  22. VROOM’s Migration Process • Key idea: separate the migration of control and data plane • No data-plane interruption • Low control-plane interruption • Control-plane migration • Data-plane cloning • Link migration 22

  23. Control-Plane Migration • Two things to be copied • Router image • Binaries, configuration files, etc. • Memory • 1st stage: pre-copy • 2nd stage: stall-and-copy (when the control plane is “frozen”) 2 1 time t1 t2 t3 t4 pre-copy stall-and-copy 1: router-image copy 2: memory copy 23

  24. Data-Plane Cloning • Clone the data plane by repopulation • Copying the data plane states is wasteful, and could be hard • Instead, repopulate the new data plane using the migrated control plane • The old data plane continues working during migration 2 3 1 time t1 t2 t3 t4 t5 1: router-image copy 2: memory copy 3: data-plane cloning 24

  25. Remote Control Plane • The migrated control plane plays two roles • Act as a “remote control plane” for the old data plane • Populate the new data plane 2 3 1 time t1 t2 t3 t4 t5 remote control plane control plane old node new node 1: router-image copy 2: memory copy 3: data-plane cloning 25

  26. Keep the Control Plane “Online” • Data-plane cloning takes time • Around 110 us per FIB entry update (for high-end router) * • Installing 250k routes could take over 20 seconds • The control plane needs connectivity during this period • Redirect the routing messages through tunnels *: P. Francios, et. al., Achieving sub-second IGP convergence in large IP networks, ACM SIGCOMM CCR, no. 3, 2005. 26

  27. Double Data Planes • At the end of data-plane cloning, two data planes are ready to forward traffic (i.e., “double data planes”) 4 2 3 0 1 time t0 t1 t2 t3 t4 t5 t6 remote control plane control plane old node new node old node data plane new node 0: tunnel setup double data plane 1: router-image copy 2: memory copy 3: data-plane cloning 4: asynchronous link migration 27

  28. Asynchronous Link Migration • With the double data planes, each link can be migrated independently • Eliminate the need for a synchronization system 28

  29. Outline • Why is VROOM a good idea? • What are the challenges? • How does VROOM work? • Is VROOM practical? • Prototype system • Performance evaluation • Where to migrate?

  30. Prototype Implementation • PC + OpenVZ • OpenVZ: OS-level virtualization • Lighter-weight • Supports live migration • Two prototypes • Software-based data plane (SD): Linux kernel • Hardware-based data plane (HD): NetFPGA • NetFPGA: 4-port gigabit Ethernet PCI with an FPGA • Why two prototypes? • To validate the data-plane hypervisor design (e.g., migration between SD and HD) 30

  31. The Out-of-box OpenVZ Approach • Packets are forwarded inside each VE • When a VE is being migrated, packets are dropped 31

  32. Control and Data Plane Separation • Move the FIBs out of the VEs • shadowd in each VE, “pushing down” route updates • virtd in VE0, as the “data-plane hypervisor” 32

  33. Dynamic Interface Binding • bindd provides two types of bindings: • Map substrate interfaces to the right FIB • Map substrate interfaces to the right virtual interfaces 33

  34. Putting It Altogether: Realizing Migration 1. The migration program notifies shadowd about the completion of the control plane migration 34

  35. Putting It Altogether: Realizing Migration 2. shadowd requests zebra to resend all the routes, and pushes them down to virtd 35

  36. Putting It Altogether: Realizing Migration 3. virtd installs routes the new FIB, while continuing to update the old FIB 36

  37. Putting It Altogether: Realizing Migration 4. virtd notifies the migration program to start link migration after finishing populating the new FIB 5. After link migration is completed, the migration program notifies virtd to stop updating the old FIB 37

  38. Evaluation • Answer three questions • Performance of individual migration steps? • Impact on data traffic? • Impact on routing protocol? • Experiments on Emulab 38

  39. Performance of Migration Steps • Memory copy time • With different numbers of routes (dump file sizes) 39

  40. Performance of Migration Steps • FIB population time • Grows linearly w.r.t. the number of route entries • Installing a FIB entry into NetFPGA: 7.4 microseconds • Installing a FIB entry into Linux kernel: 1.94 milliseconds • FIB update time: time for virtd to install entries to FIB • Total time: FIB update time + time for shadowd to send routes to virtd 40

  41. Data Plane Impact • The diamond testbed • 64-byte UDP packets, round-trip traffic 41

  42. Data Plane Impact • HD router with separate migration bandwidth • No delay increase or packet loss • SD router with separate migration bandwidth • Up to 3.7% delay increase at 5k packets/s • Less than 0.4% delay increase at 25k packets/s SD, 5k packets/s 42

  43. The Importance of Separate Migration Bandwidth • The dumbbell testbed • 250k routes in the RIB 43

  44. Separate Migration Bandwidth is Important • Throughput of the migration traffic 44

  45. Separate Migration Bandwidth is Important • Delay increase of the data traffic 45

  46. Separate Migration Bandwidth is Important • Loss rate of the data traffic 46

  47. Control Plane Impact • The Abilene testbed • Assume a backbone running MPLS • VR5 configured as • Core router (running OSPF only) • Edge router (running OSPF + BGP) 47

  48. Core Router Migration • No events during migration • Average control plane downtime: 0.972 seconds (0.924 - 1.008 seconds in 10 runs) • Support 1-second OSPF hello-interval (with 4-second dead-interval) • Miss at most one hello message 48

  49. Core Router Migration • Events happen during migration • Introducing events (LSA) by flapping link VR2-VR3 • Miss at most one LSA • Get retransmission 5 seconds later (the default LSA retransmission-interval) • Can use smaller LSA retransmission-interval (e.g., 1 second) 49

  50. Edge Router Migration • 255k BGP routes + OSPF • Dump file size grows from 3.2MB to 76.0MB • Average control plane downtime: 3.560 seconds (3.484 - 3.594 seconds in 10 runs) • Support 2-second OSPF hello-interval (with 8-second dead-interval) • BGP sessions stay up • In practice, ISPs often use the default values • 10-second hello-interval • 40-second dead interval 50