VROOM: Virtual ROuters On the Move

VROOM: Virtual ROuters On the Move

Aditya Akella

Based on slides from Yi Wang

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

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VROOM: The Basic Idea • Virtual routers (VRs) form logical topology

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2 3

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physical router

virtual router

logical link

VROOM: The Basic Idea • VR migration does not affect the logical topology

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2 3

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physical router

virtual router

logical link

Outline

• 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!

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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

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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

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Case 1: Planned Maintenance• Today’s best practice: “cost-out/cost-in”

– Router reconfiguration & protocol reconvergence

• VROOM– NO reconfiguration of VRs, NO reconvergence

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PR-A

PR-B

VR-1




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PR-A

PR-B

VR-1




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PR-A

PR-B

VR-1

Case 2: Service Deployment & Evolution

• Deploy a new service in a controlled “test network” first

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Production network

Test network

Test network

Test network

CECECE

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

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Production network

Test network

Test network

Test network

Case 3: Power Savings

• Big power consumption of routers– Millions of Routers in the U.S.– Electricity bill: $ hundreds of millions/year

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(Source: National Technical Information Service, Department of Commerce, 2000. Figures for 2005 & 2010 are projections.)

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2.4

3.9

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2000 2005 2010

TwH/year


• Observation: the diurnal traffic pattern• Idea: contract and expand the physical

network according to the traffic demand

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Dynamically contract & expand the physical network in a day - 3PM


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Dynamically contract & expand the physical network in a day - 9PM


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Dynamically contract & expand the physical network in a day - 4AM

• 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

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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?

VROOM Architecture

• Three enablers that make VR migration possible– Router virtualization– Control and data plane separation– Dynamic interface binding

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A Naive Migration Process

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1. Freeze the virtual router2. Copy states3. Restart4. Migrate links

Practically unacceptable Packet forwarding should not stop during migration

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VROOM’s Migration Process Key idea: separate the migration of control and data plane

No data-plane interruption Low control-plane interruption

1. Control-plane migration2. Data-plane cloning3. Link migration

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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”)

t1 t2 t3 t4time

1 2

1: router-image copy

2: memory copy

pre-copy stall-and-copy

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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

t1 t2 t3 t4time

1 2


2: memory copy

t5

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3: data-plane cloning

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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

t1 t2 t3 t4time

1 2


2: memory copy

t5

3


old nodenew node

control plane

remote control plane

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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.

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Double Data Planes At the end of data-plane cloning, two data planes are ready to

forward traffic (i.e., “double data planes”)

t1 t2 t3 t4time

1 2


2: memory copy

t5

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t0

0

0: tunnel setupdoubledata plane

data plane

old node

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4: asynchronous link migration

new node

old nodenew node

control plane

remote control planet6

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Asynchronous Link Migration With the double data planes, each link can be migrated

independently Eliminate the need for a synchronization system

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?

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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)

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

dropped

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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”

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Dynamic Interface Binding bindd provides two types of bindings:

Map substrate interfaces to the right FIB Map substrate interfaces to the right virtual

interfaces

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Putting It Altogether: Realizing Migration

1. The migration program notifies shadowd about the completion of the control plane migration

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2. shadowd requests zebra to resend all the routes, and pushes them down to virtd

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3. virtd installs routes the new FIB, while continuing to update the old FIB

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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

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Evaluation

Answer three questions Performance of individual migration steps? Impact on data traffic? Impact on routing protocol?

Experiments on Emulab

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Performance of Migration Steps

Memory copy time With different

numbers of routes (dump file sizes)

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0 10k 100k 200k 300k 400k 500k

Number of routes

Time (seconds)

Suspend + dump Copy dump file Undump + resume Bridging setup

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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

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Data Plane Impact

The diamond testbed

64-byte UDP packets, round-trip traffic

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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

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The Importance of Separate Migration Bandwidth

The dumbbell testbed

250k routes in the RIB

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Separate Migration Bandwidth is Important

Throughput of the migration traffic

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Delay increase of the data traffic

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Loss rate of the data traffic

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Control Plane Impact

The Abilene testbed

Assume a backbone running MPLS VR5 configured as

Core router (running OSPF only) Edge router (running OSPF + BGP)

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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

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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)

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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

Outline

• Why is VROOM a good idea?• What are the challenges?• How does VROOM work?• Is VROOM practical?• Where to migrate?

Deciding Where To Migrate• Physical constraints

– Latency• E.g, NYC to Washington D.C.: 2 msec

– Link capacity• Enough remaining capacity for extra traffic

– Platform compatibility• Routers from different vendors

– Router capability• E.g., number of access control lists (ACLs) supported

• Good news: these constraints limit the search space

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Two Optimization Problems

• For planned maintenance/service deployment– Minimize path stretch– With constraints on link capacity, platform

compatibility, router capability, etc.

• For power savings– Maximize power savings

• With different regional electricity prices

– With constraints on path stretch, link capacity, etc.

Conclusions

• VROOM offers a useful network-management primitive– separates the tight coupling between physical and logical– Simplify network management, enable new applications

• Live router migration with minimal disruption– Data-plane hypervisor enables

• Data-plane cloning• Remote control plane• Double data plane and asynchronous link migration

– No data-plane disruption– No visible control-plane disruption

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VROOM: Virtual ROuters On the Move

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