fast and efficient flow and loss measurement for data...

FastandEfficientFlowandLossMeasurementforDataCenterNetworks

YuliangLiRui Miao Changhoon Kim Minlan Yu

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FlowRadar:Captureallflowsonafinetimescale

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Flowcoverage

• Weneedtoinspecteachindividualflow– Definedby5tuples:source,dest IPs,ports,protocol

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Transientloops/blackholes Fine-grainedtrafficanalysis

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10%

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1 10 100 1000 10000

Distrib

ution

Size (Byte)

Temporalcoverage

• Weneedflowinformationonafinetimescale

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0

1

2

3

4

5

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0 50 100

#Loss

Time (ms)

ShorttimescaleLossrates Timelyattackdetection

DoS

Key insight: division of labor

• Goal:Monitoralltheflowsonafinetimescale

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Overhead atthecollector

Overhead at theswitches

NetFlow

Mirroring

Limitedper-packetprocessingtimeLimitedmemory(10sofMB)

Collectorhaslimitedbandwidthandstorage

Needssampling

Key insight: division of labor

• Goal:Monitoralltheflowsonafinetimescale

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FlowRadar

Usefixedoperationsperpacketatswitches


Overhead at theswitches

NetFlow

Mirroring

Smalldatastructures

FlowRadar architecture

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Extractper-flowcountersacrossswitchesCollector

Switches

AnalysisApplications

Flows&counters

Compactflowcounterswithfixedper-packetoperations

Periodicreport

Challenge:Howtohandlecollisions?

• Handling hashcollisionsishard• Large hash tablesà highmemoryusage• Linked list/Cuckoohashingàmultiple,non-constant#memoryaccesses

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Flow a b cPacketCount … … …

Flowd

d1

collision

Solution:Embracescollisions

• Handling hashcollisionsishard• Large hash tablesà highmemoryusage• Linked list/Cuckoohashingàmultiple,non-constant#memoryaccesses

• Embracingthecollisions• Lessmemoryandconstant#memoryaccesses

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FlowXorFlowCountPacketCount

Solution:Embracescollisions

• Embracingthecollisions:xor upalltheflows• Lessmemoryandconstant#memoryaccesses

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Countingtable

flowa:S(a) Flowb:S(b) Flowc:S(c)a a b b c c

[InvertibleBloomLookupTable(arXiv 2011)]

S(x):#packetsinx

H1 H2 H3

⊕ba a1S(a)

1S(a)

a1S(a)

b1

S(b)+S(b) +S(c)

⊕c b⊕c1

S(b)+S(c)

c1S(c)

2 2 2

FlowFiltertoidentifynewflows

• 1.Checkandupdatetheflowfilter• 2.Updatecountingtable– Thefirstpacketfromanewflow,updateallfields– SubsequentpacketsupdateonlyPacketCount

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bloomfilter:identifynewflow

FlowXor a a⊕b b⊕c b⊕c a cFlowCount 1 2 2 2 1 1PacketCount S(a) S(a)+S(b) S(b)+S(c) S(b)+S(c) S(a) S(c)

+1+1 +1

d

⊕d⊕d ⊕d+1+1 +1

+1+1 +1

d

Flowfilter

[InvertibleBloomLookupTable(arXiv 2011)]

EncodedFlowset

Countingtable

H1 H2 H3

Easytoimplementinmerchantsilicon

• Switchdataplane– Fixedoperations per packet– Smallmemory: 2.36MBfor100Kflows

• Switchcontrolplane– Collectsthesmallencodedflowset every 10ms

• WeimplementeditusingP4Language.– Portabletomanyp4-compatibleswitchchips

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Flows&counters

Extractper-flowcountersacrossswitches



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Compactflowcounterswithfixedper-packetoperations

Collector

Switches

Periodicreport

Encodedflowset

Encodedflowset

Encodedflowset

Stage1.SingleDecode Stage2.Network-wideDecode

Stage1.SingleDecode

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FlowXor …FlowCount …PacketCount …

Bloomfilter

Countingtable

FlowfilterFlow #packeta S(a)… …

Input:anencodedflowset fromasingleswitch

Output:per-flowcounters

Flowfilter

Flow #packeta 5

FlowXor a a⊕b b⊕c⊕d b⊕c⊕d a c⊕dFlowCount 1 2 3 3 1 2PacketCount 5 12 13 13 5 6

Stage1.SingleDecode

• Findapurecell:acellwithoneflow• Removetheflowfromallcells

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Purecell

Decoded:

-1 -1 -1-5 -5 -5

H1 H2 H3

FlowXor 0 b b⊕c⊕d b⊕c⊕d 0 c⊕dFlowCount 0 1 3 3 0 2PacketCount 0 7 13 13 0 6

Flowfilter

Stage1.SingleDecode

• Findapurecell:acellwithoneflow• Removetheflowfromallcells– Createmorepurecells

• Iterateuntilnopurecells

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Flow #packeta 5Decoded:

H1 H2 H3

Stage1.SingleDecode

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FlowXor 0 0 c⊕d c⊕d 0 c⊕dFlowCount 0 0 2 2 0 2PacketCount 0 0 6 6 0 6

Flowfilter

Flow #packeta 5b 7

Decoded:

H1 H2 H3

Flows&counters


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Collector

Switches


Periodicreport

Encodedflowset

Encodedflowset

Encodedflowset


Keyinsight:overlappingsetsofflows

• Thesetsofflowsoverlapacrosshops–Wecanusetheredundancytodecodemoreflows

• Usedifferenthashfunctionsacrosshops

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abcd

abcd

a a⊕c⊕d

b⊕c⊕d

a⊕b⊕c b⊕d

1 3 3 3 2

a⊕d a⊕c b⊕c⊕d

a⊕b⊕c b⊕d

2 2 3 3 2

FlowXor

FlowCountPktCount

FlowXor

FlowCountPktCount

Use5cellstodecode4flows10

Collectorcanleverageflowsets fromallswitchestodecodemoreflows

Keyinsight:overlappingsetsofflows

• Thesetsofflowsoverlapacrosshops–Wecanusetheredundancytodecodemoreflows

• Usedifferenthashfunctionsacrosshops• Provisionswitchmemorybasedonavg(#flows),notmax(#flows)– SingleDecode fornormalcases– Network-widedecodeforburstsofflows

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Challenge1:setsofflowsnotfullyoverlapped

• Flowsfromoneswitchmaygotodifferentnexthops• Oneswitchreceivesflows frommultiplehops

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abcd

a

e

cd

Solution:ZigzagdecodewithFlowFilters

• Generalizetotheentirenetwork– Noneedforroutinginformation– Supportincrementaldeployment

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Flowfilter Flowfilter

a

a b c d

Decoded:

a ec d

ab cc d d eSingleDecode SingleDecodeRemovefromtheother

FlowDecode

Challenge2:differentcountervalues

• Thecounters ofthesameflowmaybedifferentacrosshops– Somepacketsmaygetlost– Somepacketsmaybeonthefly

23drop

Solution:calculatecountersforeachswitch

• Solvealinearequationsystemforeachswitch– Alreadyknowthefullsetofflowsateachswitch– Solvablewithnflowsand>=ncombinationsofcounters

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a b c d

a⊕b⊕d …

3 …14 …

FlowXor

FlowCountPktCount

Flow #pkta 5b 7c 4d 2

!𝑆(𝑎)+𝑆(𝑏)+𝑆(𝑑)=14…

Solving the linearequationsystem

• Challenge:solvingthelinearequationsystemis notfast• Thematrixisverysparse,eachcolumnhask“1”s.• We use iterative solvers• Speeduptheiteration:– Starttheiterationfromcloseapproximationsofcounters,whichisgotfromtheFlowDecode

– Stoptheiterationwhentheresultisfloatingwithin±0.5aninteger.

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Flows&counters


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Collector

Switches


Periodicreport

Encodedflowset

Encodedflowset

Encodedflowset

Stage2.1FlowDecode

Stage2.2CounterDecode


Flow filter

Flow filter

Flow #pktabc

CounterDecode

Flow #pkta 5b 7c 4

FlowDecode

CounterDecode


Flow #pktxyz

Flow #pktx 3y 5z 6


Evaluations

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AnalysisApplicationsFlows&countersCollector

Switches

Stage1.SingleDecode

Stage2.1FlowDecode

Stage2.2CounterDecode

Periodicreport

Encodedflowset

Encodedflowset

Encodedflowset

• Memoryusageisefficient• Bandwidthusageislow• NetDecode vsSingleDecode

Evaluation

• Simulationofk=8FatTree (80switches,128hosts)inns3• Configurethememorybaseonavg(#flow),– whenburstofflowshappens,usenetwork-widedecode

• Theworstcaseisallswitchesarepushedtomax(#flow)– Traffic:eachswitchhassamenumberofflows,andthussamememory

• Eachswitchreportstheflowsets every10ms.

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Memoryefficiency

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#cell=#flow(Impractical) FlowRadar:2.36MB

FlowRadar:24.8MB

Bandwidthusage

• EvaluatedbasedonFacebookdatacenters(SIGCOMM’ 15)– EachToR haslessthan100Kflowsper10msà lessthan2.3Gbps– EachToR talksto44*10G-hosts– FlowRadar consumes0.52%oftotalToR bandwidth

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NetDecode vs. SingleDecode

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SingleDecode NetDecode

SingleDecode:100Kflow,10ms

NetDecodeneedsmoretime

NetDecode:126.8Kflow,3sec

NetDecode

• TheCounterDecode takesthemajorityofthedecodingtime• TheCounterDecode limitsthe#counterscouldbedecoded– If#flows>126.8K,wecanstilldecodeallflows(upto152K)withoutcountersusingFlowDecode

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AnalysisApplicationsFlows&counters

FlowRadar analyzer

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Collector

Switches


Periodicreport

Encodedflowset

Encodedflowset

Encodedflowset

Analysisapplications

• Flowcoverage– Transientloops/blackholes– Errorinmatch-actiontable– Fine-grainedtrafficanalysis

• Temporalcoverage– Shorttimescaleper-flowlossrate– ECMPloadimbalance– Timelyattackdetection

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Per-flowlossmap:bettertemporalcoverage

• Detectlossesaftereveryflowlet

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012345

012345

1 2 3 4 5 6 7 8 9 10 11

Switch1

Switch2

15packets

14packets

35packets

34packets

NetFlowdetectsloss

FlowRadardetectsloss

FlowRadar conclusion

• Reportallper-flowcountersonafinetimescale• Fullyleveragebothswitchesandthecollector– Switches:Encodedflowsets withfixedper-packetprocessingtime,andlowmemoryusage

– Collector:Network-widedecoding

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FlowRadar


Overhead at switches

NetFlow

Mirroring

LossRadar:Detectindividuallossesonafinetimescale

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Losseshavesignificantimpact

• Significantlatencyincreaseandthroughputdrop– ViolatingSLAanddroprevenue

• Takesoperatorsuptotensofhourstofindandfixtheproblem

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Takeaway:WewanttoknowlossASAP

Challenge:manytypesoflosses

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OutputPort 1OutputPortn

InputPort1InputPortn

Input buffer

… parser Ingressmatch-actions(L2->L3->ACL)

Sharedbuffer

Egressmatch-actions

…

SwitchCPU

Configure

corruptions

misconfigurations updates

ResourceshortageResourceshortage corruptions

Greyfailure

Takeaway:Weneedagenerictool

Challenge: losses could happen everywhere

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TCP:I have losses

But I don’t knowwhere

ECMP:multiplepossible paths

Takeaway:Weneedthelocationsofthelosses

Challenge:lackofdetailsoflosses

• Difficulttoinfertherootcauses

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Flow1

Flow2 Pass

Drop

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#Loss

Time (ms)

Differentflowsexperiencedifferentlosspatterns

Losspatternschangeovertime

Takeaway:Needtheinformationofindividuallosses

LossRadar overview

• Fastdetectionà Periodicallysendtrafficdigesttocollector• Knowinglocationà Install meters to monitor traffic• Needinfoofindividuallossesà Includedetailsofeachloss• Beinggenericà Comparethesetsofpackets

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DigestCollector

TrafficDigest

TrafficDigest

TrafficDigest

Howtocoverthewholenetwork

• Need to coverallpipelines

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UM

DMUM

DM

DMUMIngresspipeline

sharedbuffer

Egresspipeline

Cover ingress pipeline Cover egress pipeline

UM:UpstreammeterDM:Downstreammeter

S2

S1S3

LossRadar overview

• Fastdetectionà Periodicallysendtrafficdigesttocollector• Knowinglocationà Install meters to monitor traffic• Needinfoofindividuallossesà Includedetailsofeachloss• Beinggenericà Comparethesetsofpackets

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DigestCollector

TrafficDigest

TrafficDigest

TrafficDigest

Howtocomparethesetsofpackets

• UsingInvertibleBloomFilter(IBF)[Sigcomm’11]• OnlyO(#loss)memory– Eachendkeepsasmallpieceofmemory– Same packetsat both ends will cancel out– Only the differences remain

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upstream

downstream

Collector

How to achieve low memory usage

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xorSumcount

00

00

00

00

00

xorSumcount

00

00

00

00

00

upstream

downstream

Collector


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a a axorSumcount

a1

00

a1

a1

00

xorSumcount

00

00

00

00

00

upstream

downstream

Collector

a

drop

a=5-tuple+IPID


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bb

bxorSumcount

a1

b1

a⊕b2

a1

b1

xorSumcount

00

b1

b1

00

b1

a a a upstream

downstream

Collector

b

bb b b


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c c cupstream

downstream

Collector

xorSumcount

a⊕c2

b⊕c2

a⊕b2

a⊕c2

b1

xorSumcount

00

b1

b1

00

b1

bb

ba a a

b b b

c

drop


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d dd

upstream

downstream

Collector

xorSumcount

a⊕c⊕d3

b⊕c2

a⊕b⊕d3

a⊕c2

b⊕d2

xorSumcount

d1

b1

b⊕d2

00

b⊕d2

c c cb

bba a a

b b bdd d

d

d

xorSumcount

a⊕c2

c1

a1

a⊕c2

00

ca a ac

c

Collectordoessubtraction

Benefits

• Memory-efficient– Proportionalto#losses– 10KBpermeter(trafficpatternreportedinDCTCP)

• Extend to collect more packet information– TTL:helpidentifyloops– Timestamp:taggedinthepacketheadersattheupstream– Anyotherfieldsthatprogrammableswitchescanconfigure

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Challenges

• HowtoensureUMandDMcapturethesamesetofpackets– UsethepacketheadertocarrybatchID

• Incrementaldeployment– Put UMandDMaroundtheblackbox– Comparesum(UMi)andsum(DMj)

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LossRadar conclusion

• Designafastandefficientlossdetectionsystem– Providelocationsanddetailsofindividuallosses– Generictoanytypesoflosses– Memoryonlyproportionalto#losses

• Futurework:designananalyzertodiagnoseproblems– Temporalanalysis,correlationacrossflowsandswitches– Combinewithinfoprovidedbyhosts

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Conclusion

• FullvisibilityofDataCenters– Reportalltheflowsandallthelostpacketsinafewmillisecondsacrossalltheswitches

• Efficientdatastructuresonprogrammableswitches– BothFlowRadar andLossRadar areimplementedonP4– TechnologytransfertoBarefootswitches(Seemydemotomorrow)

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fast and efficient flow and loss measurement for data...

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