ISP ColumnJanuary docWord文件下载.docx
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ISP ColumnJanuary docWord文件下载.docx
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CommentsSubmittedby
GeoffHuston,
ResearchScientist,AsiaPacificNetworkInformationCentre
ThesecommentsareintendedtoaddresstheissuesraisedinSectionIIA,regardingestimatesofhowmanyIPv4addresshavebeenallocated,howmanyarestillavailable,andhowlongtheremainingaddressspacewillcontinuetomeettheneedsofusersintheUnitedStates,aswellasusersinothercountriesaroundtheworld.
TheRequestforCommentcitesinafootnoteapresentationImadetotheAPNICOpenPolicyMeetinginAugust2003.Iwouldliketosubmitthefollowingcommentaryasanexplanationofthemethodologyused,aswellasprovidinganupdateontheprojectionsofIPv4consumptionincorporatingdatauptotheendofFebruary2004.
Summary
ThisstudyexaminestheavailabledataconcerningtheconsumptionofIPv4addresses,lookingattheallocationdatapublishedbytheInternetAssignedNumbersAuthority(IANA),theallocationdatapublishedbytheRegionalInternetRegistries(RIRs)andtheaddressspanencompassedbyadvertisementswithintheInternetglobalroutingsystem.
Thestudyexaminesthetrendsofconsumptionsinceandexamineswhetherthecurrentconsumptiontrendsarebestmodeledusinganexponentialoralineargrowthtrend.Thestudyconcludesthatthebestmodelofthecurrentconsumptionratesofaddressspacecanbefoundinananalysisoftheglobalroutingtable,andthebestfitmodelisthatoflineargrowth.
ItconcludesthattheIPv4world,intermsofaddressavailability,couldcontinueupto2030withoutreachinganyfixedboundaryofaddressexhaustion.However,informingthismodelanumberofrelativelysweepingassumptionshavebeenmade,andtocombinethemasisdonehereispushingthepredictiveexercisetoitslimits,orpossiblybeyondthem.ThreedecadesoutiswayovertheeventhorizonforanyformofusefulpredictionfortheInternetIfthequestionisrestrictedtothenextdecade(i.e.upto2014),thenwecananswerwithsomelevelofconfidencethatthereisreallynovisibleevidenceofIPv4exhaustingitsaddresspoolbasedontheavailableaddressconsumptiondata.
TheconclusiondrawnhereisthatiftheprimedriverfortheadoptionofIPv6liesinaloomingshortageofpublicIPv4addresses,thenthisisnotaneartermprospect,andanyimpetusfortheadoptionforIPv6wouldneedtobebasedonfactorsotherthananimminentexhaustionofIPv4addressspace.
Introduction
TheIPv4addresspoolisoffinitesize,and,astheIPv4Internetgrowsitmakescontinualdemandsonpreviouslyunallocatedaddressspace.Itispossibletoposethequestionof"
HowlongcantheIPv4addresspoollastinthefaceofacontinualgrowthinthedemandforaddresses?
"
ThissubmissionlooksatoneapproachtoattempttoprovidesomeindicationofwhentheIPv4addresspoolislikelytobeexhaustedasaconsequenceofthiscontinueddemandforaddresses,anddescribesthevariousassumptionsthathavebeenmadeinordertomakethisprediction.
PredictionsofAddressConsumption
PredictingthepointofIPv4addressexhaustionwasfirstundertakenwithintheIETFintheearly1990saspartofanexerciseinlookingatthefuturerequirementsoftheInternetintermsofbothaddressspaceandroutingcapabilities.TheinitialoutcomesoftheconsequentIETFactivitiestoalleviatethepressureontheaddresspoolwereclearlyvisiblebythemid-1990'
s:
theClasslessaddressarchitecture(ClasslessInter-DomainRouting,or“CIDR”)wasveryeffectiveinimprovingtheaddressutilizationefficiency,andthepressuresofever-increasingconsumptionofavisiblyfiniteaddressresourcewerealleviated.TheIETFactionstoaddressthelongertermrequirementsofaddressspacewasofcourseIPv6.
DistributingtheAddressSpace
Therearethreestagesinaddressdistribution.ThepoolofIPaddressesismanagedbytheInternetAssignedNumbersAuthority(IANA).BlocksofaddressspacehavebeendefinedthroughstandardsactionsoftheIETFforuseasglobalunicastaddresses,private-useunicastaddresses,multicastaddresses,reservedforfutureactions,andotherblocksaremarkedasreserved,andarenottobeusedoutsideoflocalhostcontexts.
Currentlythereare3,707,764,736addressesthataremanagedasglobalunicastaddresses.Itisprobablyeasiertolookatthisintermsofthenumberof"
/8blocks"
whereeachblockisthesamesizeastheoldClassAnetwork,namely16,777,216addresses.Thetotalglobalunicastaddresspoolis221/8s,withafurther16/8sreservedformulticastuse,16/8sheldinreserve,and3/8saredesignatedasnotforuseinthepublicInternet.(Figure1)
Figure1–BreakdownofIPv4addressspace
TheprocessofaddressmanagementisthattheIETFdefinestheglobalunicastaddresspooltotheIANA.IANAallocatesblocksofglobalunicastaddressestoRegionalInternetRegistries(RIRs).TheRIRsallocateaddressblockstoLocalInternetRegistries(LIRs)orInternetServiceProviders(ISPs).TheseaddressblocksarethenadvertisedintheInternet’sBorderGatewayProtocol(BGP)routingtable(Figure2).
Figure2–AddressDistributionFramework
Inlookingatfuturestherearethreedistinctquestionsconcerningaddressconsumption:
∙HowquicklyistheIANApassingaddressblockstotheRIRs,andwhenwillIANArunout?
∙HowquicklyaretheRIRspassingaddressblockstoLIRs,andwhenwillthisrunout?
∙HowmuchaddressspaceisactuallyusedintheglobalInternet,andhowquicklyisthisgrowing?
Therelatedquestioniswhenwilldemandforaddressesoutstriptheavailableaddresspool?
TheIANARegistry
ThefirstdatasettoexamineistheIANAregistryfile.Thisregistryindicatesthatofthese221/8blocks86/8blocksarestillheldasunallocatedbytheIANA,133.9/8blockshavebeenallocated.(Figure3).
Figure3–AddressPoolwithRIRAllocations
TheIANAregistryalsoincludesthedateofallocationoftheaddressblock,soit’spossibletoconstructatimeseriesofIANAallocations.(Figure4)
Figure4-TimeSeriesofIANAAllocations
Interestingly,thereisnothingolderthan1991inthisregistry.Thisexposesoneoftheproblemswithanalyzingregistrydata,inthatthereisadifferencebetweenthecurrentstatusofaregistry,andatime-stampedlogofthetransactionsthatweremadetotheregistryovertime.ThedatapublishedbytheIANAissomewherebetweenthetwo.Thelogofdataisincomplete,andthecurrentstatusofsomeaddressblocksisunclear.Itappearsthatreliableallocationdatastartsin1995.Soifwetakethedatastartingfrom1995andperformalinearregressiontofindabestfitofanexponentialprojection,itspossibletomakesomepredictionsastothetimeitwilltaketoexhausttheremainingunallocated89/8s.(Figure5).
Figure5-ProjectionofIANAAllocations
Itisworthaslightdigressionintothemethodofprojectionbeingusedhere.Thetechniqueisoneofusingaleastsquarestechniquetofindabestfitofanexponentialgrowthcurvetothedata.Theunderlyingassumptionbehindsuchexponentialprojectionsisthatthegrowthrateofthedataisproportionaltothesizeofthedata,ratherthanbeingaconstantrate.Innetworkterms,thisassumesthattherateofconsumptionofunallocatedaddressesissomeconstantproportionofthenumberofallocatedaddresses,or,inotherwords,theexpansionrateofthenetworkisaproportionofitssize,ratherthanbeingaconstantvalue.Suchexponentialgrowthmodelsmaynotnecessarilybethebestfittoanetworkgrowthmodel,althoughthedatasince1995doesappeartocorrelatereasonablytoanunderlyingexponentialgrowthpattern.Whetherthisgrowthmodelwillcontinueintothefutureisanopenissue.Itisalsopossibletofitalineargrowthmodeltothedata,inwhichcasetheprojectedexhaustionpointshiftsfrom2019to2027.
Theprojectionof2019asthedateforexhaustionoftheIANAunallocatedaddressspacepoolusingthisexponentialgrowthmodelisperhapssurprising,asitsseemsthatthenetworkisbiggernowthanever,yettheamountofadditionaladdressspacerequiredtofuelfurtheracceleratinggrowthforafurtherdecadeiscomparativelysmall.
Thereareanumberofreasonswhythisisthecase,andtheturningpointwhentheseaspectsgainedtractionintheInternetappearedtobearound1995.Theyinclude:
∙Thefirst1.6billionaddresses(equivalenttosome100/8blocks)wereallocatedusingtheClass-basedaddressarchitecture.Sincethisdateaddressallocationhasusedaclasslessarchitecture,andthishasallowedforsignificantlyimprovedefficienciestobeachievedinusingtheaddressspace.
∙TheRegionalInternetRegistries(RIRs)assumedresponsibilityforaddressallocation,andstartedusingconservation-basedpoliciesindeterminingallocations.TheRIRprocessrequireseachaddressapplicanttodemonstratethattheycanmakeefficientandeffectiveuseoftheaddressspace,andthisdampenedsomeofthewildersetsofexpectationsaboutanenterprise’saddressrequirements.
∙AddressCompressiontechnologiesbecamewidelydeployed.DynamicNetworkAddressTranslationdevices(NATs)have,forbetterorworse,becomeacommonpartofthenetworklandscape.NATsallowlarge'
semi-private'
networkstouseaverysmallpollofpublicaddressesastheexternalviewofthenetwork,whileusingprivateaddressspacewithinthenetwork.DynamicHostConfigurationProtocol(DHCP)hasallowednetworkstorecycleasmallerpoolofaddressesacrossalargersetofintermittently-con
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