rfc4330.Simple Network Time Protocol (SNTP) Versio

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NetworkWorkingGroupD.MillsRequestforComments:4330UniversityofDelawareObsoletes:2030,1769January2006Category:InformationalSimpleNetworkTimeProtocol(SNTP)Version4forIPv4,IPv6andOSIStatusofThisMemoThismemoprovidesinformationfortheInternetcommunity.ItdoesnotspecifyanInternetstandardofanykind.Distributionofthismemoisunlimited.CopyrightNoticeCopyright(C)TheInternetSociety(2006).AbstractThismemorandumdescribestheSimpleNetworkTimeProtocolVersion4(SNTPv4),whichisasubsetoftheNetworkTimeProtocol(NTP)usedtosynchronizecomputerclocksintheInternet.SNTPv4canbeusedwhentheultimateperformanceofafullNTPimplementationbasedonRFC1305isneitherneedednorjustified.WhenoperatingwithcurrentandpreviousNTPandSNTPversions,SNTPv4requiresnochangestothespecificationsorknownimplementations,butratherclarifiescertaindesignfeaturesthatallowoperationinasimple,statelessremote-procedurecall(RPC)modewithaccuracyandreliabilityexpectationssimilartotheUDP/TIMEprotocoldescribedinRFC868.ThismemorandumobsoletesRFC1769,whichdescribesSNTPVersion3(SNTPv3),andRFC2030,whichdescribesSNTPv4.ItspurposeistocorrectcertaininconsistenciesinthepreviousdocumentsandtoclarifyheaderformatsandprotocoloperationsforNTPv3(IPv4)andSNTPv4(IPv4,IPv6,andOSI),whicharealsousedforSNTP.Afurtherpurposeistoprovideguidanceforhomeandbusinessclientimplementationsforroutersandotherconsumerdevicestoprotecttheserverpopulationfromabuse.AworkingknowledgeoftheNTPv3specification,RFC1305,isnotrequiredforanimplementationofSNTP.MillsInformational[Page1]RFC4330SNTPv4forIPv4,IPv6andOSIJanuary2006TableofContents1.Introduction....................................................21.1.SpecificationofRequirements..............................52.OperatingModesandAddressing..................................53.NTPTimestampFormat............................................64.MessageFormat..................................................85.SNTPClientOperations.........................................136.SNTPServerOperations.........................................167.ConfigurationandManagement...................................198.TheKiss-o’-DeathPacket.......................................209.OnBeingaGoodNetworkCitizen................................2110.BestPractices................................................2111.SecurityConsiderations.......................................2412.Acknowledgements..............................................2413.Contributors..................................................2414.InformativeReferences........................................251.IntroductionTheNetworkTimeProtocolVersion3(NTPv3),specifiedinRFC1305[MIL92],iswidelyusedtosynchronizecomputerclocksintheglobalInternet.Itprovidescomprehensivemechanismstoaccessnationaltimeandfrequencydisseminationservices,organizetheNTPsubnetofserversandclients,andadjustthesystemclockineachparticipant.InmostplacesoftheInternetoftoday,NTPprovidesaccuraciesof1-50ms,dependingonthecharacteristicsofthesynchronizationsourceandnetworkpaths.RFC1305specifiestheNTPprotocolmachineintermsofevents,states,transitionfunctionsandactions,andengineeredalgorithmstoimprovethetimekeepingqualityandtomitigateseveralsynchronizationsources,someofwhichmaybefaulty.ToachieveaccuraciesinthelowmillisecondsoverpathsspanningmajorportionsoftheInternet,theseintricatealgorithms,ortheirfunctionalequivalents,arenecessary.Inmanyapplications,accuraciesontheorderofsignificantfractionsofasecondareacceptable.Insimplehomerouterapplications,accuraciesofuptoaminutemaysuffice.Insuchcases,simplerprotocols,suchastheTimeProtocolspecifiedinRFC868[POS83],havebeenusedforthispurpose.TheseprotocolsinvolveanRPCexchangewheretheclientrequeststhetimeofdayandtheserverreturnsitinsecondspastaknownreferenceepoch.NTPisdesignedforusebyclientsandserverswithawiderangeofcapabilitiesandoverawiderangeofnetworkjitterandclockfrequencywandercharacteristics.ManyusersofNTPintheInternetoftodayuseasoftwaredistributionavailablefrom[Page2]RFC4330SNTPv4forIPv4,IPv6andOSIJanuary2006mitigationalgorithms,andsecurityschemes,isarelativelycomplex,real-timeapplication.Althoughthesoftwarehasbeenportedtoawidevarietyofhardwareplatformsrangingfrompersonalcomputerstosupercomputers,itssheersizeandcomplexityisnotappropriateformanyapplications.Accordingly,itisusefultoexplorealternativestrategiesusingsimplersoftwareappropriateforlessstringentaccuracyexpectations.ThismemodescribestheSimpleNetworkTimeProtocolVersion4(SNTPv4),whichisasimplifiedaccessparadigmforserversandclientsusingcurrentandpreviousversionsofNTPandSNTP.TheaccessparadigmisidenticaltotheUDP/TIMEProtocol,and,infact,itshouldbeeasytoadaptaUDP/TIMEclientimplementation,sayforapersonalcomputer,tooperateusingSNTP.Moreover,SNTPisalsodesignedtooperateinadedicatedserverconfigurationincludinganintegratedradioclock.Withcarefuldesignandcontrolofthevariouslatenciesinthesystem,whichispracticalinadedicateddesign,itispossibletodelivertimeaccurateontheorderofmicroseconds.Theonlysignificantprotocolch

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