管理才能考核表Title課件

DHCP,DNS,SNMPDebashisSahaMISGroup,IIMCalcuttads@iimcal.ac.in1DHCP,DNS,SNMP1FirstQuestionThursday,May17,20072FirstQuestionThursday,May17TheInternetandAddressingAllmachinesontheInternetareaccessedviatheirIPaddressDottedquad:xxx.xxx.xxx.xxxProblem:IPaddressesarehardtorememberandhardtostaticallyassignonlargenetworksSolution:NeedtocomeupwithawaytoautomaticallyassignIPaddressesandatextbasedrepresentationofmachineaddressesinsteadofjust4numbersThursday,May17,20073TheInternetandAddressingAllAddressingSolutionsTwoprotocolshavebeendevelopedtosolvetheseproblemsDHCP–automaticnetworkconfiguration(includingIPaddress)DNS–translatestextualbasednamesintoIPaddressesandviceversaThursday,May17,20074AddressingSolutionsTwoprotocDHCP–DynamicHostConfigurationProtocolThursday,May17,20075DHCP–DynamicHostConfiguratDHCPAllowsclientmachinestoreceiveanIPaddress,DNSinformation,etcautomaticallyBeforeDHCPcameintouse,usershadtotypeinallthisinformationbyhand,whichisbad:EasytomistypesomethingwhenenteringbyhandManuallychangingnetworkconfigurationeverytimeyoumoveyourlaptopisapainBootpresolvedsomeoftheseissues…andDHCPstillusesthesameportasbootpThursday,May17,20076DHCPAllowsclientmachinestoPurposeofDHCP FromRFC-2131(theInternetstandard):TheDynamicHostConfigurationProtocol(DHCP)providesaframeworkforpassingconfigurationinformationtohostsonaTCP/IPnetwork.DHCPconsistsoftwocomponents:aprotocolfordeliveringhost-specificconfigurationparametersfromaDHCPservertoahostandamechanismforallocationofnetworkaddressestohosts.Thursday,May17,20077PurposeofDHCP FromRFC-2131DHCPfunctionalgoalsAhostwithoutavalidIPaddresslocatesandcommunicateswithaDHCPserverADHCPserverpassesconfigurationparameters,includinganIPaddress,tothehostTheDHCPservermaydynamicallyallocateaddressestohostsandreuseaddressesHostscandetectwhentheyrequireanewIPaddressUnavailabilityofDHCPserverhasminimaleffectonoperationofhostsThursday,May17,20078DHCPfunctionalgoalsAhostwiDHCP:BasicsAclientleasesanIPaddressfromaDHCPserverforagivenamountoftimeWhenleaseexpires,theclientmustaskDHCPserverforanewaddress(clientsattempttorenewleaseafter50%oftheleasetimehasexpired)Typicalleasesmaylastforfrom30secondsto24hours,orevenlonger.Thursday,May17,20079DHCP:BasicsAclientleasesanWhatdoesDHCPdo?Providesprotocolstack,applicationandotherconfigurationparameterstohostsEliminatesneedforindividual,manualconfigurationforhostsIncludesadministrativecontrolsfornetworkadministratorsBackwardcompatiblepacketformatforBOOTPinteroperation(RFC1542)Cancoexistwithhoststhathavepre-assignedIPaddressesandhoststhatdonotparticipateinDHCPThursday,May17,200710WhatdoesDHCPdo?ProvidesproDesignGoalsEliminatemanualconfigurationofhostsPreventuseofanyIPaddressbymorethanonehostShouldnotrequireaserveroneverysubnetAllowformultipleDHCPserversProvideamechanism,notapolicyProvidethesameconfiguration-includingIPaddress-toahostwheneverpossibleThursday,May17,200711DesignGoalsEliminatemanualcWhatcanyoudowithDHCPPlug-and-playMovedesktopPCsbetweenofficesRenumberOtherrestructuring-changesubnetmasksMobileIP-laptopsMovingequipment-cartableThursday,May17,200712WhatcanyoudowithDHCPPlug-WhatDHCPdoesn’tdoSupportmultipleaddressesperinterfaceInformrunninghostthatparametershavechangedPropagatenewaddressestoDNSSupportinter-servercommunicationProvideauthenticatedmessagedeliveryConfigureroutersandothernetworkequipmentDesignnetworkaddressingplanDetermineotherconfigurationparametersLocateotherserversThursday,May17,200713WhatDHCPdoesn’tdoSupportmuDHCP:MessagesOverviewSeveralmessagesaresentbackandforthbetweenaclientandtheDHCPserverbeforeitcansuccessfullyobtainanIPaddressThursday,May17,200714DHCP:MessagesOverviewSeveralDHCP:DISCOVERHardcodingtheaddressesofDHCPserverskindofdefeatsthepurposeofautomaticconfigurationSolution:AclientusingDHCPwillbroadcastaDISCOVERmessagetoallcomputersonitssubnet(addr55)tofigureouttheIPaddressofanyDHCPserversMostroutersareconfiguredtopassthisrequestwithinthecampusorenterpriseThursday,May17,200715DHCP:DISCOVERHardcodingtheaDHCP:OFFER(Optionally)sentfromserverinresponsetoaDISCOVERContainsanIPaddress,otherconfigurationinformationaswell(subnetmask,DNSservers,defaultgateway,searchdomains,etc)NotethatallDHCPserversthatreceiveaDISCOVERrequestmaysendanOFFER;sinceaclienttypicallydoesnotneedmorethanoneIPaddress,moremessagesneededtozeroononeIPThursday,May17,200716DHCP:OFFER(Optionally)sentfDHCP:REQUESTSentbyclienttorequestacertainIPaddressUsuallytheonesentbyanOFFER,butalsousedtorenewleases.AlsocanbesenttotrytogetsameaddressafterarebootThismessageisbroadcastMostOSsbydefaultwillsendaREQUESTforthefirstOFFERtheyreceive–thismeansthatifthereisarogueDHCPserveronyoursubnet,mostclientswillignoretheOFFERsfromthecampusDHCPservers(sincetheOFFERfromtherogueservergetstotheuser’sPCfirst)!Thursday,May17,200717DHCP:REQUESTSentbyclienttoDHCP:ACK/NACKSentbyserverinresponsetoaREQUESTACK:Requestaccepted,clientcanstartusingtheIPitREQUESTedNACK:Somethingiswrongwiththeclient’sREQUEST(forexampletheyrequestedanIPaddressthey’renotsupposedtohave)Thursday,May17,200718DHCP:ACK/NACKSentbyserveriDHCP:RELEASESentbyclienttoendaleaseNotstrictlyrequired,butisthe“polite”thingtodoifdonewiththeIP(couldjustlettheleaseexpire)SomeclientsmaynotsendRELEASEsinanattempttokeepthesameIPaddressforaslongaspossibleThursday,May17,200719DHCP:RELEASESentbyclienttoDHCP:BigPictureThursday,May17,200720DHCP:BigPictureThursday,MaySummaryDHCPworkstodayasatoolforautomaticconfigurationofTCP/IPhostsItisanopenInternetstandardandinteroperableclientimplementationsarewidelyavailableProvidesautomationforroutineconfigurationtasks,oncenetworkarchitecthasconfigurednetworkandaddressingplanOngoingworkwillextendDHCPwithauthentication,DHCP-DNSinteractionandinter-servercommunicationThursday,May17,200721SummaryDHCPworkstodayasatDHCP:ConclusionEfficientwayofassigningcomputersIPaddressesanddeliveringconfigurationinformationtothosecomputersDoesnotsolveotherproblemofaddressing–thatIPaddressesarehardtorememberThursday,May17,200722DHCP:ConclusionEfficientwayIETFstandardsFormalprocessfordevelopment,reviewandacceptanceofTCP/IPprotocolsuitestandardsInitialspecificationspublishedasInternetDrafts(I-Ds)AcceptedspecificationspublishedasRequestforComments(RFCs)Thursday,May17,200723IETFstandardsFormalprocessfProtocolstatusDHCPhasbeenacceptedasaDraftStandard;thespecificationsarepublishedin:RFC2131:DynamicHostConfigurationProtocolRFC2132:DHCPOptionsandBOOTPVendorExtensionsSeveraladditionaloptionsareindevelopmentThursday,May17,200724ProtocolstatusDHCPhasbeenaImplementationstatusDHCPisanopenstandard,withfreelyavailablespecificationsCanbe(andhasbeen)implementedentirelyfromthespecificationCommercialimplementationsarewidelyavailableNon-commericalimplementationsarealsoavailableThursday,May17,200725ImplementationstatusDHCPisaDHCPResourcesThursday,May17,200726DHCPResourcesThursday,May17DNS–DomainNameSystemThursday,May17,200727DNS–DomainNameSystemThursdSecondQuestionThursday,May17,200728SecondQuestionThursday,May1DomainNameSystem(DNS)Thursday,May17,200729DomainNameSystem(DNS)ThursdHostnamesThursday,May17,200730HostnamesThursday,May17,200DNS:BasicsHierarchicalnamespaceDistributedsystem–veryfewcoreserversStoresotherinformationthansimple

hostname<->IPmappingsRequest/responseprotocolThursday,May17,200731DNS:BasicsHierarchicalnamespDNSHierarchyeducomorginrpialbanyaciimcalThursday,May17,200732DNSHierarchyeducomorginrpialbHostnamestructureEachhostnameismadeupofasequenceoflabelsseparatedbyperiods.Eachlabelcanbeupto63charactersThetotalnamecanbeatmost255characters.Examples:

Thursday,May17,200733HostnamestructureEachhostnDomainNameThedomainnameforahostisthesequenceoflabelsthatleadfromthehost(leafnodeinthenamingtree)tothetopoftheworldwidenamingtree.Adomainisasubtreeoftheworldwidenamingtree.Thursday,May17,200734DomainNameThedomainnameforHierarchicalNamingcomedugovmilnetorgusarpacolordaocsfoobarThursday,May17,200735HierarchicalNamingcomedugovmiTopleveldomainsedu,gov,com,net,org,mil,…Countrieseachhaveatopleveldomain(2letterdomainname).Suchas.in,.uk,.it,etc.Newtopleveldomainsinclude:.Thursday,May17,200736Topleveldomainsedu,gov,comDomainNamingSystemeducomharvard…

mithbseewwwphysicscisco…

yahoonasa…

nsfarpa…

navyacm…

ieeegovmilorgnetukfrThursday,May17,200737DomainNamingSystemeducomharvDNS:ArchitectureDNSserversareresponsibleforoneormoredomainsofanylevel“Rootservers”aremaintainedthroughouttheworld(oneisinPaloAlto)andareresponsibleforallofthetop-leveldomainsWhenyouregisteradomain,anentryforthatdomainisaddedtotheappropriaterootserverOwnersofeachregulardomainorsubdomainmaintain(oroutsource)theirownDNSserverscontainingthecorrectinformationThursday,May17,200738DNS:ArchitectureDNSserversaNameServersPartitionhierarchyintozoneseducomprinceton…

mitcseeux01ux04physicscisco…

yahoonasa…

nsfarpa…

navyacm…

ieeegovmilorgnetukfrRootnameserverPrincetonnameserverCisconameserverCSnameserverEEnameserver……EachzoneimplementstwoormorenameserversPrimarysecondaryThursday,May17,200739NameServersPartitionhierarchHierarchicalAdministration-“Zones”arpacomingovmilnetorgusarpaaciimcalwwwThursday,May17,200740HierarchicalAdministration-Administration-ZonesAzoneisasubtreeoftheDNStreethatisindependentlymanagedSecond-leveldomains(“ac.in”)areusuallyanindependentzoneMostsub-domains(“iimcal.ac.in”)arealsoindependent.

Azonemustprovidemultiplenameservers.Thisserverrecordsthemembersinthedomain.Youtypicallyneedaprimarynameserverandoneormoresecondarynameservers.Secondaryretrievesinformationfromprimaryusingazonetransfer.Thursday,May17,200741Administration-ZonesAzoneiResolvinganaddressA.C.DwantstoknowaboutF.E.DACDEGBFHHost“A.C.D”asks“B.C.D”(thelocalnameserver)toresolve“F.E.D”NameserversThursday,May17,200742ResolvinganaddressA.C.DwantResolvinganaddressB.C.Ddoesn’tknowtheanswer.Itwantstoasktheprimarydomainserverforthe“E.D”domain,soitaskstheparentofthe“B.C”domain(“D”inthisexample)toresolve“E.D”.DasksH,therootserver.Hdoesn’tknowtheanswer,butit’sthetop-leveldomainandknowsthat“G.E.D”istheprimarydomainserverforthe“E.D”domainB.C.DnowknowstheprimarydomainserverfortheE.Ddomain,andcannowask“G.E.D”about“F.E.D”Thursday,May17,200743ResolvinganaddressB.C.DdoesDomainserversWhatkindofrecordscanberequestedforagivendomain?AddresstranslationCachinginformationMailserverinformationAuthoritativenameserverinformationHowisthisdatarequested?Eachrecordhasatypeandcertaindataassociatedwithit–clientsrequestrecordsofacertaintypefromaserverThursday,May17,200744DomainserversWhatkindofrecDNSOrganizationDistributedDatabaseTheorganizationthatownsadomainnameisresponsibleforrunningaDNSserverthatcanprovidethemappingbetweenhostnameswithinthedomaintoIPaddresses.So-somemachinerunbyRPIisresponsibleforeverythingwithinthedomain.Thursday,May17,200745DNSOrganizationDistributedDaDNSDBDNSDBDNSDistributedDatabaseThereisoneprimaryserverforadomain,andtypicallyanumberofsecondaryserverscontainingreplicateddatabases.DNSDBAuthoritativeDNSDBReplicasDNSserverThursday,May17,200746DNSDistributedDNSClientsADNSclientiscalledaresolver.Acalltogethostbyname()ishandledbyaresolver(typicallypartoftheclient).MostUnixworkstationshavethefile/etc/resolv.confthatcontainsthelocaldomainandtheaddressesofDNSserversforthatdomain.Thursday,May17,200747DNSClientsADNSclientiscal/etc/resolv.confdomainThursday,May17,200748/etc/resolv.confdomainnslookupnslookupisaninteractiveresolverthatallowstheusertocommunicatedirectlywithaDNSserver.nslookupisusuallyavailableonUnixworkstations.(digandhostarealsoDNSclients).Thursday,May17,200749nslookupnslookupisaninteracDNSServersServershandlerequestsfortheirdomaindirectly.ServershandlerequestsforotherdomainsbycontactingremoteDNSserver(s).Serverscacheexternalmappings.Thursday,May17,200750DNSServersServershandlerequServer-ServerCommunicationIfaserverisaskedtoprovidethemappingforahostoutsideit’sdomain(andthemappingisnotintheservercache):Theserverfindsanameserverforthetargetdomain.TheserverasksthenameservertoprovidethehostnametoIPtranslation.Tofindtherightnameserver,useDNS!Thursday,May17,200751Server-ServerCommunicationIDNSDataDNSdatabasescontainmorethanjusthostname-to-addressrecords:Nameserverrecords NSHostnamealiases CNAMEMailExchangers MXHostInformation HINFOThursday,May17,200752DNSDataDNSdatabasescontainTheRootDNSServerTherootserverneedstoknowtheaddressof1st(andmany2nd)comorgjpalbanyrpiThursday,May17,200753TheRootDNSServerTherootseServerOperationIfaserverhasnoclueaboutwheretofindtheaddressforahostname,asktherootserver.Therootserverwilltellyouwhatnameservertocontact.Arequestmaygetforwardedafewtimes.Thursday,May17,200754ServerOperationIfaserverhDNSMessageFormatThursday,May17,200755DNSMessageFormatThursday,MaDNSMessageHeaderqueryidentifierflags#ofquestions#ofRRs#ofauthorityRRs#ofadditionalRRs16bitfieldsResponse}Thursday,May17,200756DNSMessageHeaderqueryidentiMessageFlagsQR:Query=0,Response=1AA:AuthoritativeAnswerTC:responsetruncated(>512bytes)RD:recursiondesiredRA:recursionavailablercode:returncodeThursday,May17,200757MessageFlagsQR:Query=0,RespRecursionArequestcanindicatethatrecursionisdesired-thistellstheservertofindouttheanswer(possiblybycontactingotherservers).Ifrecursionisnotrequested-theresponsemaybealistofothernameserverstocontact.Thursday,May17,200758RecursionArequestcanindicatQuestionFormatName:domainname(orIPaddress)Querytype(A,NS,MX,…)Queryclass(1forIP)Thursday,May17,200759QuestionFormatName:domainnaResponseResourceRecordDomainNameResponsetypeClass(IP)Timetolive(inseconds)LengthofresourcedataResourcedataThursday,May17,200760ResponseResourceRecordDomainUDP&TCPBothUDPandTCPareused:TCPfortransfersofentiredatabasetosecondaryservers(replication).UDPforlookupsIfmorethan512bytesinresponse-requestorresubmitsrequestusingTCP.Thursday,May17,200761UDP&TCPBothUDPandTCPareLotsmoreThisisnotacompletedescription!Ifinterested-lookat:RFC1034:DNSconceptsandfacilities.RFC1035:DNSimplementationandprotocolspecification.playwithnslookup.LookatcodeforBIND(DNSservercode).Thursday,May17,200762LotsmoreThisisnotacompletNametoAddressConversionThereisalibraryoffunctionsthatactasDNSclient(resolver).youdon’tneedtowriteDNSclientcodetouseDNS!WithsomeOSsyouneedtoexplicitlylinkwiththeDNSresolverlibrary:-lnsl(nslis“NameServerLibrary”)Suns(Solaris)needthis!Thursday,May17,200763NametoAddressConversionTherDNSlibraryfunctionsgethostbynamegethostbyaddrgethostbyname2IPV6!Thursday,May17,200764DNSlibraryfunctionsgethostbygethostbynamestructhostent*gethostbyname(constchar*hostname);structhostentisdefinedinnetdb.h:#include<netdb.h>Thursday,May17,200765gethostbynamestructhostent*gstructhostentstructhostent{ char*h_name; char**h_aliases; inth_addrtype; inth_length; char**h_addr_list;};officialname(canonical)othernamesAF_INETorAF_INET6addresslength(4or16)

arrayofptrstoaddressesThursday,May17,200766structhostentstructhostent{hostentpictureh_nameh_aliasesh_addrtypeh_lengthh_addr_listOfficialNamealias1alias2nullIPaddress1IPaddress2nullThursday,May17,200767hostentpictureh_nameOfficialWhichAddress?Onsuccess,gethostbynamereturnstheaddressofahostentthathasbeencreated.hasanarrayofptrstoIPaddressesUsuallyusethefirstone:#defineh_addrh_addr_list[0]Thursday,May17,200768WhichAddress?Onsuccess,gethgethostbynameanderrorsOnerrorgethostbynamereturnnull.Gethostbynamesetstheglobalvariableh_errnotoindicatetheexacterror:HOST_NOT_FOUNDTRY_AGAINNO_RECOVERYNO_DATANO_ADDRESSAlldefinedinnetdb.hThursday,May17,200769gethostbynameanderrorsOnerrGettingattheaddress:

char**h_addr_list;h=gethostbyname("");sockaddr.sin_addr.s_addr= *(h->h_addr_list[0]);Thiswon'twork!!!!

h_addr_list[0]isachar*!Thursday,May17,200770Gettingattheaddress:

char*UsingmemcpyYoucancopythe4bytes(IPv4)directly:h=gethostbyname("");memcpy(&sockaddr.sin_addr, h->h_addr_list[0],sizeof(structin_addr));

Thursday,May17,200771UsingmemcpyYoucancopythe4NetworkByteOrderAlltheIPaddressesreturnedviathehostentareinnetworkbyteorder!Repeatafterme:"Thankyougethostbyname!"Thursday,May17,200772NetworkByteOrderAlltheIPagethostbyaddrstructhostent*gethostbyaddr(constchar*addr size_tlen, intfamily);AF_INET(couldbeAF_INET6)sizeof(structin_addr)Thursday,May17,200773gethostbyaddrstructhostent*gSomeotherfunctionsuname

:gethostnameoflocalhostgetservbyname

:getportnumberforanamedservicegetservbyaddr

:getnameforserviceassociatedwithaportnumberThursday,May17,200774Someotherfunctionsuname:geReferencesRFC1034RFC1035Thursday,May17,200775ReferencesRFC1034Thursday,MaSNMP-SimpleNetworkManagementProtocolThursday,May17,200776SNMP-SimpleNetworkManagemeThirdQuestionThursday,May17,200777ThirdQuestionThursday,May17SNMPis…AnetworkmanagementtoolDesignedtoallowdataacquisitionfromSNMPcapablenetworkequipmentAllowscontrolofSNMPcapableequipmentbythedistantcontrollerBasedoninquiry/responsearchitecturewithsimpleresponseparametersThursday,May17,200778SNMPis…AnetworkmanagementUsedformanagementoffaultconditions–preventionofandresponsetonetworkfailureDesignedtomanageperformance–copingwithdeteriorationofperformanceduetocongestion,changingtrafficconditionsSNMPis…Thursday,May17,200779UsedformanagementoffaultcSNMPMessageProtocolMessagesuseUDP,ports161(requests/responses)and162(notifications)Messagetypes:GetRequest:requestvaluesofvariablesfromdeviceGetNextRequest:requestvalueofvariablefollowingtheonesuppliedGetResponse:returnvaluesSetRequest:instructdevicetosetvaluesofvariablesTrap:fromdevice-notifymonitor/managerofvaluechangeThursday,May17,200780SNMPMessageProtocolMessagesToknowmoreonSNMP“EssentialSNMP”,DouglasRMauro&KevinJSchmidt,ShroffPublishers&Distributors,Calcutta,2001Thursday,May17,200781ToknowmoreonSNMPThursday,樹(shù)立質(zhì)量法制觀念、提高全員質(zhì)量意識(shí)。12月-2212月-22Thursday,December29,2022人生得意須盡歡，莫使金樽空對(duì)月。09:04:4509:04:4509:0412/29/20229:04:45AM安全象只弓，不拉它就松，要想保安全，常把弓弦繃。12月-2209:04:4509:04Dec-2229-Dec-22加強(qiáng)交通建設(shè)管理，確保工程建設(shè)質(zhì)量。09:04:4509:04:4509:04Thursday,December29,2022安全在于心細(xì)，事故出在麻痹。12月-2212月-2209:04:4509:04:45December29,2022踏實(shí)肯干，努力奮斗。2022年12月29日9:04上午12月-2212月-22追求至善憑技術(shù)開(kāi)拓市場(chǎng)，憑管理增創(chuàng)效益，憑服務(wù)樹(shù)立形象。29十二月20229:04:45上午09:04:4512月-22嚴(yán)格把控質(zhì)量關(guān)，讓生產(chǎn)更加有保障。十二月229:04上午12月-2209:04December29,2022作業(yè)標(biāo)準(zhǔn)記得牢，駕輕就熟除煩惱。2022/12/299:04:4509:04:4529December2022好的事情馬上就會(huì)到來(lái)，一切都是最好的安排。9:04:45上午9:04上午09:04:4512月-22一馬當(dāng)先，全員舉績(jī)，梅開(kāi)二度，業(yè)績(jī)保底。12月-2212月-2209:0409:04:4509:04:45Dec-22牢記安全之責(zé)，善謀安全之策，力務(wù)安全之實(shí)。2022/12/299:04:45Thursday,December29,2022相信相信得力量。12月-222022/12/299:04:4512月-22謝謝大家！樹(shù)立質(zhì)量法制觀念、提高全員質(zhì)量意識(shí)。12月-2212月-22DHCP,DNS,SNMPDebashisSahaMISGroup,IIMCalcuttads@iimcal.ac.in83DHCP,DNS,SNMP1FirstQuestionThursday,May17,200784FirstQuestionThursday,May17TheInternetandAddressingAllmachinesontheInternetareaccessedviatheirIPaddressDottedquad:xxx.xxx.xxx.xxxProblem:IPaddressesarehardtorememberandhardtostaticallyassignonlargenetworksSolution:NeedtocomeupwithawaytoautomaticallyassignIPaddressesandatextbasedrepresentationofmachineaddressesinsteadofjust4numbersThursday,May17,200785TheInternetandAddressingAllAddressingSolutionsTwoprotocolshavebeendevelopedtosolvetheseproblemsDHCP–automaticnetworkconfiguration(includingIPaddress)DNS–translatestextualbasednamesintoIPaddressesandviceversaThursday,May17,200786AddressingSolutionsTwoprotocDHCP–DynamicHostConfigurationProtocolThursday,May17,200787DHCP–DynamicHostConfiguratDHCPAllowsclientmachinestoreceiveanIPaddress,DNSinformation,etcautomaticallyBeforeDHCPcameintouse,usershadtotypeinallthisinformationbyhand,whichisbad:EasytomistypesomethingwhenenteringbyhandManuallychangingnetworkconfigurationeverytimeyoumoveyourlaptopisapainBootpresolvedsomeoftheseissues…andDHCPstillusesthesameportasbootpThursday,May17,200788DHCPAllowsclientmachinestoPurposeofDHCP FromRFC-2131(theInternetstandard):TheDynamicHostConfigurationProtocol(DHCP)providesaframeworkforpassingconfigurationinformationtohostsonaTCP/IPnetwork.DHCPconsistsoftwocomponents:aprotocolfordeliveringhost-specificconfigurationparametersfromaDHCPservertoahostandamechanismforallocationofnetworkaddressestohosts.Thursday,May17,200789PurposeofDHCP FromRFC-2131DHCPfunctionalgoalsAhostwithoutavalidIPaddresslocatesandcommunicateswithaDHCPserverADHCPserverpassesconfigurationparameters,includinganIPaddress,tothehostTheDHCPservermaydynamicallyallocateaddressestohostsandreuseaddressesHostscandetectwhentheyrequireanewIPaddressUnavailabilityofDHCPserverhasminimaleffectonoperationofhostsThursday,May17,200790DHCPfunctionalgoalsAhostwiDHCP:BasicsAclientleasesanIPaddressfromaDHCPserverforagivenamountoftimeWhenleaseexpires,theclientmustaskDHCPserverforanewaddress(clientsattempttorenewleaseafter50%oftheleasetimehasexpired)Typicalleasesmaylastforfrom30secondsto24hours,orevenlonger.Thursday,May17,200791DHCP:BasicsAclientleasesanWhatdoesDHCPdo?Providesprotocolstack,applicationandotherconfigurationparameterstohostsEliminatesneedforindividual,manualconfigurationforhostsIncludesadministrativecontrolsfornetworkadministratorsBackwardcompatiblepacketformatforBOOTPinteroperation(RFC1542)Cancoexistwithhoststhathavepre-assignedIPaddressesandhoststhatdonotparticipateinDHCPThursday,May17,200792WhatdoesDHCPdo?ProvidesproDesignGoalsEliminatemanualconfigurationofhostsPreventuseofanyIPaddressbymorethanonehostShouldnotrequireaserveroneverysubnetAllowformultipleDHCPserversProvideamechanism,notapolicyProvidethesameconfiguration-includingIPaddress-toahostwheneverpossibleThursday,May17,200793DesignGoalsEliminatemanualcWhatcanyoudowithDHCPPlug-and-playMovedesktopPCsbetweenofficesRenumberOtherrestructuring-changesubnetmasksMobileIP-laptopsMovingequipment-cartableThursday,May17,200794WhatcanyoudowithDHCPPlug-WhatDHCPdoesn’tdoSupportmultipleaddressesperinterfaceInformrunninghostthatparametershavechangedPropagatenewaddressestoDNSSupportinter-servercommunicationProvideauthenticatedmessagedeliveryConfigureroutersandothernetworkequipmentDesignnetworkaddressingplanDetermineotherconfigurationparametersLocateotherserversThursday,May17,200795WhatDHCPdoesn’tdoSupportmuDHCP:MessagesOverviewSeveralmessagesaresentbackandforthbetweenaclientandtheDHCPserverbeforeitcansuccessfullyobtainanIPaddressThursday,May17,200796DHCP:MessagesOverviewSeveralDHCP:DISCOVERHardcodingtheaddressesofDHCPserverskindofdefeatsthepurposeofautomaticconfigurationSolution:AclientusingDHCPwillbroadcastaDISCOVERmessagetoallcomputersonitssubnet(addr55)tofigureouttheIPaddressofanyDHCPserversMostroutersareconfiguredtopassthisrequestwithinthecampusorenterpriseThursday,May17,200797DHCP:DISCOVERHardcodingtheaDHCP:OFFER(Optionally)sentfromserverinresponsetoaDISCOVERContainsanIPaddress,otherconfigurationinformationaswell(subnetmask,DNSservers,defaultgateway,searchdomains,etc)NotethatallDHCPserversthatreceiveaDISCOVERrequestmaysendanOFFER;sinceaclienttypicallydoesnotneedmorethanoneIPaddress,moremessagesneededtozeroononeIPThursday,May17,200798DHCP:OFFER(Optionally)sentfDHCP:REQUESTSentbyclienttorequestacertainIPaddressUsuallytheonesentbyanOFFER,butalsousedtorenewleases.Alsocanbesenttotrytogetsameaddre