管理才能考核表Title

LectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20071DHCP,DNS,SNMPDebashisSahaMISGroup,[e-mail],DNS&SNMPDebashisSahaThursday,May17,20072FirstQuestion•HowdoesyourcomputerknowwhichIPtouse?•Howdoesyourcomputerknowthat•Howcanyoutrackyournetwork’shealth?LectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20073TheInternetandAddressing•AllmachinesontheInternetareaccessedviatheirIPaddress–Dottedquad:xxx.xxx.xxx.xxx•Problem:IPaddressesarehardtorememberandhardtostaticallyassignonlargenetworks•Solution:NeedtocomeupwithawaytoautomaticallyassignIPaddressesandatextbasedrepresentationofmachineaddressesinsteadofjust4numbersLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20074AddressingSolutions•Twoprotocolshavebeendevelopedtosolvetheseproblems–DHCP–automaticnetworkconfiguration(includingIPaddress)–DNS–translatestextualbasednamesintoIPaddressesandviceversaLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20075DHCP–DynamicHostConfigurationProtocolLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20076DHCP•AllowsclientmachinestoreceiveanIPaddress,DNSinformation,etcautomatically•BeforeDHCPcameintouse,usershadtotypeinallthisinformationbyhand,whichisbad:–Easytomistypesomethingwhenenteringbyhand–Manuallychangingnetworkconfigurationeverytimeyoumoveyourlaptopisapain–Bootpresolvedsomeoftheseissues•…andDHCPstillusesthesameportasbootpLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20077PurposeofDHCPFromRFC-2131(theInternetstandard):•TheDynamicHostConfigurationProtocol(DHCP)providesaframeworkforpassingconfigurationinformationtohostsonaTCP/IPnetwork.•DHCPconsistsoftwocomponents:–aprotocolfordeliveringhost-specificconfigurationparametersfromaDHCPservertoahostand–amechanismforallocationofnetworkaddressestohosts.LectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20078DHCPfunctionalgoals•AhostwithoutavalidIPaddresslocatesandcommunicateswithaDHCPserver•ADHCPserverpassesconfigurationparameters,includinganIPaddress,tothehost•TheDHCPservermaydynamicallyallocateaddressestohostsandreuseaddresses•HostscandetectwhentheyrequireanewIPaddress•UnavailabilityofDHCPserverhasminimaleffectonoperationofhostsLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,20079DHCP:Basics•AclientleasesanIPaddressfromaDHCPserverforagivenamountoftime•Whenleaseexpires,theclientmustaskDHCPserverforanewaddress(clientsattempttorenewleaseafter50%oftheleasetimehasexpired)•Typicalleasesmaylastforfrom30secondsto24hours,orevenlonger.LectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200710WhatdoesDHCPdo?•Providesprotocolstack,applicationandotherconfigurationparameterstohosts•Eliminatesneedforindividual,manualconfigurationforhosts•Includesadministrativecontrolsfornetworkadministrators•BackwardcompatiblepacketformatforBOOTPinteroperation(RFC1542)•Cancoexistwithhoststhathavepre-assignedIPaddressesandhoststhatdonotparticipateinDHCPLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200711DesignGoals•Eliminatemanualconfigurationofhosts•PreventuseofanyIPaddressbymorethanonehost•Shouldnotrequireaserveroneverysubnet•AllowformultipleDHCPservers•Provideamechanism,notapolicy•Providethesameconfiguration-includingIPaddress-toahostwheneverpossibleLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200712WhatcanyoudowithDHCP•Plug-and-play•MovedesktopPCsbetweenoffices•Renumber•Otherrestructuring-changesubnetmasks•MobileIP-laptops•Movingequipment-cartableLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200713WhatDHCPdoesn’tdo•Supportmultipleaddressesperinterface•Informrunninghostthatparametershavechanged•PropagatenewaddressestoDNS•Supportinter-servercommunication•Provideauthenticatedmessagedelivery•Configureroutersandothernetworkequipment•Designnetworkaddressingplan•Determineotherconfigurationparameters•LocateotherserversLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200714DHCP:MessagesOverview•SeveralmessagesaresentbackandforthbetweenaclientandtheDHCPserverbeforeitcansuccessfullyobtainanIPaddressLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200715DHCP:DISCOVER•HardcodingtheaddressesofDHCPserverskindofdefeatsthepurposeofautomaticconfiguration•Solution:AclientusingDHCPwillbroadcastaDISCOVERmessagetoallcomputersonitssubnet(addr255.255.255.255)tofigureouttheIPaddressofanyDHCPservers•MostroutersareconfiguredtopassthisrequestwithinthecampusorenterpriseLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200716DHCP:OFFER•(Optionally)sentfromserverinresponsetoaDISCOVER•ContainsanIPaddress,otherconfigurationinformationaswell(subnetmask,DNSservers,defaultgateway,searchdomains,etc)•NotethatallDHCPserversthatreceiveaDISCOVERrequestmaysendanOFFER;–sinceaclienttypicallydoesnotneedmorethanoneIPaddress,moremessagesneededtozeroononeIPLectureonDHCP,DNS&SNMPDebashisSahaThursday,May17,200717DHCP:REQUEST•SentbyclienttorequestacertainIPaddress–UsuallytheonesentbyanOFFER,butalsousedtorenewleases.Alsocanbesenttotrytogetsameaddressafterareboot•Thismessageisbroadcast•MostOSsbydefaultwillsendaREQUESTforthefirstOFFERtheyreceive–thismeansthatifthereisarogueDHCPserveronyoursu