基于IOS配置DHCP

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1、CiscoIOSDHCPServerFeatureOverviewDynamicHostControlProtocol(DHCP)enablesyoutoautomaticallyassignreusableIPaddressestoDHCPclients.TheCiscoIOSDHCPServerfeatureisafullDHCPserverimplementationthatassignsandmanagesIPaddressesfromspecifiedaddresspoolswithintheroutertoDHCPcl

2、ients.IftheCiscoIOSDHCPServercannotsatisfyaDHCPrequestfromitsowndatabase,itcanforwardtherequesttooneormoresecondaryDHCPserversdefinedbythenetworkadministrator.Figure1showsthebasicstepsthatoccurwhenaDHCPclientrequestsanIPaddressfromaDHCPserver.Theclient,HostA,sendsaDHC

3、PDISCOVERbroadcastmessagetolocateaCiscoIOSDHCPServer.ADHCPserveroffersconfigurationparameters(suchasanIPaddress,aMACaddress,adomainname,andaleasefortheIPaddress)totheclientinaDHSCPOFFERunicastmessage.Figure1DHCPRequestforanIPAddressfromaDHCPServerDHCPDISCOVER(broadcas

4、t)HostACiscoIOSDHCPOFFER(unicast)DHCPserverDHCPREQUEST(broadcast)DHCPACK(unicast)32369NoteADHCPclientmayreceiveoffersfrommultipleDHCPserversandcanacceptanyoneoftheoffers;however,theclientusuallyacceptsthefirstofferitreceives.Additionally,theofferfromtheDHCPserverisnot

5、aguaranteethattheIPaddresswillbeallocatedtotheclient;however,theserverusuallyreservestheaddressuntiltheclienthashadachancetoformallyrequesttheaddress.TheclientreturnsaformalrequestfortheofferedIPaddresstotheDHCPserverinaDHCPREQUESTbroadcastmessage.TheDHCPserverconfirm

6、sthattheIPaddresshasbeenallocatedtotheclientbyreturningaDHCPACKunicastmessagetotheclient.CiscoIOSDHCPServer1BenefitsNoteTheformalrequestfortheofferedIPaddress(theDHCPREQUESTmessage)thatissentbytheclientisbroadcastsothatallotherDHCPserversthatreceivedtheDHCPDISCOVERbr

7、oadcastmessagefromtheclientcanreclaimtheIPaddressesthattheyofferedtotheclient.IftheconfigurationparameterssenttotheclientintheDHCPOFFERunicastmessagebytheDHCPserverareinvalid(amisconfigurationerrorexists),theclientreturnsaDHCPDECLINEbroadcastmessagetotheDHCPserver.TheD

8、HCPserverwillsendtotheclientaDHCPNAKdenialbroadcastmessage,whichmeanstheofferedconfigurationparametershavenotbeenassigned,ifanerrorh