How To Plan Out Your Own Version Of Hpl (Dhcp) On A Network With A Network (Dns) On Your Network (Dhpl) On An Ipad Or Ipad On A Pc Or Ipa On A Server On A

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System

i

Networking

Dynamic

Host

Configuration

Protocol

Version

5 Release

4

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System

i

Networking

Dynamic

Host

Configuration

Protocol

Version

5 Release

4

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Note

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Dynamic

Host

Configuration

Protocol

.

. 1

PrintablePDF . . . 1

DHCPconcepts . . . 1

DHCPclient/serverinteraction . . . 1

Leases . . . 3

Relayagentsandrouters . . . 5

DHCPclientsupport . . . 6

BOOTP . . . 7

Dynamicupdates. . . 7

DHCPoptionslookup . . . 8

Examples:DHCP . . . 22

Example:SimpleDHCPsubnet. . . 23

Example:MultipleTCP/IPsubnets . . . 25

Example:DHCPandmultihoming. . . 27

Example:DNSandDHCPonthesameSystemi 31 Example:DNSandDHCPondifferentSystemi models . . . 33

Example:PPPandDHCPonasingleSystemi. . 35

Example:DHCPandPPPprofileondifferent Systemimodels. . . 37

PlanningforDHCP. . . 40

Securityconsiderations . . . 40

Networktopologyconsiderations . . . 40

ConfiguringDHCP. . . 43

ConfiguringtheDHCPserverand BOOTP/DHCPrelayagent . . . 43

ConfiguringorviewingtheDHCPserver . . 44

StartingorstoppingtheDHCPserver . . . 44

ConfiguringtheDHCPservertobestarted automatically. . . 44

AccessingtheDHCPservermonitor . . . . 44

ConfiguringtheBOOTP/DHCPrelayagent 45 StartingorstoppingtheBOOTP/DHCPrelay agent . . . 45

ConfiguringtheBOOTP/DHCPrelayagentto bestartedautomatically . . . 45

ConfiguringclientstouseDHCP . . . 45

EnablingDHCPforWindowsMeclients . . 45

CheckingtheDHCPleaseforWindowsMe clients . . . 45

EnablingDHCPforWindows2000clients . . 46

CheckingtheMACaddressandDHCP lease. . . 46

UpdatingDNSArecords . . . 46

EnablingDHCPforWindowsXPclients. . . 47

CheckingtheMACaddressandDHCP lease. . . 47

UpdatingDNSArecords . . . 47

ConfiguringDHCPtosenddynamicupdatesto DNS. . . 47

DisablingDNSdynamicupdates . . . 48

ManagingleasedIPaddresses . . . 49

TroubleshootingDHCP . . . 49

GatheringdetailedDHCPerrorinformation . . 49

TracingtheDHCPserver . . . 49

Problem:ClientsarenotreceivinganIPaddress ortheirconfigurationinformation . . . 50

Problem:DuplicateIPaddressassignmentson thesamenetwork . . . 51

Problem:DNSrecordsarenotbeingupdatedby DHCP . . . 51

Problem:DHCPjobloghasDNS030Bmessages witherrorcode3447 . . . 52

RelatedinformationforDHCP . . . 53

Appendix.

Notices

.

. 55

ProgrammingInterfaceInformation . . . 56

Trademarks . . . 57

Termsandconditions . . . 57

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Dynamic

Host

Configuration

Protocol

DynamicHostConfigurationProtocol(DHCP)isaTCP/IPstandardthatusesacentralservertomanage IPaddressesand otherconfigurationdetailsforanentirenetwork.

ADHCPserverrespondstorequestsfromclients, dynamicallyassigningpropertiestothem.

Printable

PDF

Usethistoview andprintaPDFofthis information.

ToviewordownloadthePDFversionofthisdocument,selectDHCP(about1399KB).

Saving

PDF

files

Tosavea PDFonyour workstationforviewingorprinting:

1. Right-clickthePDFinyourbrowser(right-click thelinkabove).

2. Click theoption thatsavesthePDFlocally.

3. Navigatetothedirectoryinwhichyouwanttosave thePDF.

4. Click Save.

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DHCP

concepts

DynamicHostConfigurationProtocol(DHCP)provides anautomatedmethodfordynamicclient configuration.Here aresomeDHCP-relatedconceptstohelpyoubetterunderstandDHCP.

DHCP

client/server

interaction

TheinteractionbetweenDynamicHostConfigurationProtocol(DHCP)clients andserversenablesa clienttoobtainitsIPaddressand correspondingconfigurationinformationfromaDHCPserver. Thisprocess occursthrough aseries ofsteps,illustratedinthefollowingfigure.

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mightalsocontainotherrequests,suchasrequestedoptions(forexample,subnetmask,domain nameserver,domainname,orstaticroute).Themessageissentoutasa broadcast.Ifthe networkcontains routers,those routerscanbeconfiguredtoforwardDISCOVERpacketsto DHCPserversonattached networks.

DHCPserveroffersinformationtoclient:DHCPOFFER

AnyDHCPserverthatreceivestheDISCOVERmessagemight sendanOFFERmessagein response.TheDHCPservermight notsendanOFFERmessagebacktotheclientformultiple reasons:themostcommonreasonsarethatallavailableaddressesarecurrentlyleased,thesubnet isnotconfigured,ortheclientisnotsupported. IftheDHCPserversendsan OFFERmessagein response,theDHCPOFFERwillcontainan availableIPaddressandanyotherconfiguration informationthatisdefinedintheDHCPsetup.

ClientacceptsDHCPserveroffer:DHCPREQUEST

TheclientreceivesOFFERmessages fromtheDHCPserversthatresponded totheDISCOVER messages.Theclientcomparestheoffers withthesettingsthatitrequested,andthenselectsthe serverthatitwantstouse.ItsendsaREQUESTmessagetoaccepttheoffer,indicatingwhich serveritselected.Thismessageisbroadcasttotheentirenetworktolet allDHCPserversknow whichserverwas selected.

DHCPserveracknowledgestheclientandleasestheIPaddress:DHCPACK

IfaserverreceivesaREQUESTmessage,theservermarkstheaddressasleased.Serversthatare notselectedwillreturnofferedaddressestotheiravailablepool. Theselectedserversendsthe clientanacknowledgment(DHCPACK),whichcontainsadditionalconfigurationinformation. Theclientmightnow usetheIPaddressandconfigurationparameters.Itwillusethesesettings untilitsleaseexpiresoruntil theclientsendsa DHCPRELEASEmessagetotheservertoendthe lease.

Clientattemptstorenew thelease:DHCPREQUEST,DHCPACK

Theclientstartstorenewaleasewhenhalfoftheleasetimehaspassed.Theclientrequeststhe renewalbysendingaREQUESTmessagetotheserver.Iftheserveracceptstherequest,it will sendaDHCPACK messagebacktotheclient.Iftheserverdoesnotrespondtotherequest, the clientmightcontinuetousetheIPaddressand configurationinformationuntil theleaseexpires. Aslongastheleaseisstillactive,theclientandserverdonotneedtogo throughthe

DHCPDISCOVERandDHCPREQUEST process.Whentheleasehasexpired,theclientmuststart overwith theDHCPDISCOVER process.

Clientends thelease:DHCPRELEASE

TheclientendstheleasebysendingaRELEASEmessagetotheDHCPserver.Theserverwill thenreturntheclient’sIPaddresstotheavailableaddresspool.

Related concepts

“Relayagentsandrouters”onpage5

Dynamic HostConfigurationProtocol(DHCP)relayagentsandrouterscanbeusedtoefficientlyand securelytransferdatathroughoutthenetwork.

“Leases”

WhenDHCPsendsconfigurationinformationtoaclient,theinformationissentwith aleasetime. ThisisthelengthoftimethattheclientcanusetheIPaddressithasbeenassigned.Thedurationof theleasetimecanbechangedaccording toyourspecific requirement.

Leases

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tomakeconfigurationchangestoalloftheclients onthenetworkinalimited amountoftime. Whenthe leaseexpires,theclientwillrequesta newleasefromDHCP.Iftheconfigurationdatahaschanged,the newdatawillbesenttotheclientatthattime.

Lease

renewal

Theclientstartstorenewaleasewhenhalfoftheleasetimehaspassed.For example,for a24-hourlease, theclientwillattempttorenewtheleaseafter 12hours.Theclient requeststherenewalbysendinga DHCPREQUESTmessagetotheserver.Therenewalrequestcontains thecurrentIPaddressand configurationinformationof theclient.

Iftheserveracceptstherequest, itwillsend anDHCPACKmessagebacktotheclient.Iftheserverdoes notrespondtotherequest, theclientcancontinuetousetheIPaddress andconfigurationinformation untiltheleaseexpires.If theleaseisstill active,theclientand serverdonotneedtogothrough the DHCPDISCOVERand DHCPREQUESTprocess.Whentheleasehasexpired,theclientmust startover withtheDHCPDISCOVERprocess.

Iftheserverisunreachable, theclientcancontinuetousetheassignedaddressuntil theleaseexpires.In thepreviousexample,theclienthas12hoursfromwhenitfirst triestorenew theleaseuntilthelease expires.Duringa12-houroutage,newuserscannotgetnewleases,butnoleaseswillexpireforany computerturnedonat thetimethattheoutagestarts.

Determining

lease

duration

ThedefaultleasetimefortheDHCPserveris24hours.Thedurationforwhichyousettheleasetimeon yourDHCPserverdependsonseveralfactors.Youneedtoconsideryour goals,your site’susage

patterns,andservicearrangements foryourDHCPserver.Thefollowingquestionscanhelpyouto decideonanappropriate leasetime.

Doyouhave moreusersthanaddresses?

Ifso,theleasetimeshouldbeshortsothatclients donotneedtowaitforunused leasesto expire.

Doyouhave aminimumamount oftimethatyouneedto support?

Ifyourtypicaluser isonforanhouratminimum,thatsuggestsanhourleaseat minimum.

HowmuchDHCPmessagetraffic canyournetworkhandle?

Ifyouhavealargenumber ofclientsorslow communicationlinesoverwhichtheDHCPpackets willrun,networktrafficmight causeproblems.Theshorterthelease,theheaviertraffictheserver andnetworkloadfromtherenewalrequestonyournetwork.

Whatkind ofserviceplandoyouhave inplace,andtowhatextentcanyournetworkhandlean outage?

Consideranyroutinemaintenance,andthepotentialimpactof anoutage.If theleasetimeisat leasttwicetheserveroutagetime,then runningclientswhoalreadyhaveleaseswillnotlose them.Ifyouhaveagoodideaofyour longestlikelyserveroutage,youcanavoidsuchproblems.

Whattypeofnetwork environmentistheDHCPserverin?Whatdoesa typicalclient do?

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thenetworkduringbusinesshours.Inthiscase,if youspecifyashorterleasetime,theDHCP servernegotiatestheleaserenewalmuchmorefrequentlywiththeclients,whichcausesexcess networktraffic.

Howmuchdoesyournetwork configurationchange?

Ifyournetworktopologychangesquitefrequently,youmight wanttostay awayfromlonger leases.Long leasescanbe disadvantageousincaseswhereyouneedtochangea configuration parameter.The lengthoftheleasecanmeanthedifferencebetweenhavingtogotoeveryaffected clientandrestartingit,ormerelywaitinga certainamountoftimefortheleasestoberenewed. Ifyournetworktopologyrarelychangesand youhaveenoughIPaddressesinyouraddresspool, youcanconfigureDHCPtouseinfiniteleases--leasesthatneverexpire.However, infiniteleases arenotrecommended.Ifyouuseaninfinitelease,theIPaddress isleasedtotheclient

indefinitely.Theseclientsdo notneedtogo throughanyleaserenewalprocess aftertheyreceive theinfinitelease.Afteraninfiniteleaseisassignedtoaclient,thataddresscannotbeassignedto anotherclient.Therefore,therecanbe problemswithinfiniteleasesifyouwanttoassignthat clientanew IPaddress orleasetheclient’sIPaddress toanotherclientlater.

Youmight haveclientsinyour network,suchasafileserver,thatwillalwaysreceivethesameIP address.Ratherthanusinganinfinitelease,youshouldassignaspecific addressfortheclient andgiveita longleasetime.Theclientstill hastoleaseitfora givenamountoftimeandrenew thelease, buttheserverwillreservetheIPaddress forthatclientonly.Then,ifyougeta newfile server,forexample,youcanjustchangetheclientidentifier(MACaddress) andtheserverwill givethenewfileserverthatsameaddress.Ifyouhavegivenitan infinitelease,then theDHCP servercannotgiveout theaddress againunlesstheleaseisexplicitlydeleted.

“Networktopologyconsiderations”onpage40

Youneedtotakeintoconsiderationseveralfactorswhen planningforyour DynamicHost

ConfigurationProtocol(DHCP)setup,suchasyour networktopology, thedevicesonthenetwork(for example,routers),andhow youwanttosupportyourclients inDHCP.

Related reference

“DHCPclient/serverinteraction”onpage1

Theinteraction betweenDynamic HostConfigurationProtocol(DHCP)clientsand serversenablesa clienttoobtainitsIPaddressandcorrespondingconfigurationinformationfroma DHCPserver.

Relay

agents

and

routers

DynamicHostConfigurationProtocol(DHCP)relayagentsandrouters canbe usedtoefficientlyand securelytransfer datathroughoutthenetwork.

Initially,DHCPclients broadcasttheirDISCOVERpacketsbecausetheydo notknowwhatnetworkthey areconnectedto.Insomenetworks,theDHCPservermight notbeonthesameLANastheclient. Therefore,it isnecessarytoforwardtheclient’sbroadcastDHCPpacketstotheLANwheretheDHCP serveris.Some routersareconfiguredtoforwardDHCPpackages.IfyourroutersupportsDHCPpacket forwarding,thatisall youneed.However,manyroutersdo notforwardpacketsthathaveadestination IPaddressofthebroadcastaddress(DHCPpackets).Inthiscase,if theroutercannotforwardDHCP packets,then theLANmusthaveaBootstrapprotocol(BOOTP)/DHCPrelayagenttoforwardtheDHCP packetstotheLAN thathastheDHCPserver.Referto“Example:DHCPandPPPprofileondifferent Systemimodels”onpage37forasamplenetworkusingarelayagentanda router.

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Youneedtotakeintoconsiderationseveralfactors whenplanningforyour DynamicHost

Related tasks

“ConfiguringtheDHCPserverand BOOTP/DHCPrelayagent”onpage43

ThistopicexplainswhatsoftwareyouneedtousetoconfigureaSystemi™_DHCP_server._It_also

includesinstructionstoworkwith theDHCPconfiguration,tousetheDHCPservermonitor,andto set upaDHCP/BOOTPrelayagent.

“DHCPclient/serverinteraction”onpage1

Theinteraction betweenDynamic HostConfigurationProtocol(DHCP)clientsand serversenablesa clienttoobtainitsIPaddressandcorrespondingconfigurationinformationfroma DHCPserver.

DHCP

client

support

ADHCPserverenablesyoutomanageeachclientin yournetworkindividually,ratherthanmanagingall oftheclientsasalargegroup (subnet).

ThisDHCPsetupmethodallows onlytheclientsidentified bytheDHCPservertoreceiveIPaddressand configurationinformation.

PeopleoftenthinkaboutusingDHCPtodistributeIPaddressesfroman addresspooltoasubnetof clients.AnyclientthatrequestsDHCPinformationfromthenetworkmightreceiveanIPaddressfrom theaddresspoolwhen youusesubnets,unlesstheyareexplicitlyexcluded bytheDHCPadministrator. However,theDHCPserverisalsocapable oftheinverse--limitingDHCPservicetoonlyspecific clients. TheDHCPservercanlimitserviceat theindividual clientlevelorbythetypeofclient(Bootstrap protocol(BOOTP)orDHCP).

Tolimitserviceattheindividualclient level,youmust identifyeachnetworkclientindividuallyinyour DHCPconfiguration. Eachclientisidentified byitsclientID(typicallytheirMAC address).Onlythe clientsthatareidentified intheDHCPconfigurationwillbe servedanIPaddressandconfiguration informationfromtheDHCPserver.Ifa clientisnotlisted intheDHCPconfiguration,it isrefused service bytheDHCPserver.Thismethodpreventsunknownhosts fromobtaininganIPaddressand

configurationinformationfromtheDHCPserver.

Ifyouwantevenmore controloveryournetworkclientsand theconfigurationinformationthatthey receive,youcanset upyourDHCPclientstoreceiveastaticIPaddressratherthanreceivingan IP addressfromanaddress pool.Ifyouset uptheclienttoreceivea definedIPaddress,thatclientshould betheonlyclientthatcanreceivethatIPaddresstoavoidaddressoverlap.IfyouusedynamicIP addressallocation,theDHCPserverwillmanageIPaddressassignmentfortheclients.

Ona broaderlevel,theDHCPservercanlimitservicetoaclientbased onthetype ofclient(BOOTPor DHCP).TheDHCPservercanrefuse servicetoBOOTPclients.

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BOOTP

TheBootstrapProtocol(BOOTP)isa hostconfigurationprotocolthatwasusedbeforetheDynamicHost ConfigurationProtocol (DHCP)wasdeveloped.BOOTPsupportisasubsetofDHCP.

InBOOTP,clients areidentifiedbytheirMACaddressesandare assigneda specificIPaddress. Essentially,eachclientinyour networkismappedtoanIPaddress.Thereisnodynamicaddress

assignment,eachnetworkclientmustbe identifiedintheBOOTPconfiguration, andtheclientscanonly receivea limitedamount ofconfigurationinformationfromtheBOOTPserver.

BecauseDHCPisbasedonBOOTP,theDHCPservercansupportBOOTPclients.Ifyouare currently usingBOOTP,youcansetupanduseDHCPwithoutanyimpactstoyourBOOTPclients.Tosupport BOOTPclients successfully,youmustspecifytheIPaddressofthebootstrapserverandthebootfile nameoption (option67),andBOOTPsupport mustbe turnedonfortheentiresystemorvarioussubnets. UsingDHCPtosupportBOOTPclients ispreferredoverusingaBOOTPserver.Evenwhenyouuse DHCPtosupport yourBOOTPclients,eachBOOTPclientisessentially beingmappedtoa singleIP address,andthataddressisthereforenotreusable byanotherclient.Theadvantage,however,ofusing DHCPinthiscaseisthatthereisnoneedtoconfigurea one-to-onemappingofBOOTPclients toIP addresses.TheDHCPserverwillstilldynamically assignan IPaddressestotheBOOTPclientfromthe addresspool.AftertheIPaddressisassignedtotheBOOTPclient,itispermanentlyreservedforuseby thatclientuntilyouexplicitlydeletetheaddress reservation.Eventually,youmight wanttoconsider convertingyourBOOTPclients toDHCPforeasierhost configurationmanagement.

“DHCPclientsupport”onpage6

ADHCPserverenablesyoutomanage eachclientinyournetworkindividually,ratherthan managingalloftheclientsasa largegroup(subnet).

BOOTP

Dynamic

updates

ADynamicHostConfigurationProtocol(DHCP)servercanbeconfiguredtoworkwith aDomainName System(DNS)servertodynamically updatetheclientinformationintheDNSwhenDHCPassignsthe clientanIPaddress.

DNSisa distributeddatabase systemformanaginghostnamesand theirassociatedIPaddresses.DNS enablesuserstolocatehostsusingsimplenames,suchaswww.example.com,ratherthanbyusingtheIP address(xxx.xxx.xxx.xxx).

Inthepast, allDNSdatawasstoredinstaticdatabases.AllDNSresourcerecordshad tobecreatedand maintainedbytheadministrator.Now,DNSservers runningBIND8 canbeconfiguredtoacceptrequests fromothersourcestoupdatezonedatadynamically.

Youcanconfigureyour DHCPservertosend updaterequeststotheDNSservereachtimeit assignsa newaddresstoa host.Thisautomated processreducesDNSserveradministrationinrapidlygrowingor changingTCP/IPnetworks,and innetworkswherehostschangelocations frequently.Whenaclient |

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sendanupdatetotheDNSserversootherhostsinthenetworkcanlocatetheclientthrough DNS queriesatitsnewIPaddress.For eachrecordthatisupdateddynamically, anassociatedtext(TXT) recordwillbewritten toidentifythattherecord waswrittenbyDHCP.

Note: IfyousetDHCPtoupdateonlyPTRrecords,youmustconfigure DNStoallowupdatesfrom

clients sothateachclientcanupdateitsArecord.

Dynamiczonesaresecuredbycreatinga listofauthorizedsourcesthatare allowedtosendupdates. DNSverifiesthatincoming requestpacketsare comingfromanauthorizedsourcebefore updatingthe resourcerecords.

DynamicupdatescanbeperformedbetweenDNSandDHCPona singleSystemimodel,different Systemimodels,orothersystemsthatare capableofdynamicupdates.

Related concepts DomainNameSystem

Youneedtotakeintoconsiderationseveralfactors whenplanningforyour DynamicHost

“Problem:DNSrecordsarenotbeingupdatedbyDHCP”onpage51

TheSystemiDHCPserveriscapable ofdynamicallyupdatingDNSresourcerecords.Dynamic updateerrorsmight becausedbythefailureofupdatingDNSrecordsupdate.

Related tasks

“ConfiguringDHCPtosenddynamicupdatestoDNS”onpage47

TheDynamic HostConfigurationProtocol(DHCP)servercanbeconfiguredtosend updaterequests totheDNSservereachtimeit assignsanewaddress toahost.ThisautomatedprocessreducesDNS serveradministrationinrapidlygrowingorchangingTCP/IPnetworks,andinnetworkswherehosts changelocationsfrequently.

Configuring DNStoreceivedynamicupdates Related reference

DomainNameSystemresourcerecords

DHCP

options

lookup

DynamicHostConfigurationProtocol(DHCP)hasmanyconfigurationoptionsthatcanbesenttothe clientswhentheyrequestinformationfromtheDHCPserver.Youcanusealookuptooltoseeallof the DHCPoptions.

DHCPoptionsdefineadditionalconfigurationdatathattheDHCPserverpassesalongtoclientsin additiontoanIPaddress.Typicaloptionsincludesubnetmask, domainname,routerIPaddresses, domainnameserverIPaddresses,andstaticroutes.

StandardDHCPoptions,basedondefinitionsinRFC2132:DHCPOptions andBOOTPVendor

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Table1.StandardDHCPoptions Option

number Option Description

1 Subnetmask Thesubnetmaskoptionspecifiestheclient’ssubnetmaskasperRequestfor Comments(RFC)950.Ifboththesubnetmaskandtherouteroptionare specifiedinaDHCPreply,thesubnetmaskoptionmustbespecifiedfirst. Thecodeforthesubnetmaskoptionis1,anditslengthis4octets.

2 Timeoffset Thetimeoffsetfieldspecifiestheoffsetoftheclient’ssubnetinsecondsfrom CoordinatedUniversalTime(UTC).Theoffsetisexpressedasatwo’s

complement32-bitinteger.Apositiveoffsetindicatesalocationeastofthezero meridianandanegativeoffsetindicatesalocationwestofthezeromeridian. Thecodeforthetimeoffsetoptionis2,anditslengthis4octets.

3 Router TherouteroptionspecifiesalistofIPaddressesforroutersontheclient’s subnet.Routersshouldbelistedinorderofpreference.

Thecodefortherouteroptionis3.Theminimumlengthfortherouteroptionis 4octets,andthelengthmustalwaysbeamultipleof4.

4 Timeserver ThetimeserveroptionspecifiesalistofRFC868timeserversavailabletothe client.Serversshouldbelistedinorderofpreference.

Thecodeforthetimeserveroptionis4.Theminimumlengthforthisoptionis4 octets,andthelengthmustalwaysbeamultipleof4.

5 Nameserver ThenameserveroptionspecifiesalistofIEN116nameserversavailabletothe client.Serversshouldbelistedinorderofpreference.

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Table1.StandardDHCPoptions (continued) Option

6 DomainName

Server

ThedomainnameserveroptionspecifiesalistofDomainNameSystem(STD 13,RFC1035)nameserversavailabletotheclient.Serversshouldbelistedin orderofpreference.

Thecodeforthedomainnameserveroptionis6.Theminimumlengthforthis optionis4octets,andthelengthmustalwaysbeamultipleof4.

7 Logserver ThelogserveroptionspecifiesalistofMIT-LCSUDPlogserversavailableto theclient.Serversshouldbelistedinorderofpreference.

Thecodeforthelogserveroptionis7.Theminimumlengthforthisoptionis4 octets,andthelengthmustalwaysbeamultipleof4.

8 Cookieserver ThecookieserveroptionspecifiesalistofRFC865cookieserversavailableto theclient.Serversshouldbelistedinorderofpreference.

Thecodeforthecookieserveroptionis8.Theminimumlengthforthisoption is4octets,andthelengthmustalwaysbeamultipleof4.

9 LPRserver TheLPRserveroptionspecifiesalistofRFC1179lineprinterserversavailable totheclient.Serversshouldbelistedinorderofpreference.

ThecodefortheLPRserveroptionis9.Theminimumlengthforthisoptionis4 octets,andthelengthmustalwaysbeamultipleof4.

10 Impressserver TheImpressserveroptionspecifiesalistofImagenImpressserversavailableto theclient.Serversshouldbelistedinorderofpreference.

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11 Resourcelocation server

ThisoptionspecifiesalistofRFC887ResourceLocationserversavailabletothe client.Serversshouldbelistedinorderofpreference.

Thecodeforthisoptionis11.Theminimumlengthforthisoptionis4octets, andthelengthmustalwaysbeamultipleof4.

12 Hostname Thisoptionspecifiesthenameoftheclient.Thenamemightormightnotbe qualifiedwiththelocaldomainname(seesection3.17forthepreferredwayto retrievethedomainname).SeeRFC1035forcharactersetrestrictions.

Thecodeforthisoptionis12,anditsminimumlengthis1.

13 Bootfilesize Thisoptionspecifiesthelengthin512-octetblocksofthedefaultbootimagefor theclient.Thefilelengthisspecifiedasanunsigned16-bitinteger.

Thecodeforthisoptionis13,anditslengthis2.

14 Meritdumpfile Thisoptionspecifiesthepath-nameofafiletowhichtheclient’scoreimage shouldbedumpedintheeventtheclientcrashes.Thepathisformattedasa characterstringconsistingofcharactersfromtheNVTASCIIcharacterset. Thecodeforthisoptionis14.Itsminimumlengthis1.

15 Domainname Thisoptionspecifiesthedomainnamethatclientshouldusewhenresolving hostnamesthroughtheDomainNameSystem.

Thecodeforthisoptionis15.Itsminimumlengthis1.

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17 Rootpath Thisoptionspecifiesthepath-namethatcontainstheclient’srootdisk.Thepath isformattedasacharacterstringconsistingofcharactersfromtheNVTASCII characterset.

18 Extensionspath Astringtospecifyafile,retrievableviaTFTP,whichcontainsinformationthat canbeinterpretedinthesamewayasthe64-octetvendor-extensionfieldwithin theBOOTPresponse,withthefollowingexceptions:

v Thelengthofthefileisunconstrained

v AllreferencestoTag18(thatis,instancesoftheBOOTPExtensionsPathfield)

withinthefileareignored.

19 IPforwarding ThisoptionspecifieswhethertheclientshouldconfigureitsIPlayerforpacket forwarding.Avalueof0meansdisableIPforwarding,andavalueof1means enableIPforwarding.

20 Non-Localsource routing

ThisoptionspecifieswhethertheclientshouldconfigureitsIPlayertoallow forwardingofdatagramswithnon-localsourceroutes.Avalueof0means disallowforwardingofsuchdatagrams,andavalueof1meansallow forwarding.

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21 Policyfilter Thisoptionspecifiespolicyfiltersfornon-localsourcerouting.Thefiltersconsist ofalistofIPaddressesandmaskswhichspecifydestination/maskpairswith whichtofilterincomingsourceroutes.

Anysourcerouteddatagramwhosenext-hopaddressdoesnotmatchoneofthe filtersshouldbediscardedbytheclient.

Thecodeforthisoptionis21.Theminimumlengthofthisoptionis8,andthe lengthmustbeamultipleof8.

22 Maximum

datagram reassemblysize

Thisoptionspecifiesthemaximumsizedatagramthattheclientshouldbe preparedtoreassemble.Thesizeisspecifiedasa16-bitunsignedinteger.The minimumvaluelegalvalueis576.

23 DefaultIPtimeto live

Thisoptionspecifiesthedefaulttime-to-livethattheclientshoulduseon outgoingdatagrams.TheTTLisspecifiedasanoctetwithavaluebetween1 and255.

24 PathMTUaging timeout

Thisoptionspecifiesthetimeout(inseconds)tousewhenagingPathMTU valuesdiscoveredbythemechanismdefinedinRFC1191.Thetimeoutis specifiedasa32-bitunsignedinteger.

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25 PathMTUplateau table

ThisoptionspecifiesatableofMTUsizestousewhenperformingPathMTU DiscoveryasdefinedinRFC1191.Thetableisformattedasalistof16-bit unsignedintegers,orderedfromsmallesttolargest.TheminimumMTUvalue cannotbesmallerthan68.

Thecodeforthisoptionis25.Itsminimumlengthis2,andthelengthmustbea multipleof2.

26 InterfaceMTU ThisoptionspecifiestheMTUtouseonthisinterface.TheMTUisspecifiedasa 16-bitunsignedinteger.TheminimumlegalvaluefortheMTUis68.

27 Allsubnetsare local

ThisoptionspecifieswhethertheclientcanassumethatallsubnetsoftheIP networktowhichtheclientisconnectedusethesameMTUasthesubnetofthat networktowhichtheclientisdirectlyconnected.Avalueof1indicatesthatall subnetssharethesameMTU.Avalueof0meansthattheclientshouldassume thatsomesubnetsofthedirectlyconnectednetworkmighthavesmallerMTUs. Thecodeforthisoptionis27,anditslengthis1.

28 Broadcastaddress Thisoptionspecifiesthebroadcastaddressinuseontheclient’ssubnet.Legal valuesforbroadcastaddressesarespecifiedinsection3.2.1.3ofRFC2132. Thecodeforthisoptionis28,anditslengthis4.

29 Performmask discovery

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30 Masksupplier Thisoptionspecifieswhethertheclientshouldrespondtosubnetmaskrequests usingICMP.Avalueof0indicatesthattheclientshouldnotrespond.Avalueof 1meansthattheclientshouldrespond.

31 Performrouter discovery

ThisoptionspecifieswhethertheclientshouldsolicitroutersusingtheRouter DiscoverymechanismdefinedinRFC1256.Avalueof0indicatesthattheclient shouldnotperformrouterdiscovery.Avalueof1meansthattheclientshould performrouterdiscovery.

32 Routersolicitation addressoption

Thisoptionspecifiestheaddresstowhichtheclientshouldtransmitrouter solicitationrequests.

33 Staticroute Thisoptionspecifiesalistofstaticroutesthattheclientshouldinstallinits routingcache.Ifmultipleroutestothesamedestinationarespecified,theyare listedindescendingorderofpriority.

TheroutesconsistofalistofIPaddresspairs.Thefirstaddressisthe destinationaddress,andthesecondaddressistherouterforthedestination. Thedefaultroute(0.0.0.0)isanillegaldestinationforastaticroute.

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34 Trailer encapsulation

Thisoptionspecifieswhethertheclientshouldnegotiatetheuseoftrailers(RFC 893)whenusingtheARPprotocol.Avalueof0indicatesthattheclientshould notattempttousetrailers.Avalueof1meansthattheclientshouldattemptto usetrailers.

35 ARPcachetimeout ThisoptionspecifiesthetimeoutinsecondsforARPcacheentries.Thetimeis specifiedasa32-bitunsignedinteger.

36 Ethernet

encapsulation

ThisoptionspecifieswhethertheclientshoulduseEthernetVersion2(RFC894) orIEEE802.3(RFC1042)encapsulationiftheinterfaceisanEthernet.Avalueof 0indicatesthattheclientshoulduseRFC894encapsulation.Avalueof1means thattheclientshoulduseRFC1042encapsulation.

37 TCPdefaultTTL ThisoptionspecifiesthedefaultTTLthattheclientshouldusewhensending TCPsegments.Thevalueisrepresentedasan8-bitunsignedinteger.The minimumvalueis1.

38 TCPkeep-alive interval

Thisoptionspecifiestheinterval(inseconds)thattheclientTCPshouldwait beforesendingakeepalivemessageonaTCPconnection.Thetimeisspecified asa32-bitunsignedinteger.Avalueofzeroindicatesthattheclientshouldnot generatekeepalivemessagesonconnectionsunlessspecificallyrequestedbyan application.

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39 TCPkeep-alive garbage

ThisoptionspecifieswhethertheclientshouldsendTCPkeepalivemessages withanoctetofgarbageforcompatibilitywitholderimplementations.Avalue of0indicatesthatagarbageoctetshouldnotbesent.Avalueof1indicatesthat agarbageoctetshouldbesent.

40 Network

informationservice domain

Thisoptionspecifiesthenameoftheclient’sNISdomain.Thedomainis formattedasacharacterstringconsistingofcharactersfromtheNVTASCII characterset.

41 Network

informationservers

ThisoptionspecifiesalistofIPaddressesindicatingNISserversavailabletothe client.Serversshouldbelistedinorderofpreference.

42 Networktime protocolservers option

ThisoptionspecifiesalistofIPaddressesindicatingNTPserversavailabletothe client.Serversshouldbelistedinorderofpreference.

44 NetBIOSover TCP/IPname server

TheNetBIOSnameserver(NBNS)optionspecifiesalistofRFC1001/1002 NBNSnameserverslistedinorderofpreference.

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45 NetBIOSover TCP/IPdatagram distributionserver

TheNetBIOSdatagramdistributionserver(NBDD)optionspecifiesalistofRFC 1001/1002NBDDserverslistedinorderofpreference.

Thecodeforthisoptionis45.Theminimumlengthoftheoptionis4octets,and thelengthmustalwaysbeamultipleof4.

46 NetBIOSover TCP/IPnodetype

TheNetBIOSnodetypeoptionallowsNetBIOSoverTCP/IPclientswhichare configurabletobeconfiguredasdescribedinRFC1001/1002.Thevalueis specifiedasasingleoctetwhichidentifiestheclienttypeasfollows:

Intheabovechart,thenotation’0x’indicatesanumberinbase-16(hexadecimal). Thecodeforthisoptionis46.Thelengthofthisoptionisalways1.

47 NetBIOSover TCP/IPscope

TheNetBIOSscopeoptionspecifiestheNetBIOSoverTCP/IPscopeparameter fortheclientasspecifiedinRFC1001/1002.

Thecodeforthisoptionis47.Theminimumlengthofthisoptionis1.

48 XWindowSystem Fontserver

ThisoptionspecifiesalistofXWindowSystemFontserversavailabletothe client.Serversshouldbelistedinorderofpreference.

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49 XWindowSystem displaymanager

ThisoptionspecifiesalistofIPaddressesofsystemsthatarerunningtheX WindowSystemDisplayManagerandareavailabletotheclient.

Addressesshouldbelistedinorderofpreference.

Thecodeforthethisoptionis49.Theminimumlengthofthisoptionis4,and thelengthmustbeamultipleof4.

51 IPaddresslease time

Thisoptionisusedinaclientrequest(DHCPDISCOVERorDHCPREQUEST)to allowtheclienttorequestaleasetimefortheIPaddress.Inaserverreply (DHCPOFFER),aDHCPserverusesthisoptiontospecifytheleasetimeitis willingtooffer.

Thetimeisinunitsofseconds,andisspecifiedasa32-bitunsignedinteger. Thecodeforthisoptionis51,anditslengthis4.

58 Renewal(T1)time value

Thisoptionspecifiesthetimeintervalfromaddressassignmentuntiltheclient transitionstotheRENEWINGstate.

Thevalueisinunitsofseconds,andisspecifiedasa32-bitunsignedinteger. Thecodeforthisoptionis58,anditslengthis4.

59 Rebinding(T2) timevalue

Thisoptionspecifiesthetimeintervalfromaddressassignmentuntiltheclient transitionstotheREBINDINGstate.

Thevalueisinunitsofseconds,andisspecifiedasa32-bitunsignedinteger. Thecodeforthisoptionis59,anditslengthis4.

62 NetWare/IP domainname

SpecifiestheNetware/IPdomainname.

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64 NISdomainname Thisoptionspecifiesthenameoftheclient’sNIS+domain.Thedomainis formattedasacharacterstringconsistingofcharactersfromtheNVTASCII characterset.

65 NISservers ThisoptionspecifiesalistofIPaddressesindicatingNIS+serversavailableto theclient.Serversshouldbelistedinorderofpreference.

66 Servername ThisoptionisusedtoidentifyaTFTPserverwhenthe’sname’fieldinthe DHCPheaderhasbeenusedforDHCPoptions.

67 Bootfilename Thisoptionisusedtoidentifyabootfilewhenthe’file’fieldintheDHCP headerhasbeenusedforDHCPoptions.

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69 SMTPservers TheSMTPserveroptionspecifiesalistofSMTPserversavailabletotheclient. Serversshouldbelistedinorderofpreference.

ThecodefortheSMTPserveroptionis69.Theminimumlengthforthisoption is4octets,andthelengthmustalwaysbeamultipleof4.

70 POP3server ThePOP3serveroptionspecifiesalistofPOP3availabletotheclient.Servers shouldbelistedinorderofpreference.

ThecodeforthePOP3serveroptionis70.Theminimumlengthforthisoption is4octets,andthelengthmustalwaysbeamultipleof4.

71 NNTPserver TheNNTPserveroptionspecifiesalistofNNTPavailabletotheclient.Servers shouldbelistedinorderofpreference.

ThecodefortheNNTPserveroptionis71.Theminimumlengthforthisoption is4octets,andthelengthmustalwaysbeamultipleof4.

72 WWWserver TheWWWserveroptionspecifiesalistofWWWavailabletotheclient.Servers shouldbelistedinorderofpreference.

ThecodefortheWWWserveroptionis72.Theminimumlengthforthisoption is4octets,andthelengthmustalwaysbeamultipleof4.

73 Fingerserver TheFingerserveroptionspecifiesalistofFingeravailabletotheclient.Servers shouldbelistedinorderofpreference.

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74 IRCserver TheIRCserveroptionspecifiesalistofIRCavailabletotheclient.Servers shouldbelistedinorderofpreference.

ThecodefortheIRCserveroptionis74.Theminimumlengthforthisoptionis 4octets,andthelengthmustalwaysbeamultipleof4.

75 StreetTalkserver TheStreetTalkserveroptionspecifiesalistofStreetTalkserversavailabletothe client.Serversshouldbelistedinorderofpreference.

ThecodefortheStreetTalkserveroptionis75.Theminimumlengthforthis optionis4octets,andthelengthmustalwaysbeamultipleof4.

76 STDAserver TheStreetTalkDirectoryAssistance(STDA)serveroptionspecifiesalistofSTDA serversavailabletotheclient.Serversshouldbelistedinorderofpreference. ThecodefortheStreetTalkDirectoryAssistanceserveroptionis76.The minimumlengthforthisoptionis4octets,andthelengthmustalwaysbea multipleof4.

77 Userclass Specifiestheclassnameofwhichthehostisamember.Youmusthave previouslydefinedthisclasstotheDHCPserverduringDHCPserver configuration.

78 Directoryagent SpecifiestheIPaddressofthedirectoryagentifclientsuseServiceLocation Protocoltotransactmessages.

79 Servicescope SpecifiesthescopeofthedirectoryagentthatusesServiceLocationProtocolto respondtoservicerequestmessages.

80 Namingauthority SpecifiesthenamingauthorityforthedirectoryagentifclientsuseService LocationProtocoltotransactmessages.Thenamingauthorityspecifiesthe syntaxforschemesthatareusedinURLs.

Related information

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Example:

Simple

DHCP

subnet

Thisexampleexplains howtosetupa SystemimodelasaDynamic HostConfigurationProtocol (DHCP)serverina simpleLAN withfourPCclientsanda LAN-basedprinter.

Inthisexample,theSystemimodel actsasaDHCPserverfor the10.1.1.0IPsubnet.Itisconnected to theLANwithits10.1.1.1interface.

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subnet10.1.1.0hashundredsofclients, anadministratoronlyneedstocreateasingleDHCPpolicyon thesystem.ThispolicydistributesIPinformationtoeachclient.

WhenPCclientssend outtheirDHCPDISCOVERsignals,theserverrespondswiththeappropriateIP information.Inthisexample,thecompanyalsohasa LAN-basedprinterthatobtains itsIPinformation fromtheDHCPservertoo.ButbecausePCclientsdependontheprinter’sIPaddressremainingthe same,thenetworkadministratorshouldaccountforthatintheDHCPpolicy.Onesolutionistoassigna constantIPaddress totheprinter.TheDHCPserverenablesyoutodefineaclient,liketheLANprinter, intheDHCPpolicybyitsMACaddress.IntheDHCPclientdefinition,youcanthen assignspecific values,suchasIPaddressesand routeraddresses,totheintendedclient.

Fora clienttocommunicatewith aTCP/IPnetwork,itrequiresat leastanIPaddressandsubnet mask. TheclientswillgettheirIPaddressfromtheDHCPserver,andtheDHCPserverpassesadditional configurationinformation(forexample,theirsubnet mask)usingtheconfigurationoptions.

Planning

the

DHCP

setup

for

a

simple

LAN

Table2.Globalconfigurationoptions(appliestoallclientsservedbytheDHCPserver)

Object Value

Configurationoptions option1:Subnetmask 255.255.255.0 option6:Domainnameserver 10.1.1.1

option15:Domainname mycompany.com

Subnetaddressesnotassignedbythesystem 10.1.1.1(Domainnameserver) IsthesystemperformingDNSupdates? No

IsthesystemsupportingBOOTPclients? No

Table3.SubnetforPCs

Subnetname SimpleSubnet

Addressestomanage 10.1.1.2-10.1.1.150

Leasetime 24hours(default)

Configuration options Inherited options

Options from Global configuration

Table4.Clientforprinter

ClientName LANPrinter

ClientAddress 10.1.1.5

Configuration options

(31)

“Example: DHCPandmultihoming”onpage27

Thisexampleexplainshowtoset upaSystemimodelasa DynamicHostConfigurationProtocol (DHCP)serverforaLAN thatisconnectedtotheInternet byanInternet router.

Example:

Multiple

TCP/IP

subnets

Thisexampleexplains howtosetupa SystemimodelasaDynamic HostConfigurationProtocol (DHCP)serverwith twoLANsconnectedbyaDHCP-enabledrouter.

(32)

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subnet.Ataminimum,thedifferencesbetweenthesubnetsare theirIPsubnetsandrouteraddresses.The dataentrysubnetneedstoreceivea routeraddressof10.1.2.2tocommunicatewiththeofficesubnet.

Planning

the

DHCP

setup

for

multiple

LANs

option1:Subnetmask 255.255.255.0 option6:Domainnameserver 10.1.1.1

Subnetaddressesnotassignedbythesystem 10.1.1.1(Domainnameserver) IsthesystemperformingDNSupdates? No

Table6.SubnetforOfficeclients

Subnetname Office

option3:Router 10.1.1.2

inheritedoptions OptionsfromGlobalconfiguration Subnetaddressesnotassignedbyserver 10.1.1.2(Router)

Table7.SubnetforDataEntryclients

Subnetname DataEntry

Inheritedoptions OptionsfromGlobalconfiguration Subnetaddressesnotassignedbyserver 10.1.2.2(Router)

“Example: SimpleDHCPsubnet”onpage23

Thisexampleexplainshowtoset upaSystemimodelasa DynamicHostConfigurationProtocol (DHCP)serverinasimple LANwithfourPCclients andaLAN-basedprinter.

Example:

DHCP

and

multihoming

Thisexampleexplains howtosetupa SystemimodelasaDynamic HostConfigurationProtocol (DHCP)serverfora LANthatisconnectedtotheInternetbyanInternetrouter.

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addresstocommunicatewiththeInternet.WhenmultipleIPaddressesare assignedtothesame adapter, thesystemismultihoming.

Note: Althoughthisisa feasiblewaytoconnectyournetworktotheInternet,itisnotthemostsecure

way. Itsuitsthepurposesofthis DHCPexample,butyoushouldconsider thesecurityimplications whenyouconfigureyourown DHCPserver.

TheDHCPsetup musttakeintoaccountthattheSystemimodelisknownbytwodifferentIPaddresses.

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Butitispossiblethatthepacket canactuallyget markedwiththe192.168.1.1address(theoneconnected totheInternet).Ifthepacket isreceivedonthe192.168.1.1interface,your dataentryclient doesnot receiveanyIPinformation.

TosetupDHCPinthissituation,youneedtonotonlycreatethedataentryDHCPsubnet,butalso createasubnet fortheInternet network.TheInternet policyconsistsofa subnetwith noavailable

addresses.Theeasiestwaytodo thisistodefinethesubnetwith atleastoneIPaddress(like 192.168.1.1), thenexcludethatsame IPaddress.Withthetwosubnetsdefined, younow combinethetwo(or more) subnetsintoasubnetgroup.IftheDISCOVERpacketgetsmarkedwith the192.168.1.1 interface,thedata entrysubnetwillstillissuevalidIPinformation.

Tomakethisscenariowork,thedataentrysubnet mustpassitsclientstheirrouteraddressforaccessto theInternet.Inthis case,therouteraddressistheSystemiinterface of10.1.1.1.Youmustalso setIP datagramforwardingtoonforthetwointerfacestoroutepacketstoeachother. Thisexampleuses reservedIPaddressestorepresentbothinternalandexternalIPaddresses.Ifyournetworkmatchesthis scenario,youalsoneedtousenetworkaddress translation(NAT)foryour dataentryclientsto

communicatewith theInternet.

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Planning

the

DHCP

setup

for

multihoming

IsthesystemperformingDNSupdates? No IsthesystemsupportingBOOTPclients? No

Table9.SubnetforDataEntryclients

Subnetname DataEntry

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Table9.SubnetforDataEntryclients (continued)

Subnetaddressesnotassignedbyserver 10.1.1.1(Router,DNSserver)

Table10.SubnetforInternetclients(emptySubnet)

Subnetname Internet

Subnetaddressesnotassignedbyserver 192.168.1.1(AllIPaddressesavailable)

Table11.SubnetgroupforallincomingDISCOVERpackets

SubnetGroupName Multihomed

Subnetsincludedingroup Subnet Internet Subnet DataEntry

Other

setup

v SetIPDatagramforwardingto’on’forthetwointerfaces

v SetupNATfortheDataEntryclients Related reference

“Example: SimpleDHCPsubnet”onpage23

Thisexampleexplainshowtoset upaSystemimodelasa DynamicHostConfigurationProtocol (DHCP)serverinasimple LANwithfourPCclients andaLAN-basedprinter.

Example:

DNS

and

DHCP

on

the

same

System

i

Thisexampleexplains howtosetupa SystemimodelasaDynamic HostConfigurationProtocol (DHCP)serverwith dynamicDomainNameSystem(DNS)updatesonasimple LAN.

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Previousversionsof DHCPandDNSwere independentofeachother.IfDHCPassignedanewIP addresstoa client,theDNSrecordshadtobe manuallyupdatedbytheadministrator.Inthisexample,if thegraphicsfileserver’s IPaddress changesbecauseitisassignedbyDHCP, thenitsdependentclients areunabletomapanetworkdrivetoitshostnamebecausetheDNSrecordscontainthefileserver’s previousIPaddress.

WiththecurrentDNSserver,youcandynamically updateyour DNSrecordsin conjunctionwith

intermittentaddresschanges throughDHCP.For example,whenthegraphicsfileserverrenewsitslease andisassignedanIPaddressof10.1.1.250bytheDHCPserver,theassociatedDNSrecordsare updated dynamically.ThisallowstheotherclientstoquerytheDNSserverforthegraphicsfileserverbyitshost namewithoutinterruption.

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Note: IfyousetDHCPtoupdateonlyPTRrecords,youmustconfigureDNStoallowupdatesfrom

clients sothateachclientcanupdateitsArecord.NotallDHCPclientssupportmaking theirown Arecordupdaterequests.Consultthedocumentationforyour clientplatformbeforechoosing this method.

ToenableDNSupdates,youmustcreatea DNSkeyforyourDHCPserver.TheDNSkeyauthorizesthe DHCPservertoupdatetheDNSrecordsbased onIPaddressesithasdistributed.Then,in theDHCP configuration,choosethescopelevelwhereyouwantDNSupdatestooccur.For example,if youwantall subnetstoperformDNSupdates,settheupdatesattheGloballevel.Ifyouwantonlyonesubnetto performupdates,thenset onlythatsubnet toupdate.

Planning

the

DHCP

setup

when

using

Dynamic

DNS

IsthesystemperformingDNSupdates? Yes--BothAandPTRrecords IsthesystemsupportingBOOTPclients? No

Table13.SubnetforNetworkRing

Subnetname NetworkSubnet

Inheritedoptions OptionsfromGlobalconfiguration

Other

setup:

AuthorizeDHCPtosendupdatestoDNS.RefertoExample:DNSand DHCPonthesameSystemiin theDNStopiccollection.

Example:

DNS

and

DHCP

on

different

System

i

models

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Planning

the

DHCP

setup

when

using

Dynamic

DNS

(41)

Installi5/OSDomainNameSystem(Option31)ontheSystemi modelthatwillberunningDHCP, in thiscase,mysystemi2. Thisoption containsthedynamicupdateAPIthatmanagestheresourcerecord updateprocess.Refer toDNSsystemrequirementsforinstallationinstructions.

AuthorizingDHCPtosendupdatesto DNS

YoumustauthorizetheDHCPservertosend updatestotheDNSserver.Youcaneitherrepeat the processofdefiningtheDynamicUpdateKey, oryoucansendthefileandplaceitintheappropriate directorypath.

TocreateaDynamicUpdate KeyonbothSystemimodels,followthesesteps: 1. IniSeriesNavigator,expandyoursystem→ Network→ Servers→ DNS.

2. Intheleftpane,right-click DNSandselectManageDynamicUpdateKeys.

3. On theManagingDynamic UpdateKeyspage,selectAdd.

4. On theAddDynamicUpdate Keyspage,completethefollowingfields:

v Keyname:Specify thenameforthekey,forexamplemycompany.key.Thekeynamemustbe

dot-terminated.

v Dynamicupdatezones:Specifythezonenamesforwhichthiskeywillbe valid.Youcanspecify

morethanonezone. v

Generatekey:Selectthemethod thatyouwanttousetogeneratea secretkey.

5. RepeattheprecedingstepssothatthesamekeyisdefinedonboththeSystemimodelrunningDNS

and thesystemrunningDHCP.

DomainNameSystemrequirements Related information

Update DNSAPI

Example:

PPP

and

DHCP

on

a

single

System

i

Thisexampleexplains howtosetupa SystemimodelasaDynamic HostConfigurationProtocol (DHCP)serverfora LANanda remotedial-inclient.

(42)

Fortheremoteemployeetosuccessfullybecomepartofthecompany’snetwork,theSystemimodelmust usea combinationofRemoteAccessServicesandDHCP.TheRemoteAccessServicesfunction createsthe dial-incapabilityfortheSystemimodel.Ifsetupproperly,aftertheclientestablishes thedial-in

connection,thePPPservertellstheDHCPservertodistribute TCP/IPinformationtotheremoteclient. Inthisexample,asingleDHCPsubnetpolicycoversboththeon-sitenetworkclientsandthedial-in clients.

IfyouwantyourPPPprofiletodefertotheDHCPforIPdistribution,youmustdo sointhePPPprofile. IntheTCP/IPsettingsofthereceiverconnection profile,youmust settheremoteIPaddressassignment methodfromFixedtoDHCP.Toallowthedial-inclients tocommunicatewith othernetworkclients,like theLANprinter,youmustalso allowIPforwardingintheTCP/IPsettingsoftheprofileand theTCP/IP configuration(stack)properties. IfyouonlysetIPforwardingoninthePPPprofile, theSystemi model willnotpasstheIPpackets.Youmustset IPforwarding oninboththeprofileandthestack.

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Planning

the

DHCP

setup

for

on-site

and

PPP

clients

option15:Domainname mycompany.com IsthesystemperformingDNSupdates? No

Table15.Subnetforbothon-siteanddial-inclients

SubnetName MainNetwork

Inheritedoptions OptionsfromGlobalconfiguration

Subnetaddressesnotassignedbyserver 10.1.1.1(Localinterfaceaddressspecifiedinthe TCP/IPSettingsoftheReceiverConnection ProfilepropertiesiniSeriesNavigator)

Other

setup

v SettheRemoteIPaddressmethod toDHCPinthePPPreceiverconnectionprofile.

1. EnableDHCPWANclientconnectionwith aDHCPserverorrelayconnection usingtheServices

menuitemforRemoteAccessServicesiniSeriesNavigator.

2. SelecttoUseDHCPfortheIPaddressassignmentmethodundertheTCP/IPSettingsPropertiesof

theReceiverConnectionProfileiniSeriesNavigator. v

Allowremotesystemtoaccessothernetworks(IPforwarding)undertheTCP/IPSettingsPropertiesof

theReceiverConnectionProfileiniSeries Navigator.

v EnableIPdatagramforwardingundertheSettingsPropertiesoftheTCP/IPConfigurationiniSeries

Navigator.

“Example: DHCPandPPPprofileondifferentSystemimodels”

Thisexampleexplainshowtoset uptwoSystemimodels asthenetworkDynamicHost

ConfigurationProtocol(DHCP)serverandaBOOTP/DHCPrelayagentfortwoLANsand remote dial-in clients.

Example:

DHCP

and

PPP

profile

on

different

System

i

models

Thisexampleexplains howtosetuptwoSystemimodelsasthenetworkDynamicHostConfiguration Protocol(DHCP)serverand aBOOTP/DHCPrelayagentfortwoLANsand remotedial-inclients. TheexampleaboutPPPandDHCPona singleSystemimodelshowshowtousePPPandDHCPona singlesystemtopermitdial-inclients accesstoa network.Ifyouareconcernedwith thephysical layout |

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Theremotedataentryclientsdial intotheSystemi PPPserver.ThePPPprofileonthatservermust have aremote IPaddress methodofDHCP,suchasintheexampleaboutPPPandDHCPona singleSystemi modelaswellasIPforwardinginthePPPprofileandintheTCP/IPstackproperties.Furthermore, becausethisserverisactingasaDHCPrelayagent,theBOOTP/DHCPrelayagentmustbe on.This

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dial-inordirectlyattachednetworkclients.Thedataentryclientsalso needarouteraddress(option 3)of 10.1.2.1tocommunicatewiththeworknetwork,and theSystemi DHCPservermustalso haveIP forwardingenabled.

Also,theLocalInterfaceIPaddress inthePPPprofilemustbe anIPaddressthatfallswithin thesubnet definitionintheDHCPserver.Inthisexample,thePPPprofileLocalInterfaceaddressshouldbe 10.1.2.2. Thisaddress shouldalso beexcludedfromtheDHCPserver’saddresspoolsothatit isnotassignedtoa DHCPclient.TheLocalInterfaceIPaddressmustbe anaddresstowhichtheDHCPservercansend replypacketsto.

Planning

the

DHCP

setup

for

DHCP

with

a

DHCP

relay

agent

option15:Domainname mycompany.com IsthesystemperformingDNSupdates? No

Table17.SubnetforWorkNetwork

Subnetname WorkNetwork

Inheritedoptions OptionsfromGlobalconfiguration Subnetaddressesnotassignedbyserver none

Table18.SubnetforDataEntryNetwork

SubnetName DataEntry

Inheritedoptions OptionsfromGlobalconfiguration Subnetaddressesnotassignedbyserver 10.1.2.1 (Router)

10.1.2.15 (Remote Data Entry client’s local interface IP address) 10.1.2.14 (Remote Data Entry client’s local interface IP address)

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1. EnableDHCPWANclientconnectionwith aDHCPserverorrelayconnection usingtheServices

menuitemforRemoteAccessServicesiniSeriesNavigator

2. SelecttoUseDHCPfortheIPaddressassignmentmethodundertheTCP/IPSettingsPropertiesof

theReceiverConnectionProfileiniSeriesNavigator

v Allowremotesystemto accessothernetworks(IPforwarding)undertheTCP/IPSettingsPropertiesof

theReceiverConnectionProfileiniSeries Navigator(toallowtheremoteclientstocommunicatewith thedataentrynetwork)

v EnableIPdatagramforwardingundertheSettingsPropertiesoftheTCP/IPConfigurationiniSeries

Navigator(toallowtheremoteclients tocommunicatewith thedataentrynetwork)

“Example: PPPand DHCPonasingle Systemi”onpage35

Thisexampleexplainshowtoset upaSystemimodelasa DynamicHostConfigurationProtocol (DHCP)serverforaLAN andaremote dial-inclient.

Planning

for

DHCP

SettingupDynamicHostConfigurationProtocol(DHCP)canbe atime-consumingand error-prone processifyouhavenottakenthetimetoplanhowyour DHCPservershouldbeconfigured.By taking timetothinkaboutyour networksetup andsecurityconcernsinadvance,youcanconfigureyour DHCP servermoreefficiently.

ConsidersecurityandnetworktopologyimplicationsbeforeyouconfigureDHCPonyour network.

“ConfiguringDHCP”onpage43

Here areinstructionsforsettingupyourDHCPserverandclients,andfor configuringDHCPtosend dynamicupdatestoDomainNameSystem(DNS).

Security

considerations

TheDHCPprotocolisnotcapableofverifyingthatclientsrequestingIPaddressesareauthorizedtodo so.

BecauseofthenatureofDHCP’sinteractionwith thenetwork, itisimportantthatyousecureyour Systemimodelfromoutsideclients.Ifyour DHCPserverisonaSystemimodelthatispartofa trusted internalnetwork, youmight beabletouseIPfilteringandnetworkaddresstranslationtofurthersecure itfromanyunauthorizedparties.Ifyour DHCPserverisonaSystemimodelthatisattachedtoan untrustednetwork,suchastheInternet, referto theSystemiand Internetsecuritytopic.

IPfilteringandnetworkaddresstranslation Security

Network

topology

considerations

(47)

apiece ofscrappaper.Youshouldinclude alloftheLANs,thedevicesthatconnecttheLANs,andtheIP addressesfordevicesandclients (forexample,aprinter)thatneedadefinedIPaddress.Youmight want tolookatsomeoftheDHCPexamples tohelpyousketchoutyournetworktopology.

Determining

the

number

of

DHCP

servers

Evenwith acomplexnetwork, youcanstillmanage allofyournetworkclients usingonlyoneDHCP server.Dependingonyour networktopology, youmight needtosetupa fewDHCP/BOOTPrelay agentsorenableyourrouterstoforwardDHCPpacketsto makeitwork.

UsingonlyoneDHCPserverforyour entirenetworkwillcentralizehostconfigurationmanagementfor allofyourclients. However,therearecaseswhereyoumightwanttoconsiderusingmultipleDHCP serversinyour network.

Toavoida singlepointoffailure,youcanconfiguretwoormoreDHCPserverstoservethesamesubnet. Ifoneserverfails,theothercancontinuetoservethesubnet.EachoftheDHCPservers mustbe

accessibleeitherbydirectattachmenttothesubnetorbyusingaDHCP/BOOTPrelayagent.

BecausetwoDHCPserverscannotservethesame addresses,addresspoolsdefinedfora subnetmustbe uniqueacrossDHCPservers.Therefore,whenusingtwoormore DHCPserverstoservea particular subnet,thecompletelistofaddressesforthatsubnetmust bedividedamongtheservers.Forexample, youcanconfigureoneserverwithan addresspoolconsistingof 70%oftheavailableaddressesforthe subnetandtheotherserverwithan addresspoolconsistingoftheremaining30%oftheavailable addresses.

UsingmultipleDHCPserversdecreasestheprobabilityofhavinga DHCP-relatednetworkaccessfailure, butitdoesnotguaranteeagainstit.Ifa DHCPserverfora particularsubnetfails,theotherDHCPserver mightnotbeable toservicealltherequestsfromnewclients,whichmight,forexample,exhaustthe server’slimited poolofavailable addresses.

Ifyouare consideringmultiple DHCPservers,rememberthatmultipleDHCPserverscannotshare anyof thesameaddresses.IfyouusemorethanoneDHCPserverinyournetwork,eachservermust be

configuredwiththeirown uniqueIPaddressranges.

Identifying

the

IP

addresses

that

your

DHCP

server

should

manage

Usingyour networktopology, youshouldstartdocumenting whichnetworkaddressrangesyouwantthe DHCPservertomanage.Youshouldidentifywhichdevices havea manuallyconfiguredIPaddresses (forexample,therouter’s IPaddress) thatyouwanttoexcludefromtheDHCP’saddresspool.

Inaddition,youwillwanttoconsider whethertheseaddressesshouldbe assigneddynamicallybythe DHCPserverorif youwanttoassigna specificIPaddresstocertainclients.Youmightwanttoreservea specificaddress andconfigurationparametersfora specificclientona particularsubnet,suchasa file server.Or, youmight wanttomapallofyour clientstoa specificIPaddress.RefertoDHCPclient supportformoreinformationaboutassigningIPaddressesdynamicallyversusstatically.

Determining

the

lease

time

for

the

IP

addresses

(48)

Supporting

BOOTP

clients

Ifyouare currentlyusingaBOOTPserver,considerthattheDHCPservercanreplacetheBOOTPserver onyournetworkwithlittleornoimpacttoyourBOOTPclients.Therearethreeoptionsforyouifyou haveBOOTPclients currentlyonyour network.

TheeasiestoptionistoconfigureyourDHCPservertosupport BOOTPclients.WhenyouuseDHCPto supportyour BOOTPclients,eachBOOTPclientisessentiallybeingmappedtoasingle IPaddress,and thataddressisthereforenotre-usablebyanotherclient.Theadvantage,however,of usingDHCPinthis caseisthatthereisnoneedtoconfigurea one-to-onemappingofBOOTPclientstoIPaddresses.The DHCPserverwillstilldynamicallyassignanIPaddressestotheBOOTPclientfromtheaddresspool. AftertheIPaddressisassignedtotheBOOTPclient,itispermanentlyreservedforusebythatclient untilyouexplicitlydeletetheaddress reservation.Thisisagoodoptionif youhavea largenumberof BOOTPclients inyournetwork.

Anotheroptionistomigrateyour BOOTPserverconfigurationtotheDHCPserver.ADHCPclient will becreatedforeachBOOTPclientlistedintheBOOTPserverconfiguration.Inthisoption,itis

recommendedthatyoureconfigureyour clientstobe DHCPclients.However, whenyoumigrate your BOOTPconfigurationtoDHCP, theDHCPaddressassignmentswillworkforeither aBOOTPorDHCP client.Thismight bea goodoption totransitionyour BOOTPclients toDHCP.YourBOOTPclients will stillbe supportedduring theprocess ofreconfiguringthemtoDHCP.

Eventually,youmight wanttodo thethirdoption:changeeachBOOTPclienttoDHCPand configure DHCPtodynamically assignthemaddresses.Essentially,thisoption removesBOOTPentirelyfromthe network.

Identifying

the

configuration

information

for

the

network

clients

Usingyour networktopology layout,youcanclearlyseethedevices(forexample,routers)thatmustbe identifiedintheDHCPconfiguration. Inaddition,youshouldidentifyotherservers inyournetwork, suchastheDomainNameSystem(DNS)server,thatyourclients mightneed toknowabout.Youcan eitherspecifythisinformationfortheentirenetwork,a specificsubnet,ora specificclientregardlessof thesubnet.

Ifyouhavedevicesthatapplytomanyclients,youwillwanttospecifythematthehighestlevelpossible (forexample,attheGloballevelfortheentirenetwork,orat thesubnetlevelfora specificsubnet). This willminimizethechangesyouwillneed tomaketotheDHCPconfigurationwhenthedevicechanges.If youhavespecifiedthesamerouter, forexample,foreveryclientinyournetwork, youneedtochangethe configurationforeveryclientwhentherouterhaschanged.However,ifyouhavespecifiedtherouterat thegloballevel(alloftheclientswillinheritthisconfigurationinformation),youonlyneedtochangethe informationonceand theinformationischangedforall clients.

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DynamicDNS,theclients willnotnoticeanyinterruptionor changesintheDNSservicewhenyou switchovertoDHCP.For moreinformationaboutusingDHCPwithyour DNSserver,refertoDynamic updates.

Ifyouare notcurrentlyusingaDNSserver,youmight wanttoconsider addingaDNSserverwhenyou addtheDHCPserver.YoucanreadtheDNStopictofindoutmoreaboutDNSbenefitsandrequirements intheinformationcenter.

Using

DHCP

for

your

remote

clients

Ifyouhaveanyremoteclientsthatconnecttoyour networkusingPPP,youcanset upDHCPto dynamicallyassignanIPaddresstothemwhentheyconnecttothenetwork.Toseesomeexamplesof networkswherethismight beuseful,see“Example: PPPandDHCPona singleSystemi”onpage35or “Example:DHCPand PPPprofileondifferentSystemimodels”onpage37.Theseexamplesalso explain howtoset upthenetworktousePPPand DHCPtogetherforyour remoteclients.

“Examples:DHCP”onpage22

By reviewingdiagrams andexamplesofhow differentnetworksaresetup,youcandeterminewhich isthebestchoiceforyourinstallation.

“DHCPclientsupport”onpage6

ADHCPserverenablesyoutomanage eachclientinyournetworkindividually,ratherthan managingalloftheclientsasa largegroup(subnet).

“Leases”onpage3

WhenDHCPsendsconfigurationinformationtoaclient,theinformationissentwith aleasetime. ThisisthelengthoftimethattheclientcanusetheIPaddressithasbeenassigned.Thedurationof theleasetimecanbechangedaccording toyourspecific requirement.

“BOOTP”onpage7

TheBootstrapProtocol(BOOTP)isahostconfigurationprotocolthatwasusedbeforetheDynamic HostConfigurationProtocol(DHCP)was developed.BOOTPsupportisasubsetofDHCP.

“Dynamicupdates”onpage7

ADynamicHostConfigurationProtocol(DHCP)servercanbe configuredtoworkwitha Domain Name System(DNS)servertodynamicallyupdatetheclientinformationintheDNSwhenDHCP assignstheclientanIPaddress.

DomainNameSystem

Configuring

DHCP

Hereareinstructions forsettingupyour DHCPserverandclients, andforconfiguringDHCPtosend dynamicupdatestoDomainNameSystem(DNS).

“PlanningforDHCP” onpage40

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Configuring

or

viewing

the

DHCP

server

YoucanusetheDHCPserverconfigurationfunctiontocreatea newDHCPconfigurationorview the existingDHCPconfiguration.

ToaccesstheDHCPserverconfiguration, followthese steps:

1. IniSeriesNavigator,expandyoursystem→ Network→ Servers→TCP/IP→ DHCP.

2. Right-clickDHCP,andthenselectConfiguration.

Ifyouare creatinganew DHCPconfiguration,youwilluseawizardthathelpsyousetuptheDHCP server.Thiswizardasksyousomeof thebasicconfigurationquestionsand stepsyouthroughtheprocess ofcreatinga subnet.Afteryouhavecompletedthewizard,youcanchangeand improvethe

configurationtoyournetwork’sneeds.

IfyourDHCPserverisalreadyconfigured,theDHCPserverconfigurationfunctionwilldisplaythe currentconfiguration,includingallofthesubnetsandclientsthatcanbe managedfromtheDHCPserver andtheconfigurationinformationthatwillbesent totheclients.

CreateashortcuttotheDHCPconfigurationwindow

Followthesestepsifyoulookat theDHCPconfigurationfrequentlyand wanttocreatea shortcuttothe DHCPconfigurationwindowonyour desktop.

2. Right-clickDHCP,andthenselectCreateShortcut.

Starting

or

stopping

the

DHCP

server

AftertheDHCPserverisconfigured,youcanstart orstoptheDHCPserver.

2. Right-clickDHCP,andthenselectStartorStop.

Configuring

the

DHCP

server

to

be

started

automatically

YoucanfollowthesestepstoconfiguretheDHCPservertobe startedautomatically. 1. IniSeriesNavigator,expandyoursystem→ Network→ Servers→TCP/IP→ DHCP.

2. Right-clickDHCP,andthenselectConfiguration.

3. Right-clickDHCPServerandselectProperties.

4. ChecktheStartwhenTCP/IP isstartedcheckbox.

5. ClickOK.

Accessing

the

DHCP

server

monitor

TheDynamicHostConfigurationProtocol(DHCP)servermonitor isprovidedto monitoractivelease informationforanIBM® _System_i _DHCP_server._You_can_use_this_graphical_interface_to_view _which_IP

How To Plan Out Your Own Version Of Hpl (Dhcp) On A Network With A Network (Dns) On Your Network (Dhpl) On An Ipad Or Ipad On A Pc Or Ipa On A Server On A

System

i

Networking

Dynamic

Host

Configuration

Protocol

Version

5

Release

4

System

i

Networking

Dynamic

Host

Configuration

Protocol

Version

5

Release

4

Contents

Dynamic

Host

Configuration

Protocol

.

. 1

Appendix.

Notices

.

.

.

.

.

.

.

.

.

. 55

Dynamic

Host

Configuration

Protocol

Printable

PDF

Saving

PDF

files

Downloading

Adobe

Reader

DHCP

concepts

DHCP

client/server

interaction

Leases

Lease

renewal

Determining

lease

duration

Relay

agents

and

routers

DHCP

client

support

BOOTP

Dynamic

updates

DHCP

options

lookup

Example:

Simple