RFC3633.docx
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RFC3633.docx
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RFC3633
NetworkWorkingGroupO.Troan
RequestforComments:
3633R.Droms
Category:
StandardsTrackCiscoSystems
December2003
IPv6PrefixOptionsfor
DynamicHostConfigurationProtocol(DHCP)version6
StatusofthisMemo
ThisdocumentspecifiesanInternetstandardstrackprotocolforthe
Internetcommunity,andrequestsdiscussionandsuggestionsfor
improvements.Pleaserefertothecurrenteditionofthe"Internet
OfficialProtocolStandards"(STD1)forthestandardizationstate
andstatusofthisprotocol.Distributionofthismemoisunlimited.
CopyrightNotice
Copyright(C)TheInternetSociety(2003).AllRightsReserved.
Abstract
ThePrefixDelegationoptionsprovideamechanismforautomated
delegationofIPv6prefixesusingtheDynamicHostConfiguration
Protocol(DHCP).Thismechanismisintendedfordelegatingalong-
livedprefixfromadelegatingroutertoarequestingrouter,across
anadministrativeboundary,wherethedelegatingrouterdoesnot
requireknowledgeaboutthetopologyofthelinksinthenetworkto
whichtheprefixeswillbeassigned.
TableofContents
1.Introduction........................2
2.DHCPv6specificationdependency..............3
3.Terminology........................3
4.Requirements........................3
5.ModelandApplicability..................3
5.1.Examplenetworkarchitecture.............4
6.IdentityAssociationforPrefixDelegation.........5
7.OverviewofDHCPwithPrefixDelegation..........6
8.InterfaceSelection....................7
9.IdentityAssociationforPrefixDelegationOption.....7
10.IA_PDPrefixoption....................9
11.DelegatingRouterSolicitation...............11
11.1.Requestingrouterbehavior..............11
11.2.Delegatingrouterbehavior..............11
12.Requestingrouterinitiatedprefixdelegation.......12
Troan&DromsStandardsTrack[Page1]
RFC3633IPv6PrefixOptionsforDHCPv6December2003
12.1.Requestingrouterbehavior..............12
12.2.DelegatingRouterbehavior..............14
13.PrefixDelegationreconfiguration.............15
13.1.DelegatingRouterbehavior..............15
13.2.RequestingRouterbehavior..............15
14.Relayagentbehavior....................15
15.SecurityConsiderations..................16
16.IANAConsiderations....................16
17.IntellectualPropertyStatement...............17
18.References.........................17
18.1.NormativeReferences.................17
18.2.InformativeReferences................17
19.Acknowledgements......................18
20.Authors'Addresses.....................18
21.FullCopyrightStatement..................19
1.Introduction
ThisdocumentdescribesnewoptionsforDynamicHostConfiguration
Protocol(DHCP)thatprovideamechanismforthedelegationofIPv6
prefixes[1].Throughtheseoptions,adelegatingroutercan
delegateprefixestoauthorizedrequestingrouters.
Theprefixdelegationmechanismdescribedinthisdocumentis
intendedforsimpledelegationofprefixesfromadelegatingrouter
torequestingrouters.Itisappropriateforsituationsinwhichthe
delegatingrouterdoesnothaveknowledgeaboutthetopologyofthe
networkstowhichtherequestingrouterisattached,andthe
delegatingrouterdoesnotrequireotherinformationasidefromthe
identityoftherequestingroutertochooseaprefixfordelegation.
Forexample,theseoptionswouldbeusedbyaserviceproviderto
assignaprefixtoaCustomerPremiseEquipment(CPE)deviceacting
asarouterbetweenthesubscriber'sinternalnetworkandtheservice
provider'scorenetwork.
Manyapplicationsexpectstableaddresses.Eventhoughthis
mechanismmakesautomaticrenumberingeasier,itisexpectedthat
prefixeshavealonglifespan.Duringrenumberingitisexpected
thattheoldandthenewprefixco-existforsometime.
Thedesignofthisprefixdelegationmechanismmeetstherequirements
forprefixdelegationinRequirementsforIPv6prefixdelegation[6].
NotethatthisuseofDHCPisnotboundtotheassignmentofIP
addressesorotherconfigurationinformationtohosts,andthatno
mechanismiscurrentlyavailabletocommunicatedelegatedprefixesto
aDHCPserverthatservessuchafunction.Thismaybeanitemof
futurework,shouldusagewarrant.
Troan&DromsStandardsTrack[Page2]
RFC3633IPv6PrefixOptionsforDHCPv6December2003
2.DHCPv6specificationdependency
ThisdocumentdescribesnewDHCPv6optionsforIPv6prefix
delegation.Thisdocumentshouldbereadinconjunctionwiththe
DHCPv6specification,RFC3315[2],foracompletespecificationof
thePrefixDelegationoptionsandmechanism.Definitionsforterms
andacronymsnotspecificallydefinedinthisdocumentaredefinedin
RFC3315.
3.Terminology
ThisdocumentusestheterminologydefinedinRFC2460[1]andRFC
3315.Inaddition,thisdocumentusesthefollowingterms:
requestingrouter:
TherouterthatactsasaDHCPclientandis
requestingprefix(es)tobeassigned.
delegatingrouter:
TherouterthatactsasaDHCPserver,andis
respondingtotheprefixrequest.
IdentityAssociationforPrefixDelegation(IA_PD):
Acollectionof
prefixesassignedtotherequestingrouter.Each
IA_PDhasanassociatedIAID.Arequesting
routermayhavemorethanoneIA_PDassignedto
it;forexample,oneforeachofitsinterfaces.
4.Requirements
ThekeywordsMUST,MUSTNOT,REQUIRED,SHALL,SHALLNOT,SHOULD,
SHOULDNOT,RECOMMENDED,MAY,andOPTIONAL,whentheyappearinthis
document,aretobeinterpretedasdescribedinBCP14,RFC2119[3].
5.ModelandApplicability
Themodelofoperationforprefixdelegationisasfollows.A
delegatingrouterisprovidedIPv6prefixestobedelegatedto
requestingrouters.Examplesofwaysinwhichthedelegatingrouter
maybeprovidedtheseprefixesaregiveninSection12.2.A
requestingrouterrequestsprefix(es)fromthedelegatingrouter,as
describedinSection12.1.Thedelegatingrouterchoosesprefix(es)
fordelegation,andrespondswithprefix(es)totherequesting
router.Therequestingrouteristhenresponsibleforthedelegated
prefix(es).Forexample,therequestingroutermightassignasubnet
fromadelegatedprefixtooneofitsinterfaces,andbeginsending
routeradvertisementsfortheprefixonthatlink.
Troan&DromsStandardsTrack[Page3]
RFC3633IPv6PrefixOptionsforDHCPv6December2003
Eachprefixhasanassociatedvalidandpreferredlifetime,which
constitutesanagreementaboutthelengthoftimeoverwhichthe
requestingrouterisallowedtousetheprefix.Arequestingrouter
canrequestanextensionofthelifetimesonadelegatedprefixand
isrequiredtoterminatetheuseofadelegatedprefixifthevalid
lifetimeoftheprefixexpires.
Thisprefixdelegationmechanismwouldbeappropriateforusebyan
ISPtodelegateaprefixtoasubscriber,wherethedelegatedprefix
wouldpossiblybesubnettedandassignedtothelinkswithinthe
subscriber'snetwork.
5.1.Examplenetworkarchitecture
Figure1illustratesanetworkarchitectureinwhichprefix
delegationcouldbeused.
______________________\
/\\
|ISPcorenetwork|\
\_____________________/|
||
+-------+-------+|
|Aggregation||ISP
|device||network
|(delegating||
|router)||
+-------+-------+|
|/
|DSLtosubscriber/
|premises/
|
+------+------+\
|CPE|\
|(requesting|\
|router)||
+----+---+----+|
|||Subscriber
---+-------------+-----+--+-----+-------------+---|network
|||||
+----+-----++-----+----++----+-----++-----+----+|
|Subscriber||Subscriber||Subscriber||Subscriber|/
|PC||PC||PC||PC|/
+----------++----------++----------++----------+/
Figure1:
Anexampleofprefixdelegation.
Troan&DromsStandardsTrack[Page4]
RFC3633IPv6PrefixOptionsforDHCPv6December2003
Inthisexample,thedelegatingrouterisconfiguredwithasetof
prefixestobeusedforassignmenttocustomersatthetimeofeach
customer'sfirstconnectiontotheISPservice.Theprefix
delegationprocessbeginswhentherequestingrouterrequests
configurationinformationthroughDHCP.TheDHCPmessagesfromthe
requestingrouterarereceivedbythedelegatingrouterinthe
aggregationdevice.Whenthedelegatingrouterreceivestherequest,
itselectsanavailableprefixorprefixesfordelegationtothe
requestingrouter.Thedelegatingrouterthenreturnstheprefixor
prefixestotherequestingrouter.
Therequestingroutersubnetsthedelegatedprefixandassignsthe
longerprefixestolinksinthesubscriber'snetwork.Inatypical
scenariobasedonthenetworkshowninFigure1,therequesting
routersubnetsasingledelegated/48prefixinto/64prefixesand
assignsone/64prefixtoeachofthelinksinthesubscriber
network.
Theprefixdelegationoptionscanbeusedinconjunctionwithother
DHCPoptionscarryingotherconfigurationinformationtothe
requestingrouter.Therequestingroutermay,inturn,thenprovide
DHCPservicetohostsattachedtotheinternalnetwork.Forexample,
therequestingrouterm
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