RFC3633.docx

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

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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.

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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.

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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.

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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