Fast ReRoute RFC 4090.docx

Fast ReRoute RFC 4090.docx

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FastReRouteRFC4090

NetworkWorkingGroupP.Pan,Ed.

RequestforComments:

4090HammerheadSystems

Category:

StandardsTrackG.Swallow,Ed.

CiscoSystems

A.Atlas,Ed.

AviciSystems

May2005

FastRerouteExtensionstoRSVP-TEforLSPTunnels

StatusofThisMemo

ThisdocumentspecifiesanInternetstandardstrackprotocolforthe

Internetcommunity,andrequestsdiscussionandsuggestionsfor

improvements.Pleaserefertothecurrenteditionofthe"Internet

OfficialProtocolStandards"（STD1）forthestandardizationstate

andstatusofthisprotocol.Distributionofthismemoisunlimited.

CopyrightNotice

Copyright（C）TheInternetSociety（2005）.

Abstract

ThisdocumentdefinesRSVP-TEextensionstoestablishbackuplabel-

switchedpath（LSP）tunnelsforlocalrepairofLSPtunnels.These

mechanismsenablethere-directionoftrafficontobackupLSPtunnels

in10sofmilliseconds,intheeventofafailure.

Twomethodsaredefinedhere.Theone-to-onebackupmethodcreates

detourLSPsforeachprotectedLSPateachpotentialpointoflocal

repair.Thefacilitybackupmethodcreatesabypasstunnelto

protectapotentialfailurepoint;bytakingadvantageofMPLSlabel

stacking,thisbypasstunnelcanprotectasetofLSPsthathave

similarbackupconstraints.Bothmethodscanbeusedtoprotect

linksandnodesduringnetworkfailure.Thedescribedbehaviorand

extensionstoRSVPallownodestoimplementeithermethodorbothand

tointeroperateinamixednetwork.

Pan,etal.StandardsTrack[Page1]

RFC4090RSVP-TEFastRerouteMay2005

TableofContents

1.Introduction...................................................3

1.1.Background...............................................4

2.Terminology....................................................4

3.LocalRepairTechniques........................................6

3.1.One-to-OneBackup........................................6

3.2.FacilityBackup..........................................7

4.RSVPExtensions................................................8

4.1.FAST_REROUTEObject......................................8

4.2.DETOURObject...........................................11

4.2.1.DETOURObjectforIPv4Address...................11

4.2.2.DETOURObjectforIPv6Address...................12

4.3.SESSION_ATTRIBUTEFlags.................................13

4.4.RROIPv4/IPv6Sub-objectFlags..........................14

5.Head-EndBehavior.............................................15

6.PointofLocalRepair（PLR）Behavior..........................16

6.1.SignalingaBackupPath.................................17

6.1.1.BackupPathIdentification:

Sender

Template-Specific................................19

6.1.2.BackupPathIdentification:

Path-Specific........19

6.2.ProceduresforBackupPathComputation..................20

6.3.SignalingBackupsforOne-to-OneProtection.............21

6.3.1.Make-before-BreakwithDetourLSPs...............22

6.3.2.MessageHandling.................................23

6.3.3.LocalRerouteofTrafficontoDetourLSP.........23

6.4.SignalingforFacilityProtection.......................24

6.4.1.DiscoveringDownstreamLabels....................24

6.4.2.ProceduresforthePLRbeforeLocalRepair.......24

6.4.3.ProceduresforthePLRduringLocalRepair.......25

6.4.4.ProcessingBackupTunnel'sERO...................26

6.5.PLRProceduresduringLocalRepair......................26

6.5.1.NotificationofLocalRepair.....................26

6.5.2.RevertiveBehavior...............................27

7.MergeNodeBehavior...........................................28

7.1.HandlingBackupPathMessagesbeforeFailure............28

7.1.1.MergingBackupPathsusingtheSender

Template-SpecificMethod.........................29

7.1.2.MergingDetoursusingthePath-SpecificMethod...29

7.1.3.MessageHandlingforMergedDetours..............31

7.2.HandlingFailures.......................................31

8.BehaviorofAllLSRs..........................................32

8.1.MergingDetoursinthePath-SpecificMethod.............32

9.SecurityConsiderations.......................................33

10.IANAConsiderations...........................................33

11.Contributors..................................................35

12.Acknowledgments...............................................36

13.NormativeReferences..........................................36

Pan,etal.StandardsTrack[Page2]

RFC4090RSVP-TEFastRerouteMay2005

1.Introduction

ThisdocumentextendsRSVP[RSVP]toestablishbackuplabel-switched

path（LSP）tunnelsforthelocalrepairofLSPtunnels.This

extensionwillmeettheneedsofreal-timeapplicationssuchasvoice

overIP,forwhichusertrafficshouldberedirectedontobackupLSP

tunnelsin10sofmilliseconds.Thistimingrequirementcanbe

satisfiedbycomputingandsignalingbackupLSPtunnelsinadvanceof

failureandbyre-directingtrafficasclosetothefailurepointas

possible.Inthisway,thetimeforredirectionincludesnopath

computationandnosignalingdelays,includingdelaystopropagate

failurenotificationbetweenlabel-switchedrouters（LSRs）.Speedof

repairistheprimaryadvantageofthemethodsandextensions

describedhere.Thetermlocalrepairisusedwhenreferringto

techniquesthatre-directtraffictoabackupLSPtunnelinresponse

toalocalfailure.

AprotectedLSPisanexplicitly-routedLSPthatisprovidedwith

protection.Therepairmethodsdescribedhereareapplicableonlyto

explicitly-routedLSPs.ApplicationofthesemethodstoLSPsthat

dynamicallychangetheirroutes,suchasLSPsusedinunicastIGP

routing,isbeyondthescopeofthisdocument.

Section2coversnewterminologyusedinthisdocument.Section3

describestwobasicmethodsforcreatingbackupLSPs.Section4

describestheRSVPprotocolextensionstosupportlocalprotection.

Section5presentsthebehaviorofanLSRthatseekstorequestlocal

protectionforanLSP.Thebehaviorofapotentialpointoflocal

repair（PLR）isgiveninSection6,whichdescribeshowtodetermine

theappropriatestrategyforprotectinganLSPandhowtoimplement

eachofthestrategies.Section7describesthebehaviorofamerge

node,theLSRwhereaprotectedLSPanditsbackupLSPrejoin.

Finally,Section8discussestherequiredbehaviorofothernodesin

thenetwork.

Themethodsdiscussedinthisdocumentdependuponthreeassumptions:

oAnLSRthatisonthepathofaprotectedLSPshouldalways

assumethatitisamergepoint.Thisisnecessarybecause

thefacilitybackupmethoddoesnotsignalbackupsthrougha

bypasstunnelbeforefailure.

oIftheone-to-onebackupmethodisusedandaDETOURobject

isincluded,theLSRsinthetraffic-engineerednetwork

shouldsupporttheDETOURobject.Thisisnecessarysothat

thePathmessagecontainingtheDETOURobjectisnot

rejected.

Pan,etal.StandardsTrack[Page3]

RFC4090RSVP-TEFastRerouteMay2005

oUnderstandingtheDETOURobjectisrequiredtosupportthe

path-specificmethod,whichrequiresthatLSRsinthe

traffic-engineerednetworkbecapableofmergingdetours.

1.1.Background

Severalyearsbeforeworkbeganonthisdocument,operational

networkshaddeployedtwoindependentmethodsofdoingfastreroute;

thesemethodsarecalledhereone-to-onebackupandfacilitybackup.

Vendorstryingtosupportbothmethodsexperiencedcompatibility

problemsinattemptingtoproduceasingleimplementationcapableof

interoperatingwithbothmethods.Therearetechnicaltradeoffs

betweenthemethods.Thesetradeoffsaresotopologicallydependent

thatthecommunityhasnotconvergedonasingleapproach.

ThisdocumentrationalizestheRSVPsignalingforbothmethodsso

thatanyimplementationcanrecognizeallfastrerouterequestsand

clearlyrespond.Theresponsemaybepositiveifthemethodcanbe

performed,oritmaybeaclearerrortoinformtherequestertoseek

alternatebackupmeans.Thisdocumentalsoallowsasingle

implementationtosupportbothmethods,therebyprovidingarangeof

capabilities.ThedescribedbehaviorandextensionstoRSVPallow

LERsandLSRstoimplementeithermethodorboth.

Whilethetwomethodscouldinprinciplebeusedinasinglenetwork,

itisexpectedthatoperatorswillcontinuetodeployeitheroneor

theother.ThegoalofthisdocumentistostandardizetheRSVP

signalingsothatanetworkcomposedofLSRsthatimplementboth

methodsoranetworkcomposedofsomeLSRsthatsupportonemethod

andothersthatsupportbothcanproperlysignalamongthoseLSRsto

achievefastrestoration.

2.Terminology

Thekeywords"MUST","MUSTNOT","REQUIRED","SHALL","SHALLNOT",

"SHOULD","SHOULDNOT","RECOMMENDED","MAY",and"OPTIONAL"inthis

documentaretobeinterpretedasdescribedinRFC2119[RFC-WORDS].

Thereaderisassumedtobefamiliarwiththeterminologyin[RSVP]

and[RSVP-TE].

LSR:

Label-SwitchRouter.

LSP:

AnMPLSLabel-SwitchedPath.Inthisdocument,anLSPwill

alwaysbeexplicitlyrouted.

LocalRepair:

TechniquesusedtorepairLSPtunnelsquicklywhena

nodeorlinkalongtheLSP'spathfails.

Pan,etal.StandardsTrack[Page4]

RFC4090RSVP-TEFastRerouteMay2005

PLR:

PointofLocalRepair.Thehead-endLSRofabackuptunnel

oradetourLSP.

One-to-OneBackup:

AlocalrepairmethodinwhichabackupLSPis

separatelycreatedforeachprotectedLSPataPLR.

FacilityBackup:

Alocalrepairmethodinwhichabypasstunnelis

usedtoprotectoneormoreprotectedLSPst