JNCIS的ISIS读书笔记.docx

JNCIS的ISIS读书笔记.docx

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JNCIS的ISIS读书笔记

第一部分ISIS的PDU包头结构1

1.IS-IScommonPDUheader1

2.IS-ISLANHelloPDU2

3.IS-ISPoint-to-PointHelloPDU3

4.CompleteSequenceNumberPDU4

5.PartialSequenceNumberPDU5

6.Link-StatePDU6

第二部分配置选项7

1.InterfaceCircuitID7

2.Authentication7

3.InterfaceMetrics7

4.MeshGroups8

第三部分TLV类型10

1.AreaAddressTLV10

2.ISReachabilityTLV10

3.ISNeighborsTLV11

4.PaddingTLV12

5.LSPEntryTLV13

6.AuthenticationTLV13

7.ChecksumTLV14

8.ExtendedISReachabilityTLV14

9.IPInternalReachabilityTLV15

10.ProtocolsSupportedTLV17

11.IPExternalReachabilityTLV17

12.IPInterfaceAddressTLV18

13.TrafficEngineeringIPRouterIDTLV18

14.ExtendedIPReachabilityTLV19

15.DynamicHostNameTLV20

16.GracefulRestartTLV20

17.Point-to-PointAdjacencyStateTLV21

第一部分ISIS的PDU包头结构

1.IS-IScommonPDUheader

ProtocolID（1octet）

Thisfieldissettoaconstantvalueof0x83anddesignatesthatthehigher-leveldatabelongstoIS-IS.

HeaderLength（1octet）

Thisfieldindicatesthetotallength,inoctets,oftheIS-ISheaders.ItincludesboththecommonIS-ISheaderandanyPDU-specificheadersthatfollow.

Version/ProtocolIDExtension（1octet）

Thisfieldissettoaconstantvalueof0x01.TheIS-ISspecificationdefinesthisfieldasanextensionareafortheProtocolIDdata.TheJUNOSsoftwaredoesnotimplementthisfunction.

IDLength（1octet）ThisfieldisusedtoinformothersystemsofthesystemIDlength.Forbackwardcompatibility,thedefaultlengthof6bytesisrepresentedwiththeconstantvalueof0x00.TheJUNOSsoftwaredoesnotusealargerIDsize,sothisfieldissettoaconstantvalueof0x00.

PDUType（1octet）ThisfielddesignatesthePDUcarriedafterthecommonheader.Thefirst3bitsaresetto0.Theremainingbitcombinationsinclude:

_Level1LANHello（15）

_Level2LANHello（16）

_Point-to-PointHello（17）

_Level1link-statePDU（18）

_Level2link-statePDU（20）

_Level1CompleteSNP（24）

_Level2CompleteSNP（25）

_Level1PartialSNP（26）

_Level2PartialSNP（27）

Version（1octet）Thisfieldissettoaconstantvalueof0x01,thecurrentIS-ISversion.

Reserved（1octet）Thisfieldissettoaconstantvalueof0x00andisignoredonreceipt.

MaximumAreaAddresses（1octet）Thisfieldissettoaconstantvalueof0x00.Itinformsothersystemshowmanyareaaddressesaresupportedbythelocalrouter.Avalueof0meansthatnomorethanthreeareaaddressesareassignedtothisrouter.

2.IS-ISLANHelloPDU

We’vepreviouslystatedthatIS-ISroutersexchangeIS-ISHello（IIH）PDUstoestablishanadjacency.WhilethepurposeoftheHelloPDUisthesame,therearethreedifferentformatstheroutercanuse.Oneisforpoint-to-pointlinks,andthetwoothersareforbroadcastlinks—oneeachforLevel1andLevel2.Recallfromthe“IS-ISLevels”sectionearlierthatL1routersmustsharethesameareaaddresstoformanadjacency,whileL2routersdonothavethislimitation.TheseparateLANHelloPDUssimplytellthereceivingroutertocheckorignorethisinformation.

L1LANHelloPDUsaremulticasttothe“AllL1ISs”addressof01:

80:

c2:

00:

00:

14.L2routerssharea

separatemulticastaddress“AllL2ISs2:

”00:

00:

of1:

80:

c5.BothLANHelloPDUsshareacommonpacketformat,asshowninFigure7.8.

TheIS-ISLANHelloPDUconsistsofthefollowingfields:

CircuitType（1octet）Thefirst6bitsaresetto0.Theremainingbitsdesignatethelevelatwhichtheinterfaceisoperating:

L1（0x01）,L2（0x02）,orL1/L2（0x03）.PDUswithavalueof0x00inthisfieldareignored.

SourceID（6octets）ThisfielddesignatesthesenderoftheIIH.Thefieldissettothe6-bytesystemIDofthesendingrouter.

HoldingTime（2octets）ThevalueinthisfieldrepresentstheamountoftimeeachneighboringroutershouldwaitbeforeterminatingtheadjacencyafterthelastreceivedIS-ISHelloPDUfromthisneighbor.

PDULength（2octets）ThevalueinthisfieldrepresentsthetotallengthoftheIS-ISHelloPDU.Thefieldissettoaconstantvalueof1492bytes（0x05D4）.

Priority（1octet）Thefirstbitissetto0.TheremainderofthebytedesignatesthevalueusedfortheelectionoftheDIS.ThedefaultvaluefortheJUNOSsoftwareis64.

LANID（7octets）ThisfielddesignatestheIDofthecurrentDISonthebroadcastcircuit.Thefieldissettothe6-bytesystemIDand1-bytecircuitIDoftheDIS.

TLVs（Variable）Thisfieldcontainsinformationaboutthesendingrouter,includingtheareaaddress,neighborID,authentication,andinterfaceaddressing.

3.IS-ISPoint-to-PointHelloPDU

IS-ISadjacenciesonpoint-to-pointlinksarealsoformedthroughtheadvertisementofHelloPDUs.On

broadcastlinks,separatePDUshavebeendefinedforLevel1andLevel2.OnlyasingleHelloPDUisdefinedforpoint-to-pointlinks.ThedesiretobeadjacentwithaneighboratL1,L2,orL1/L2isencodedintheCircuitTypefieldwithinthePDUitself.

CircuitType（1octet）Thefirst6bitsaresetto0.Theremainingbitsdesignatethelevelatwhichtheinterfaceisoperating:

L1（0x01）,L2（0x02）,orL1/L2（0x03）.PDUswithavalueof0x00inthisfieldareignored.

SourceID（6octets）ThisfielddesignatesthesenderoftheIIH.Itissettothe6-bytesystemIDofthesendingrouter.

HoldingTime（2octets）ThevalueinthisfieldrepresentstheamountoftimeeachneighboringroutershouldwaitbeforeterminatingtheadjacencyafterthelastreceivedIS-ISHelloPDU.

PDULength（2octets）ThetotallengthoftheIS-ISHelloPDUisencodedinthisfield.Thefieldissettoaconstantvalueof1492bytes（0x05D4）.

CircuitID（1octet）ThisfielddesignatesthespecificIDofthelocalrouterinterfacesshareavalueof0x01withintheJUNOSsoftware.

Allpoint-’tos-pointinterface.

TLVs（Variable）Thisfieldcontainsinformationaboutthesendingrouter,includingtheareaaddress,authentication,andinterfaceaddressing.

4.CompleteSequenceNumberPDU

TheCompleteSequenceNumberPDU（CSNP）containsacompletelistingofthelink-statePDUsinthelink-statedatabaseofthelocalrouter.TheCSNPprovidesanidentifier,alifetime,asequencenumber,andachecksumforeachpieceofinformationinthedatabase.ACSNPissentperiodicallyonbothbroadcastandpoint-to-pointlinkstomaintaindatabasecorrectness.Inaddition,CSNPsareadvertisedbetweentwoneighborsduringtheformationofanadjacency.

AswiththeIS-ISLANHelloPDUs,thereareseparateCSNPsforLevel1andLevel2usedonallmediatypes.

Level1PDUsaremulticasttothe“AllL1ISs”addressof01:

80:

c2:

00:

00:

14.Level2PDUsaremulticasttothe

“AllL2ISs”addressof01:

80:

c2:

00:

00:

15.Figure7.11showstheformatoftheCSNP.ThefieldsoftheCSNPinclude:

Length（2octets）ThetotallengthoftheCSNP,inoctets,isencodedinthisfield.

SourceID（7octets）ThisfielddesignatesthesenderoftheCSNP.Itissettothe6-bytesystemIDand1-bytecircuitID（0x00）ofthesendingrouter.

StartLSPID（8octets）Thisfieldissettoaconstantvalueof0x0000.0000.0000.00-00.ItdesignatesthesmallestpossibleLSPIDvalue.

EndLSPID（8octets）Thisfieldissettoaconstantvalueof0xFFFF.FFFF.FFFF.FF-FF.ItdesignatesthelargestpossibleLSPIDvalue.

TLVs（Variable）Thisfieldcontainsthesummarydatabaseinformationfromthelocalrouter.

5.PartialSequenceNumberPDU

AnIS-ISrouterusesthePartialSequenceNumberPDU（PSNP）torequestLSPinformationfromaneighbor.ThePSNPisalsousedtoexplicitlyacknowledgethereceiptofareceivedLSPonapoint-to-pointlink.Onabroadcastlink,CSNPsareusedasimplicitacknowledgments.

ThePSNPhasbothaLevel1andLevel2variety,liketheCSNPandIIHPDUs.Onbroadcastnetworks,Level

1PSNPsaremulticasttothe“AllL1ISs”addressof01:

80:

c2:

00:

00:

14andLevel2PSNPsaremulticasttothe“AllL2ISs”addressof01:

80:

c2:

00:

00:

15.TheformatofthePSNPisshowninFigure7.12.

APartialSequenceNumberPDUincludesthefollowingfields:

Length（2octets）ThetotallengthofthePSNP,inoctets,isencodedinthisfield.

SourceID（7octets）ThisfielddesignatesthesenderofthePSNP.Itissettothe6-bytesystemIDand1-bytecircuitID（0x00）ofthesendingrouter.

TLVs（Variable）ThisfieldcontainstherequesteddatabaseinformationortheLSPbeingacknowledged.

6.Link-StatePDU

Thusfar,we’vebeentalkingaboutthe-statelinkdatabasefromnumerousperspectives.IS-ISroutershaveformedadjacenciesandcomparedtheirdatabases.CompleteandPartialSequenceNumberPDUshave

beensentbetweenrouterstosynchronizethedatabases.We’vefailedtodiscusstheactualdatabase

informationtothispoint.Let’snowtacklethissubject.

Alink-statePDU（LSP）containsinformationabouteachrouterinthenetworkanditsconnectedinterfaces.MetricandIS-ISneighborinformationisalsoincluded.Figure7.13showstheformatofthelink-statePDU.Alink-statePDUincludesthefollowingfields:

Length（2octets）ThetotallengthoftheLSPisencodedinthisfield.

RemainingLifetime（2octets）Thisfieldliststheamountoftime,inseconds,eachroutershouldconsidertheLSPactive.TheJUNOSsoftwaredefaultlifetimevalueis1200seconds.

LSPID（8octets）ThisfielduniquelyidentifiestheLSPthroughoutthenetwork.ThevalueisacombinationofthesystemID（6bytes）,circuitID（1byte）,andLSPNumbervalue.

SequenceNumber（4octets）ThisfieldissettothecurrentversionnumberoftheLSP.Theinitialnumberis0x01andisincrementedeachtimetheoriginatingrouterupdatestheLSP.

Checksum（2octets）ThisfieldcontainsthechecksumvalueofthePDUfieldsaftertheRemainingLifetime.Attributes（1octet）Thisfieldcontainsmultiplesettingsrela