3 introduction to isis 6up

8/12/2019 3 Introduction to ISIS 6up

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1Page 1

11999,CiscoSystems,Inc.

Introduction to ISISIntroduction to ISISIntroduction to ISIS

ISP/IXP WorkshopsISP/IXP WorkshopsISP/IXP Workshops

2ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com

AcknowledgementsAcknowledgementsAcknowledgements

Thanks to Stefano Previdi

Any questions


Basic ISISBasic ISISBasic ISIS



ISIS - Intermediate System toISIS - Intermediate System toIntermediate SystemIntermediate System

Link state protocol for IP and CLNS,RFC1195, ISO 10589

Each router sends Hello PDU IIHs andbuild adjacencies with neighbours

Each router creates an LSP and floodit to neighbours

Each router receives all LSPs fromneighbours


Introduction to ISISIntroduction to ISIS

Each router maintains database (L1, L2, orboth)

Each router runs the Dijkstra (SPF)algorithm on the database to calculatetopology

Each router runs Partial Route Calculation

(PRC) to calculate IP routing information

Each router has the full visibility of thenetwork (or the area)


ISIS LevelsISIS Levels

ISIS has a 2 layer hierarchy

Level-2 (the backbone)

Level-1 (the areas)

A router can be

Level-1 (L1) routerLevel-2 (L2) router

Level-1-2 (L1L2) router


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Level-1 routerHas neighbours only on the same area

Has a level-1 LSDB with all routing information for thearea

Level-2 router

Mayhave neighbours in the same or other areas

Has a Level-2 LSDB with all routing information aboutinter-area

Level-1-2 router

May have neighbours on any area.

Has two separate LSDBs: level-1 LSDB & level-2 LSDB


BackboneBackbone

ISIS does not have a backbone

area

The backbone is the contiguous

collection of Level-2 capable

routers


L1L2

L1L2

L1L2

L1L2

L1L2

L1-only

L2-only

L1-only

L1, L2, and L1L2 Routers

Area-2

Area-1

Area-3

Area-4

L1-only

L1-only


ISIS AreasISIS Areas

ISIS area borders are on links, not

routers

Each router is identified with

Network Entity Title (NET)

NET: An NSAP where n-selector is 0


NSAP and AddressingNSAP and Addressing

NSAP: Network Service Access Point

Total length between 8 and 20 bytes

Area Address: variable length field (up to 13 bytes)

System ID: defines an ES or IS in an area.

NSEL: N-selector. identifies a network service user(transport entity or the IS network entity itself)

NET: the address of the network entity itself12ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com

An Addressing ExampleAn Addressing Example

39.0f01.0002.3333.3333.3333.00

39.0f01.0001.2222.2222.2222.00

39.0f01.0001.1111.1111.1111.00

39.0f01.0004.7777.7777.7777.00

39.0f01.0003.6666.6666.6666.00

39.0f01.0004.8888.8888.8888.00

39.0f01.0002.4444.4444.4444.00

Area 1

Area 3

Area 4

Area 2


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Hello PDU IIHs are exchangedbetween routers to formadjacencies

Area addresses are exchanged inIIH PDUs

AdjacenciesAdjacencies

ISIS adjacency through IIH


Link State PDU (LSP)Link State PDU (LSP)

Each router creates an LSP and flood it

to neighbors

A level-1 router will create level-1 LSP(s)

A level-2 router will create level-2 LSP(s)

A level-1-2 router will create

level-1 LSP(s) and

level-2 LSP(s)


LSP headerLSP header

LSPs have

Fixed header

TLV coded contents

The LSP header contains

LSP-id

Sequence number

Remaining Lifetime

Checksum

Type of LSP (level-1, level-2)

Attached bit

Overload bit


LSP ContentsLSP Contents

The LSP contents are coded asTLV (Type, Length, Value)

Area addresses

IS neighbors

Authentication Info


LSDB contentLSDB content

Each router maintains a separate LSDB for

level-1 and level-2 LSPs

LSP headers and contents

SRM bits: set per interface when router has

to flood this LSP

SSN bits: set per interface when router has

to send a PSNP for this LSP


Flooding of LSPsFlooding of LSPs

New LSPs are flooded to all neighbors

It is necessary that all routers get all

LSPs

Each LSP has a sequence number

2 kinds of flooding

Flooding on a p2p link

Flooding on LAN


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Complete Sequence NumberComplete Sequence NumberPDUPDU

Describes all LSPs in your LSDB (inrange)

If LSDB is large, multiple CSNPs aresent

Used at 2 occasions

Periodic multicast by DIS (every 10seconds) to synchronise LSDB overLAN subnets

On p2p links when link comes up


Partial Sequence NumberPartial Sequence Number PDUsPDUs

PSNPs Exchanged on p2p links (ACKs)

Two functions

Acknowledge receipt of an LSP

Request transmission of latest LSP

PSNPs describe LSPs by its header

LSP identifier

Sequence number

Remaining lifetime

LSP checksum


ConfigurationConfiguration

L1, L2, L1-L2

By default cisco routers will be L1L2 routers

Routers can be manually configured tobehave as

Level-1 only, Level-2 only, Level-1-2

Configuration can be done perinterface or at the router level

Area-2 Area-3Area-1

Rtr-A Rtr-BRtr-C



Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Router-B

Interface Loopback0

ip address 192.168.1.1 255.255.255.255

!

Interface Pos2/0/0

ip address 192.168.222.1 255.255.255.0

ip router isis

isis circuit-type level-2

!

FastEthernet4/0/0ip address 192.168.120.10 255.255.255.0

ip router isis


!

router isis

passive-interface Loopback0

net 49.0001.1921.6800.1001 .00

Router-A

Interface Loopback0

ip address 192.168.1.5 255.255.255.255

!interface FastEthernet0/0

ip address 192.168.120.5 255.255.255.0

ip router isis

!

router isis

is-type level-1


net 49.0001.1921.6800.1005 .00 29ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com


Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Router-C

Interface Loopback0

ip address 192.168.2.2 255.255.255.255

!

Interface Pos1/0/0

ip address 192.168.222.2 255.255.255.0

ip router isis


!

interface Fddi3/0

ip address 192.168.111.2 255.255.255.0

ip router isis


!

router isis


net 49.0002.1921.6800.2002 .00

Router-D

Interface Loopback0

ip address 192.168.2.4 255.255.255.255

!

interface Fddi6/0

ip address 192.168.111.4 255.255.255.0

ip router isis

!

router isis

is-type level-1


net 49.0002.1921.6800.2004 .00 30ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com

Show CLNSShow CLNS

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> sh clnsGlobal CLNS Information:

2 Interfac es Enabled for CLNS NET: 49.0001.1921.6800.1001.00

Con figuration Timer: 60, Default Holding Timer: 300, Packet

Lifetime 64 ERPDU's requested on locally generated packets

Int ermediate system operation enabled (forwarding allowed) IS-IS level-1-2 Router:

Routing for Area: 49.0001


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ShowShow clnsclns neighborsneighbors

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> show clns neighbors

System Id SNPA Interface State Holdtime Type Protocol

1921.6800.2002 *PPP* PO2/0/0 Up 29 L2 IS-IS1921.6800.1005 00e0.1492.2c00 Fa4/0/0 Up 9 L1 IS-IS


ShowShow clnsclns interfaceinterface

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> s h clns int POS2/0/0POS2/0/0 is up, line protocol is up

Checksums enabled , MTU 4470, Encapsulation PPP

ERPDUs enabled, min. interval 10msec.

RDPDUs enabled, min. interval 100 msec.,AddrMask enabled

Congestion Experienced bit set at 4 packets

CLNS fast switching disabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Nex t ESH/ISH in 47 seconds

Routing Protocol: IS-IS

Circuit Type: level-1-2

Interface number 0x0, local circuit ID 0x100

Level-1 Metric: 10, Priority: 64, Circuit ID: 1921.6800.2 002.00

Number of active level-1 adjacencies: 0

Level-2 Metric: 10, Priority: 64, Circuit ID: 1921.6800.1 001.00


Next IS-IS Hello in 2 seconds


ShowShowclnsclnsinterfaceinterface

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> sh clns int FastEthernet4/0/0

FastEthernet4/0/0 is up, line protocol is up

Checksums enabled, MTU 1497, Encapsulation SAP

ERPDUs enabled, min. interval 10msec.

RDPDUs enabled, min. interval 100 msec.,AddrMask enabled

Congestion Experienced bit set at 4 packets

CLNS fast switching enabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Next ESH/ISH in 1 seconds

Routing Protocol: IS-IS

Circuit Type: level-1

Interface number 0x1, local circuit ID 0x1

Level-1 Metric: 10, Priority: 64, Circuit ID: 1921.6800.1005.01


Next IS-IS LAN Level-1 Hello in 3 seconds


ShowShow clnsclns protocolprotocol

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> show cln sprotocol

IS-IS Router:

System Id: 1921.6800.1001.00 IS-Type: level-1-2

Manual area address(es):

49.0001

Routing for area address(es):

49.0001

Interfaces supported by IS-IS:

FastEthernet4/0/0 - IP

POS2/0/0 - IP

Redistributing:

static

Distance: 110

Rtr-B>


ShowShow clnsclns traffictraffic

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> show clnstraffic

CLNS & ESIS Output: 14, Input: 436

CLNS Local: 0, Forward: 0

CLNS Discards:

Hdr Syntax: 0, Checksum: 0, Lifetime: 0, Output cngstn:0

No Route: 0,Dst Unreachable 0,Encaps. Failed: 0

NLP Unknown: 0, Not an IS: 0

CLNS Options: Packets 0, total 0, bad 0, GQOS 0, cngstn exprncd 0

CLNS Segments: Segmented: 0, Failed: 0

CLNS Broadcasts: sent: 0, rcvd: 0

Echos: Rcvd 0 requests, 0 replies

Sent 0 requests, 0 replies

ESIS(sent/rcvd): ESHs: 0/0, ISHs: 14/15,RDs: 0/0, QCF: 0/0

ISO-IGRP: Querys (sent/rcvd): 0/0 Updates (sent/rcvd): 0/0

ISO-IGRP: Router Hellos: (sent/rcvd): 0/0

ISO-IGRP Syntax Errors: 0

IS-IS: Level-1 Hellos (sent/rcvd): 84/244

IS-IS: Level-2 Hellos (sent/rcvd): 0/0

IS-IS: PTP Hellos (sent/rcvd): 84/82


ShowShowclnsclnstraffictraffic

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

IS-IS: Level-1 LSPs sourced (new/refresh): 7/1

IS-IS: Level-2 LSPs sourced (new/refresh): 5/0

IS-IS: Level-1 LSPs flooded (sent/rcvd): 5/5

IS-IS: Level-2 LSPs flooded (sent/rcvd): 1/6

IS-IS: LSP Retransmissions: 0

IS-IS: Level-1 CSNPs (sent/rcvd): 0/82

IS-IS: Level-2 CSNPs (sent/rcvd): 1/1

IS-IS: Level-1 PSNPs (sent/rcvd): 1/0

IS-IS: Level-2 PSNPs (sent/rcvd): 3/1

IS-IS: Level-1 DR Elections: 2

IS-IS: Level-2 DR Elections: 1

IS-IS: Level-1 SPF Calculations: 3

IS-IS: Level-2 SPF Calculations: 3

IS-IS: Level-1 Partial Route Calculations: 0

IS-IS: Level-2 Partial Route Calculations: 0

IS-IS: LSP checksum errors received: 0IS-IS: Update process queue depth: 0/200

IS-IS: Update process packets dropped: 0


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ShowShow isisisis databasedatabase

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routersRtr-B> show isis database

IS-IS Level-1 Link State Database

LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL

1921.6800.1001.00-00* 0x00000019 0x2783 1153 1/0/0 (11)

1921.6800.1005.00-0 0 0x0000000C 0x2179 905 0/0/0 (5)

1921.6800.1005.01-00 0x00000009 0x40EC 831 0/0/0 (4)



1921.6800.1001.00-00* 0x00000010 0xFC45 1153 0/0/0 (9)

1921.6800.1001.01-00* 0x00000001 0x4CB7 1137 0/0/0 (10)

1921.6800.2002 .00-00 0x00000018 0x86A6 1141 0/0/0 (3)

1921.6800.2002.02-00 0x00000004 0x8558 881 0/0/0 (2)


ShowShowisisisisdatabasedatabase

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> sh isisdatab ase 1921.6800.1001.00-00 detail

IS-IS Level-1 LSP 1921.6800.1001.00-00


1921.6800.10 01.00-00* 0x00000006 0x4D70 991 1/0/0 (1)

Area Address: 49.0001

NLPID: 0xCC

IP Address: 192.168.120.10

Metric: 10 IP 192.168.222.0 255.255.255.0

Metric: 10 IP 192.168.120.0 255.255.255.0

Metric: 0 IP 192.168.1.1 255.255.255.255

Metric: 10 IS 1921.6800.1005.01

Metric: 0 ES 1921.6800.1001


ShowShowisisisisdatabasedatabase

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

IS-IS Level-2 LSP 1921.6800.1001.00-00


1921.6800.1001.00-00* 0x00000004 0x1539 980 0/0/0 (2)


NLPID: 0xCC

IP Address: 192.168.222.1

Metric: 10 IS 1921.6800.1001.01

Metric: 10 IS 1921.6800.2002.00

Metric: 10 IP 192.168.120.0 255.255.255.0

Metric: 0 IP 192.168.1.1 255.255.255.255

Metric: 10 IP 192.168.1.5 255.255.255.255

Metric: 10 IP 192.168.222.0 255.255.255.0


ShowShow isis spfisis spf-log-log

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routersRtr-B> show isis spf-log

Level 1 SPF log

When Duration Nodes Count Last trigger LSP Triggers00:06:30 0 1 6 1921.6800.1001.00-00 NEWAREA RTCLEARED NEWADJ NEWLSP

TLVCONTENT00:06:20 0 3 3 1921.6800.1005.01-00 NEWADJ TLVCONTENT00:06:05 0 3 2 1921.6800.1 001.00-00 ATTACHFLAG LSPHEADER

Level 2 SPF log When Duration Nodes Count Last trigger LSP Triggers00:06:31 0 1 2 1921.6800.100 1.00-00 RTCLEARED NEWLSP00:06:21 0 1 3 1921.6800 .1001.00-00 NEWADJ TLVCODE TLVCONTENT00:06:11 0 2 1 1921.6800.2002.00-00 LSPHEADER


Network Design IssuesNetwork Design Issues

As in all IP network designs, the key issueis the addressing lay-out

ISIS support large number of routers in a

single area

When using areas, use summary-addresses

400 routers in the backbone has been done


Network Design IssuesNetwork Design Issues

Possible link cost

Default on all interface is 10

Manually configured according to routing strategy

Summary address cost

Equal to the best more specific cost

Plus cost to reach neighbor of best specific

Backbone has to be contiguousEnsure continuity by redundancy

Area partitioning

Design so that backbone can not be partitioned


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Scaling IssuesScaling Issues

Areas vs. single areaUse areas where

sub-optimal routing is not an issue

areas with one single exit point

Start with L2-only everywhere is a goodchoice

Future implementation of level-1 areas will beeasier

Backbone continuity is ensured from start


Advanced ISISAdvanced ISISAdvanced ISIS

44ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com 45ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com


Level-1 router

Use the closest Level-2 router to exitthe area

Level-1-2 router

If the router has adjacencies to otherareas, it will inform the level-1 routers(intra-area) it is a potential exit pointfor the area


Non-Pseudonode LSPNon-Pseudonode LSP

Non-Pseudonode LSP represents router

Each router will create and flood a newNon-Pseudonode LSP

When a new neighbor comes up or goes away

When new IP prefixes are inserted or removed

When the metric of a link is changed

When refresh interval timer expires


Pseudonode LSPPseudonode LSP

Pseudonode LSP represents LAN

The DIS will create and flood anew Pseudonode LSP

When a new neighbour comes up orgoes away

When refresh interval timer expires Reduces adjacencies and flooding

over LAN subnets


LSP IdentifierLSP Identifier

LSP identifier consists of 3 parts

Source ID

System-ID of router (non-PN) or DIS (Pseudonode)

Pseudonode ID

Zero for router LSP, non-zero for Pseudonode LSP

LSP number

Fragmentation number

Example: 00c0.0040.1234.02-00

SystemID

PN-ID

Frag-Nr


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LSP HeaderLSP Header

LSP sequence numberUsed to determine the newest LSP

version

LSP remaining lifetime

Used to purge old LSPs

LSP checksum

LSP type

level-1 or level250ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com


LSP Attached bit

Set in the level-1 LSP by a L1-L2 routerif it has connectivity to another area

Indicate to the area routers (level-1)that it is a potential exit point of thearea

Level-1 routers select the closest (bestmetric) level-2 router with the ATT-bitset



LSP Overload bitSet by the router when it has an overload

problem on its LSDB

The O-bit Indicates that the router has anincomplete LSP database, and hence cannot betrusted to compute any correct routes

LSP with O-bit is used in the LSDB but topologybehind it is not calculated

Therefore other routers do not compute routeswhich would require the PDU to pass through

the overloaded router


Flooding in depthFlooding in depth

LSPs hold a Remaining LifetimeSet to 20 minutes by the originating router

After 20 min. each router must remove the LSP

Prevents old LSPs to stay in the LSDB forever

Periodic refresh of LSPs

router resends LSP at least every 15 mins

Can be set up to 18.7 Hours

Cut back on background LSP noise



Network wide LSP purges

When a router detects a corrupted or anexpired LSP, it sets RL to 0, and floods theLSP header

All routers will now remove the LSPsimultaneous

New DIS purges old Pseudonode LSP

LSPs hold a checksum

To detect LSDB corruption in routers memory



Sequence number overflow is unlikelyto happen

4 Bytes seqnr is enough for 120 years

Restarting of a router

Use sequence number = 1

Neighbour will flood old LSP with old

sequence numberRouter can now set sequence number higher

then before reboot, so everyone will usethe latest LSP


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LSP refreshLSP refresh

LSP are refreshed when refresh timerexpires

Refresh-timer trigger new LSP generation andflooding

LSP lifetime (LSP header) gives remaining time

LSP lifetime is used by routers anddecremented

When lifetime is 0, LSP purged from LSDB

Decrement allows different lifetimes per router


Configurable TimersConfigurable Timers

Timers are configurablecsnp-interval Set CSNP interval in seconds

hello-interval Set Hello interval in seconds

hello-multiplier Set multiplier for Hello holding time

lsp-interval Set LSP transmission interval

retransmit-interval Set per-LSP retransmission interval

retransmit-throttle- interval Set interface LSP retransmission interval

lsp-gen-interval Minimum interval between regenerating same LSP

lsp-refresh-interval Set LSP refresh interval

max-lsp-lifet ime Set maximum LSP lifetime

prc-interval Minimum interval between partial route calculations

spf-interval Minimum interval between SPF calculations


New FeaturesNew Features

Metrics are 3 bytes (2^24) wide with 12.0S

Specific routes leaking from L2 to L1 with

12.0S

Mesh-groups

Mesh-groups allow LSP flooding on selected sub-

interface (thus neighbours)

Avoid flooding over all interfaces

Use is recommended on NBMA clouds


Mesh-groupMesh-group

Router-B will receive 4 instances of Router-A LSP

Mesh-groups will allow to flood only on selected links

Mesh-groups are configured on interfaces

Router-B

Router-A


Timer IssuesTimer Issues

Timers can be adapted to large topologies

LSP, Hello, CSNP, retransmission intervals

Refresh interval

Trade-off between reduced flooding and purge of corrupted

LSPs

SPF and PRC interval

LSP maximum lifetime

Maximum value is recommended

Will significantly reduce LSP re-flooding

Old copies of LSPs may be present in LSDB (but will not be

used).60ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com

Timer IssuesTimer Issues

In some topological cases really fastconvergence is needed

HSRP and ISIS

With HSRP the routers have to convergerapidly in order to switch from/to active andpassive states

Hello-interval and lsp-gen-interval can bereduced

routing traffic will increase (possible routeflapping)


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IP SummarisationIP Summarisation

A L1L2 router will insert L1 IPprefixes into its L2 LSP

Summarisation reduces L2 LSDBsize

Configurable on Level-1 andLevel-2 routers

More specific should be present


IP SummarisationIP Summarisation

Summary addresses for level-1

summary address is created forredistributed prefixes

Summary addresses for level-2

summary address is created for

redistributed prefixes

L1 routes


IP specificIP specific

Default routingBoth level-1 and level-2 ISs can

generate a default route

A level-1 IS will always prefer a level-1default route BEFORE using the ATT(closest level-2 capable IS)

Creates an IP External prefix in L1 or L2non-PN LSP


Default routeDefault route

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-A> show ip route

Gateway of last resort is 192.168.120.10 to network 0.0.0.0C 192.168.120.0/24 is directly connected, FastEthernet0/0

192.168.1.0/32 is subnetted, 2 subnet s

i L1 192.168.1.1 [115/10] via 192.168.120.10, FastEthernet0/0

C 192.168.1.5 is directly connected, Loopback0

i L1 192.168.222.0/24 [115/20] via 192.168.120.10, FastEthernet0/0

i*L1 0.0.0.0/0 [115/10] via 192.168.120.10, FastEthernet0/0


Summary routeSummary route

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routersrouterisis

summary-address 55.0.0.0 255.0.0.0 level-1-2summary-address 192.168.1.0 255.255.255.0 level-1-2

redistribute static ip metric 44 level-1-2 passive-interface Loopback0

net 49.0001.1921.6800.1001.00!

ip route 55.1.0.0 255.255.0.0 Null0

ip route 55.2.0.0 255.255.0.0 Null0



Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B> sh isis da 1921.6800.1001.00-00 det

IS-IS Level-1 LSP 1921.6800.1001.00-00


1921.6800.1001.00-00* 0x00000062 0x770C 1028 1/0/0 (1)


NLPID: 0xCC

IP Address: 192.168.120.10

Metric: 10 IP 192.168.222.0 255.255.255.0

Metric: 10 IP 192.168.120.0 255.255.255.0

Metric: 0 IP 192.168.1.1 255.255.255.255

Metric: 10 IS 1921.6800.1005.01

Metric: 0 ES 1921.6800.1001Metric: 44 IP-External 171.68.0.0 255.255.0.0

Metric: 44 IP-External 172.17.0.0 255.255.0.0




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1Page 12



Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

IS-IS Level-2 LSP 1921.6800.1001.00-00


1921.6800.100 1.00-00* 0x0000005F 0xB264 1027 0/0/0 (2)


NLPID: 0xCC

IP Address: 192.168.222.1

Metric: 10 IS 1921.6800.1001.01

Metric: 10 IS 1921.6800.2002.00


Metric: 10 IP 192.168.120.0 255.255.255.0



Metric: 10 IP 192.168.222.0 255.255.255.0


Metric: 0 IP 192.168.1.0 255.255.255.0


Attached bitAttached bit

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-A> showisis database



1921.6800.10 01.00-00 0x00000006 0x4D70 666 1/0/0 (4)

1921.6800.1001.0 1-00 0x00000001 0x1136 0 (648) 0/0/0 (3)

1921.6800.1005.00-00* 0x00000002 0x356F 647 0/0/0 (1)

1921.6800.100 5.01-00* 0x00000001 0x50E4 647 0/0/0 (2)


DebugDebug isis adjisis adj-packets-packets

Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

Rtr-B# debug isis adj-packets

ISIS-Adj: Rec L1 IIH from 00e0.1492.2c00 (FastEthernet4/0/0),cirtype 1, cir id 1921.6800.1005.01 ISIS-Adj: Sending L1 IIH on FastEthernet4/0/0

ISIS-Adj: Rec L1 IIH from 00e0.1492.2c00 (FastEthernet4/0/0),cirtype 1, cir id 1921.6800.1005.01 ISIS-Adj: Sending serial IIH on POS2/0/0

ISIS-Adj: Rec serial IIH from *PPP* on POS2/0/0, cir type 3, cirid 00


Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

DebugDebug isis spfisis spf-events-events

Rtr-B#debug isis spf-events

ISIS-SPF: Compute L1 SPT

ISIS-SPF: Move 1921.6800.1001.00-00 to PATHS, metric 0

ISIS-SPF:thru2147483647/2147483647/2147483647, delay 0/0/0,mtu2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0

ISIS-SPF:Add 1921.6800.1005.01-00to TENT,metric 10

ISIS-SPF: Nexthop local


ISIS-SPF:thru2147483647/2147483647/2147483647, delay 0/0/0,mtu2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0

ISIS-SPF: considering adj to 1921.6800.1005 (FastEthernet4/0/0) metric 10

ISIS-SPF: (accepted)

ISIS-SPF:Add 1921.6800.1005.00-00to TENT,metric 10ISIS-SPF: Next hop 1921.6800.1005 (FastEthernet4/0/0)


ISIS-SPF: Add 192.168.120.0/255.255.255.0 to IP route table, metric 20

ISIS-SPF: Next hop 1921.6800.1005/192.168.120.5 (FastEthernet4/0/0) (rejected)


ISIS-SPF: Next hop 1921.6800.1005/192.168.120.5 (FastEthernet4/0/0) (accepted)


ISIS-SPF: Next hop 1921.6800.1005/192.168.120.5 (FastEthernet4/0/0) (rejected)71ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com

DebugDebug isis snpisis snp-packets-packets

Rtr-B# debug isis snp-packets

ISIS-SNP: Rec L1 CSNP from 1921.6800.1005 (FastEthe rnet4/0/0)

ISIS-SNP: CSNP range 0000.0000.0000.00-00 to FFFF.FFFF.FFFF.FF-FF

ISIS-SNP: Same entry 1921.6800.1001.00-00,seq93



Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers


Area 49.0001 Area 49.0002

Rtr-CRtr-B

Rtr-A Rtr-D

L1L2 routers

L1routers

DebugDebug isis spfisis spf-update-update

Rtr-B(config)#intfa4/0/0

Rtr-B(config -if)#isis metric 13Rtr-B(config-if)#^Z

Rtr-B#

ISIS-SPF-TRIG: L1, new metric

ISIS-Update: Building L1 LSP

ISIS-Update: TLV contents different, code 80ISIS-Update: TLV contents different, code 2

ISIS-SPF-TRIG: L1, 1921.6800.1001.00-00 TLV contents changed, code 2

ISIS-Update: Full SPF required

ISIS-Update: Sending L1 LSP 1921.6800.1001.00-00, seq 96, ht 1199 on FastEthernet4/0/0

ISIS-SNP: Rec L1 CSNP from 1921.6800.1005 (FastEthernet4/0/0)

ISIS-Stats: Compute L1 SPTISIS-Stats: Complete L1 SPT, Compute time 0.000, 3 nodes, 2 links on SPT, 0 suspends


ISIS-Update: TLV contents different, code 80


ISIS-Update: Leaf routes changedISIS-Update: Sending L2 LSP 1921.6800.1001.00-00, seq 96, ht 1199 on POS2/0/0


ISIS-Update: Rate limiting L2 LSP 1921.6800.1001.00-00,seq 97



ISIS-Update: Leaf routes changedISIS-Update: Sending L2 LSP 1921.6800.1001.00-00, seq 97, ht 1196 on POS2/0/0


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2 routers with the same System-ID2 routers with the same System-ID

This is an illegal configuration

Possible duplicate System-IDs warning

2 Routers with same System-ID will see eachothers LSP as their own, but not correct. Sothey will generate a new LSP with highersequence number.

This is an infinite ping-pong game

When an IS has to regenerate its LSP frequently,it will generate the above warning


id=x.00-00

seqnr=22

RL=1200

LSP Checksum ThrashingLSP Checksum Thrashing

id=x.00-00

seqnr=23

RL=1200

LSP ->id=x.00-00

seqnr=22

RL=1193

this IS got the LSP with

a checksum error.

So it purges it.

id=x.00-00

seqnr=23

RL=1194

someone purged

our LSP. lets

regenerate it

And on and on and ...

78

3 introduction to isis 6up

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