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© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1BSCI Module 4

Lesson 3

The IS-IS Protocol

BSCI Module 4

Introducing IS-IS and Integrated IS-IS Routing

2

What is IS-IS ?

� IS stands for Intermediate System

� IS is “OSI speak” for router

� IS-IS is the Intermediate System to Intermediate System intra-domain routing protocol

� IS-IS was defined in 1992 in the ISO/IEC recommendation 10589



3

OSI: Two Network Services, Two Network Protocols

� CMNS (Connection Mode Network Service) – Requires establishment of a path between transport layer entites.

CONP (Connection-Oriented Network Protocol) – OSI network layer protocol that carries upper layer data over connection-oriented links.

� CLNS (Connectionless Network Service) – Performs datagram support, does not require circuit to be established

CLNP (Connectionless Network Protocol) – OSI network layer protocol that carries upper layer data over connectionless links. (Similar to IP)

4

IS-IS Protocol Options

� IS-IS (ISO 10589)

Dynamic link state routing protocol used in an ISO CLNS environment.

� ISO-IGRP

Cisco IOS offers proprietary routing protocol for CLNS.

Based on IGRP, distance vector technology.

Can be used for Level 3 Routing, between IS-IS domains (next)

� Integrated IS-IS (RFC 1195)

IS-IS for mixed ISO CLNS and IP environments.

Either:

Purely ISO

Purely IP (CCNP 1)

Both



5

IS-IS versus OSPF

� OSPF – discussed in CCNA and CCNP (Single Area and Multi-Area)

� The following slides show terminology differences between IS-IS and OSPF.

� Similar to the differences between Spanish and Italian.

“IS-IS is exactly the same as OSPF only completely different”

6

Similarities Between IS-IS and OSPF

� Integrated IS-IS and OSPF are both open standard link-state protocols with the following similar features:

Link-state representation, aging timers, and LSDB synchronization

SPF algorithms

Update, decision, and flooding processes

VLSM support

� Scalability of link-state protocols has been proven (used in ISP backbones).

� They both converge quickly after changes.



7

Advantages of Integrated IS-IS

� Supports CLNP and IP

� More extensible through TLV design

8

Advantages of OSPF

� OSPF has more features, including:

Has three area types: normal, stub, and NSSA

Defaults to scaled metric (IS-IS always 10)

� OSPF is supported by many vendors.

� Information, examples, and experienced engineers are easier to find.



9

IS-IS versus OSPF - Terminology

Hello packetIIH (IS-to-IS Hello Packet)

BDRN/A

DR

(Designated Router)

DIS

(Designated Intermediate System)

PacketPDU

(Protocol Data Unit)

Datalink AddressSNPA

(Subnetwork Point of Attachment)

LinkCircuit

RouterIS (Intermediate System)

HostES (End System)

CommentsOSPFIS-IS

10

IS-IS versus OSPF - Terminology

IS-IS uses a backbone path connected by contiguous L2 routers. There is no backbone area in IS-IS

Backbone area (Area 0)

Level 2 Area

Area (non-backbone)

Level 1 Area

The term routing domain is also used with OSPF.

AS Routing Domain

LSAck or LSR (Link State Request)

PSNP (Partial Sequence Number PDU or Packet)

DBD (Data Base Description Packet)

CNSP (Complete Sequence Number PDU or Packet)

LSAs are actually comparable to TLVs used in LSPs.

LSA (Link -State Advertisement)

LSP (Link-State Packet)

CommentsOSPFIS-IS



11

IS-IS versus OSPF – ISs (Routers)

The System ID is the key for SPF calculations. Sometimes the NET address is thought of as the Router ID.

Router IDSystem ID

AFI is part of the NSAP.RFC 1918 AddressesAFI = 49

ABRLevel 1-2 IS (router)

Any Level 2 router can distribute externals into the domain. No special name. (Cisco IOS allows Level 1 routers to distribute externals.)

Internal Backbone Router or ASBR

Level 2 IS (router)

Internal, non-backbone router in a Totally Stubby Area

Internal Non-backbone Router

Level 1 IS (router)

CommentsOSPFIS-IS


Lesson 3

Introduction to IS-IS

ProtocolRoutersAreas Levels



13

IS-IS Link-State Operation

Routers identified as Level 1, Level 2, or Level 1-2:

� Level 1 routers use LSPs to build topology for local area.

� Level 2 routers use LSPs to build topology between different areas.

� Level 1-2 routers act as border routers between Level 1 and Level 2 routing domains.

14

Integrated IS-IS Design Principles

� IP and CLNP addressesmust be planned.

� Use two-level hierarchy for scalability:

Limits LSP flooding

Provides opportunity for summarization

� Summarization:

Limits update traffic

Minimizes router memory and CPU usages



15

Four OSI Routing Levels

16

OSI Routing Protocols: ES-IS and IS-IS

ES-IS

� Analogous to Address Resolution Protocol (ARP) in IP

� Not technically a routing protocol

� Sometimes referred to as Level 0 routing.

� ESs (hosts) discover nearest IS (router) by listening to IS Hello (ISH) packets

� ISs (routers) know which hosts are on their subnetwork by listening to ES Hello (ESH) packets.

� Not applicable for IP networks

ISH ESH



17

OSI Routing Protocols: ES-IS and IS-IS

IS-IS

� OSI distinguishes between Level 1, Level 2, and Level 3 routing.

� Level 1 Routing

If DA (destination address) is an ES on another subnetwork in the same area, the IS knows the correct route and forwards packet appropriately.

� Level 2 Routing

If DA is an ES on another area, the Level 1 IS sends the packet to the nearest Level 2 IS.

� Level 3 Routing is between separate domains.

Pure CLNS environment IDRP or ISO-IGRP can be used, in IP, BGP is used.

(Not applicable to CCNP)

Boundary areas in

IS-IS exists on a link

between routers and

not on a router itself

as in OSPF.

These routers should

be entirely in Area 1

and Area 2.

18

IS-IS Areas

IS-IS Routers:

� Level 1 IS (L1 IS, router)

Analogous to OSPF Internal non-backbone router (Totally Stubby)

Responsible for routing to ESs inside an area.


Analogous to OSPF Internal Backbone router

Responsible for routing between areas

� Level 1 and Level 2 IS (L1-L2 IS, router)

Analogous to OSPF ABR router

Participate in both L1 intra-area routing and L2 inter-area routing.



19

Level 1 Router


Analogous to OSPF Internal non-backbone router (Totally Stubby)

Responsible for routing to ESs inside an area.

� A contiguous group of Level 1 routers define an area.

� Level 1 routers maintain the Level 1 database for the area and exit points to neighboring areas.

20

Level 2 Router


Analogous to OSPF Internal Backbone router

Responsible for routing between areas

� Also referred to as area routers.

� Interconnect the Level 1 areas

� Store separate database of only inter-area topology



21

Level 1 – Level 2Router

� Level 1 and Level 2 IS (L1-L2 IS, router)

Analogous to OSPF ABR router

Participate in both L1 intra-area routing and L2 inter-area routing.

� Maintain both Level 1 and Level 2 LSDB

� Support Level 1 function communicating with other Level 1 routers in their area

Inform other Level 1 routers that they are the exit point (default route) from the area.

� Support Level 2 function communicating with the rest of the backbone path.

22

IS-IS Backbone

� IS-IS does not share the concept of a backbone area 0 with OSPF.

� An IS-IS backbone can appear as a set of distinct areas interconnected by a chain of Level 2 routers, weaving their way through and between the Level 1 Areas.

� The IS-IS backbone (path) consists of a contiguous set of Level 1-2 and Level 2 routers.

� Where is the backbone (path)?



23

Hierarchy

� IS-IS has 2 layers of hierarchy

The backbone is called level-2

Areas are called level-1

� Same algorithms apply for L1 and L2

� A router can take part in L1 and L2

Inter-area routing (or inter-level routing)

24

Adjacency levels (later)

L1-Adjacency L2-Adjacency

L2-AdjacencyL2-Adjacency

L1L2

Adjacency

L1L2

Adjacency

Router with adjacencies within

the same area.

However, needs to have a L2

database as well since it is a transit

node

Therefore L1L2 adjacency is required



25

Level-1, Level-2 & Level-1-2 Routers

•Backbone MUST BE L2 contiguous

L1-only

L1-only

L1-only

L1-only

L1-L2

L1-L2

L2-only

L1-only

L1-L2

L1-L2

L1-only

This router has to behave as level-2

as well in order to guarantee backbone

continuity

26

Level-1, Level-2 & Level-1-2 Routers

L1-only

L1-only

L1-only

L1-L2

L1-L2

L2-only

L1-L2

L1-L2

L1-only

This router has to behave as level-2

as well in order to guarantee backbone

continuity

L1-L2

•Backbone MUST BE L2 contiguous



27

ISIS router cannot determine if they need to be L1 or L1L2

Therefore By default all cisco routers will behave as L1L2

Area 4

Can an IS determine its level ?

Area 3

Area 2

Area 1

“I’m in area 2 and ALL

my neighbors are in the

same area. I must be a

L1-only router ?”

!! NO !!

Rtr C must have a full L2 LSDB

to route between areas 1, 3 and

4. Remember, the backbone

must be contiguous.


Lesson 3

OSI Addressing

NSAP (Area, System ID, NSEL)

LSPids

SNAP



29

OSI terminology

� SNPA = @MAC

� NSAP = @IP

NET = @IP que identifica el node (router)

� ES-IS = ARP

� ES = Host

� IS = Router

� Domain = AS

� Area = Area (OSPF)

30

NSAPs and Addressing

� NSAP=Network Service Access Point

� The NSAP is the network layer address for CLNS packets

� One NSAP per box, not per interface (similar to DECnet)

� SNPA means SubNetwork Point of Attachment, which is the layer2 or MAC address



31

How do I read an NSAP ?

� An NSAP consists of 3 parts

Area-address, systemID and n-selector

� Total length between 8 and 20 bytes

Example: 49.0001.0000.0000.0007.00

� Authority and Format ID+InterDomain ID = InterDomain Part

� High-Order Domain Specific Part == Subnets

� System ID == Station

� NSEL == Application

32

NSAPs

� Format of the Cisco NSAP address consists of three parts.

Area address

System ID

NSAP selector byte

� Area address is a variable length field

� The system ID is the ES or IS identifier in an area, similar to the OSPF router ID.

The system ID has a fixed length of six bytes as engineered in the Cisco IOS.

� The NSAP selector byte is a service identifier.

Analogous to that of a port or socket in TCP/IP.



33

How do I read an NSAP ?

34

Do I need an NSAP if I want to use IS-IS for IP routing ?

� Yes, still needed for IP routing only

� Area address is like OSPF area

� SystemID is like an OSPF routerID

LSP identifier is derived from systemID



35

Creating unique systemIDs

� SystemID is 6 bytes

� Start numbering 1, 2, 3, 4 …. etc

� Convert your loopback IP address

192.31.231.16 -> 192.031.231.016 -> systemID 1920.3123.1016

36

Creating area addresses

� If you do CLNS routing, request an official NSAP prefix

� If you do just IP routing, use AFI 49

� AFI 49 denotes private address space

like network 10.0.0.0 in IP

� Just number your areas 49.0001… 49.0002…., 49.0003,… etc



37

NSAPs – Cisco Format

NSEL (NSAP Selector)

� NSEL is a service identifier.

� Loosely equivalent to that of a port or socket in TCP/IP.

� Must be specified by a single byte preceded by a period (.)

� Not used in routing decisions.

NET

� When NSEL = 00, it identifies the device itself, the network level address.

� The NSAP with a NSEL = 00 is known as a Network Entity Title (NET)

� A NET is an NSAP with the NSEL set to (00)

Area – System ID – NSEL

49.0001.2222.2222.2222.00

38

NSAP (NETs)

Example 1: NSAP 47.0001.aaaa.bbbb.cccc.00

� Area ID is 47.0001

� System ID is aaaa.bbbb.cccc

� NSAP selector byte is 00

Example 2: NSAP 39.0f01.0002.0000.0c00.1111.00

� Area ID is 39.0f01.0002

� System ID is 0000.0c00.1111

� NSAP selector byte is 00

Other Examples

Area – System ID – NSEL

49.0001.2222.2222.2222.00



39

Configuring IS-IS (so far)

� ip router isis: IS-IS must be enabled on the interface

� Note: IS-IS routing cannot be enabled on an interface until an IP addresshas been configured on the interface.

SanJose1

interface FastEthernet0/0

ip address 172.16.0.1 255.255.255.0

ip router isis

router isis

net 49.0001.1111.1111.1111.00

SanJose2


ip address 172.16.0.2 255.255.255.0

ip router isis

router isis

net 49.0001.2222.2222.2222.00

Area . System ID . NSEL

SanJose3


ip address 172.16.0.3 255.255.255.0

ip router isis

router isis

net 49.0001.3333.3333.3333.00

Area

49.0001

40


� To display both ES and IS neighbors.

� SNPA is the MAC address of the remote router.

If serial, would show encapsulation, I.e. HDLC

� Cisco routers default to L1-L2 type routers.

� We will see how to change this in a moment.

Area

49.0001



41

Level-1 routing

� L1-only routers know only topology of their own area (including allISs and ESs in the area)

� L1L2 ISs set the “attached-bit” in their L1-LSP header

L1-only routers look at the attach-bit (ATT) in L1 LSPs to find the closest L1L2 router

� L1-only routers install a default route to the closest L1L2 router in the area

Traffic to other areas is sent via the closest L2 IS

42

The Attached bit

Area 2 Area 1

rtr A

rtr D

� L1L2 routers set the ATT bit in their L1 LSP

� L1 routers use ATT bit found in L1-LSDB as possible area exit point

ISIS for IP: level-1 router will install a 0.0.0.0/0 route towards the L1L2 with ATT-bit set

� Shortest metric to the L1L2 who sets the ATT bit wins

L2-LSDB

rtrA.00-00

rtrD.00-00

L1-LSDB

rtrA.00-00 ATT-bit

rtrB.00-00

rtrC.00-00

L1-LSDB

rtrD.00-00 ATT-bit

rtrE.00-00

rtrF.00-00



43

Suboptimal Routing


Lesson 3

IS-IS Adjacencies

Are we half way yet?



45

Hello Messages

� IS-IS uses Hello PDUs to establish adjacencies with other routers (ISs) and ESs.

� IS-IS has three types of Hello PDUs:

ESH, sent by ES to an IS

ISH, sent by IS to an ES

IIH, used between two ISs (CCNP 1)

Hello Level 1 LAN

Hello Level 2 LAN

Hello Point-to-Point

46

Neighbors and Adjacencies

� IS-IS discover neighbors and forms adjacencies using IS-IS Hello PDUs.

� Transmitted every 10 seconds

� Can be changed using the interface command, is hello-interval

� Hold time defaults to 3 times the Hello time (30 seconds), before declaring a neighbor dead.

Changed using the interface command is hello-multiplier

Default is 3



47

LAN Representation and Adjacencies

� Similar to the DR in OSPF…

� DIS (Designated IS) is elected to generate the LSP (Link State Packet, ie. LSA) representing the virtual router connecting all attached routers to a star-shaped topology.

� For SPF, the whole network must look like a collection of nodes and point-to-point links.

� LAN uses a virtual node called pseudonode.

DIS

48

LAN Representation and Adjacencies

� Election of DIS:

Router with highest priority (Cisco default is 64)

Router with highest MAC address

� No “BDR”

� No way to make a router ineligible from being DIS (no OSPF priority 0)

� New router (IS) can cause a new election, unlike OSPF

� Used as circuit ID for all routers on LAN.

� Periodically broadcasts CSNPs (OSPF DBD) every 10 seconds

� Each router on the LAN simulates an interface on the pseudonode.

DIS



49

Identifying nodes in a LSP

� In IS-IS Nodes are identified by 7 bytes. SystemIDs are 6 bytes and NSEL is 1 byte.

A normal node (non-pseudonode) is identified by 6 bytes systemID plus a zero.

00c0.0040.1234.00-00

A pseudonode is identified by the systemID of the DIS, plus 1 byte from the circuitID of the interface of the DIS.

00c0.0040.1234.01-00

50

A pseudonode on a LAN

Logical view

LAN

Physical view

DIS

Pseudonode

DIS

� For SPF, the whole network must look like a collection of nodes and point-to-point links.

� Assume a virtual node for the LAN

This virtual node is called pseudonode. It is not a real router, but just an extra LSP in the LSPDB



51

Who creates the pseudonode?

� Created by Designated Router (DIS)

� No Backup Designated Router in IS-IS

� The DIS reports all LAN neighbours in the pseudonode LSP; with metric 0

� All LAN routers report connectivity to the pseudonode in their LSPs

52

Adjacencies

� L1 routers form L1 adjacencies with L1 and L1-L2 routers in their area.

� L2 routers form L2 adjacencies with L2 and L1-L2 routers in their area or another area.

� L1L2 routers form L1 and L2 adjacencies with each other in theirarea or another area.

� L1 router does not form an adjacency with an L2 router

LAN

Adjacencies



53

WAN Adjacencies

� On point-to-point links the IIH PDUs are common to both Level 1 and Level 2.

� Announce both their Level type and Area ID in the Hellos.

� Remember, separate LSDBs for different Levels.

� What are the adjacencies? L1? L2? L1L2? None?

54

� What are the adjacencies? L1? L2? L1L2? None?

� The adjacencies also determine what type of routes the IS (router) will have in its routing table.

L1 – Intra-area routes (routes only within that area)

L2 – Inter-area routes (routes from other areas)

Or both

WAN Adjacencies



55


� isis priority: Sets DIS priority on a LAN interface, default 64

SanJose1


ip address 172.16.0.1 255.255.255.0

ip router isis

isis priority 100

router isis

net 49.0001.1111.1111.1111.00

SanJose2


ip address 172.16.0.2 255.255.255.0

ip router isis

router isis

net 49.0001.2222.2222.2222.00

Area . System ID . NSEL

SanJose3


ip address 172.16.0.3 255.255.255.0

ip router isis

router isis

net 49.0001.3333.3333.3333.00

Area

49.0001

DIS


Lesson 3

LSP flooding



57

Only 4 types of IS-IS packets

� IS-IS Hello packet (IIH)

� Link State Packet (LSP)

� Partial Sequence Number Packet (PSNP)

� Complete Sequence Number Packet (CSNP)

� Packets are sometimes called Protocol Data Units (PDU in OSI)

58

IS-IS Hello PDUs

� Also called IIHs

� Used for maintaining adjacencies

� Different on p2p links and LANs

� Different from ISHs and ESHs (ES-IS)

� IIHs are padded to full MTU size



59

Link State PDUs

� Called LSPs

� Contains all info about one router

Adjacencies, connected IP prefixes, OSI endsystems, area addresses, etc.

� One LSP per router (plus fragments)

� One LSP per LAN network

60

Sequence Number PDUs

� Partial (PSNP) and Complete (CSNP)

� Used when flooding the LSPDB

� PSNPs are like ACKs on p2p links

� CSNPs are used for LSPDB synchronization over LANs

� CSNP are also used to sync LSPDB over new p2p adjacencies

LSAck or LSR (Link State Request)

PSNP (Partial Sequence Number PDU or Packet)

DBD (Data Base Description Packet)

CNSP (Complete Sequence Number PDU or Packet)

LSA (Link -State Advertisement)LSP (Link-State Packet)

OSPFIS-IS



61

Why do we need flooding?

� All routers generate an LSP

� All LSPs need to be flooded to all routers in the network

If LSPDB is not synchronised, routing loops or blackholesmight occur

� IS-IS’ two components are the SPF computation and reliable flooding

62

What triggers a new LSP ?

� When something changes …

Adjacency came up or went down

Interface up/down (connected IP prefix !)

Redistributed IP routes change

Inter-area IP routes change

An interface is assigned a new metric

Most other configuration changes

Periodic refresh



63

Basic flooding rules

� When receiving an LSP, compare with old version of LSP in LSPDB

� If newer:

Install it in the LSPDB

Acknowledge the LSP with a PSNP

Flood to all other neighbours

Check if need to run SPF

� If same age:


� If older:


Send our version of the same LSP

Wait for PSNP

64

Sequence number

� Each LSP (and LSP fragment) has its own sequence number

� When router boots, sets seqnr to one

� When there is a change, the seqnr is incremented, a new version of the LSP is generated with the new seqnr

� Higher seqnr means newer LSP



65

Flooding on a P2P Link

RouterA

RouterB

Received ack

Clear SRMbit

(Send Routing

Message)

Received it. Local

copy has seqNr = 21.

So the received one is

newer. Install it in LSDB.

Acknowledge it. Maybe

flood further.id=x seqnr=22

PSNP

Now flood it:

Set SRM bit.

Send over p2p.

id=x seqnr=22

LSP

Receives LSP

id=x seqNr=22

It’s new. Put it in

the LSPDB

id=x seqnr=22

LSP

66

The Designated IS

� DIS is like the DR in OSPF

� DIS is only on LANs, not on p2p

� DIS has two tasks

Create/update pseudonode LSP

Conduct flooding over the LAN

� DIS sends periodic CSNPs

LSPid, SeqNr, Checksum, Lifetime of all LSPs present in the LSPDB

� No Backup DIS in ISIS

� DIS is elected by priority and MAC

Actually is “self-elected”

� LAN circuitID shows who is DIS

Use show clns interface



67

Flooding on a LAN

Periodic CSNP

every 10 secs

id=y seqnr=...

id=x seqNr=22

id=z ...

CSNP

LAN

DISRtr-A

Got it. Install and

run SPF

Local copies of LSP-y and

LSP-z are up-to-date but

local copy of LSP-x is older.

Request latest LSP-x via

PSNP

id=x seqNr=21

PSNP

!!! Problem !!!

Dropped LSP

LSP

Received new LSP

id=x seqNr=22

Install in LSPDB.

Flood the LSP.

id=x seqNr=22

LSP

Neighbor has an

old LSP, better

resend him latest

id=x seqNr=22

LSP


Lesson 3

IP routing specifics



69

ISIS routing Levels

L1

L1L2

L1

L1L2L1

2. Level-1 LSP with

IP prefix: 10.1.0.0/16

2. Level-1 LSP with

IP prefix: 10.10.0.0/16

L1

1. Level-1 LSP with

Attached-bit (used

as a default route by

all level-1routers

3. Level-2 LSP with

IP prefix: 10.1.0.0/16

IP prefix: 10.10.0.0/16

Routers within an area do not

have any routing information

about prefixes originated outside

the area. Default routing (ATT-bit

or explicit 0.0.0.0/0) is used to reach

destinations outside the area.

70

ISIS routing Levels

L1L2

L1

L2L2

L1L2

L1

L1L2

L1

1. Level-1 LSP with

IP prefix: 10.1.0.0/16

4. At this point the prefix

10.1.0.0/16 will NOT be inserted

in the L1 LSP (no route leaking

by default)

2. Level-2 LSP with

IP prefix: 10.1.0.0/16 2. Level-2 LSP with

IP prefix: 10.1.0.0/16

3. Level-2 LSP with

IP prefix: 10.1.0.0/16

3. Level-2 LSP with

IP prefix: 10.1.0.0/16

2. At this point prefix

10.1.0.0/16 will be

inserted in L2 LSP

2. At this point prefix

10.1.0.0/16 is

inserted in L2 LSP

0. Level-1 LSP with

ATT bit set

0. Level-1 LSP with

ATT bit set

0. Level-1 LSP with

ATT bit set




Lesson 3

Configuration, Show,& Debug Commands

72

Router-B--------------

interface Loopback0

ip address 192.168.1.1 255.255.255.255

!

Interface Serial0

ip address 192.168.120.10 255.255.255.0

ip router isis

!

interface Serial1

ip address 192.168.222.1 255.255.255.0

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 Serial0

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

Basic Configuration

Area 49.0001

Rtr-A

Rtr-B

L1L2 routers

L1router

Area 49.0002

Rtr-C

L1router

S0

S1

S0

S1

S0

S1

Rtr-D



73

Router-C--------------

interface Loopback0

ip address 192.168.2.2 255.255.255.255

!

interface Serial0

ip address 192.168.111.2 255.255.255.0

ip router isis

isis circuit-type level-1

!

interface Serial1

ip address 192.168.222.2 255.255.255.0

ip router isis

isis circuit-type level-2

!

router isis


net 49.0002.1921.6800.2002.00

Router-D--------------

interface Loopback0

ip address 192.168.2.4 255.255.255.255

!

interface Serial1

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

Basic Configuration

Area 49.0001

Rtr-A

Rtr-B

L1L2 routers

L1router

Area 49.0002

Rtr-C

L1router

S0

S1

S0

S1

S0

S1

Rtr-D

74

Troubleshooting Commands: CLNS

show clns

Router#

� Displays information about the CLNS network

show clns [area-tag] protocol

Router#

� Lists the protocol-specific information

show clns interface [type number]

Router#

� Lists the CLNS-specific information about each interface

show clns [area-tag] neighbors [type number] [detail]

Router#

� Displays both ES and IS neighbors



75

Troubleshooting Commands: CLNS and IS-IS

show isis [area-tag] route

Router#

� Displays IS-IS Level 1 routing table (system IDs)

show clns route [nsap]

Router#

� Displays IS-IS routing table (areas)

show isis [area-tag] database

Router#

� Displays the IS-IS LSDB

show isis [area-tag] topology

� Displays IS-IS least-cost paths to destinations

Router#

76

Rtr-B# show clns

Global CLNS Information:

2 Interfaces Enabled for CLNS

NET: 49.0001.1921.6800.1001.00

Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64

ERPDU's requested on locally generated packets

Running IS-IS in IP-only mode

Show clns

Area 49.0001 Area 49.0002

Rtr-B

Rtr-D

L1L2 routers

L1routers

S0

S1 S0

S0 S1

S1

Rtr-C

Rtr-A



77

Rtr-B# show clns protocol

IS-IS Router: <Null Tag>

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:

Serial1 - IP

Serial0 - IP

Redistribute:

static (on by default)

Distance for L2 CLNS routes: 110

Show clns protocol

Area 49.0001

Rtr-A

Rtr-B

L1L2 routers

L1router

Area 49.0002

Rtr-C

L1router

S0

S1

S0

S1

S0

S1

Rtr-D

78

Rtr-B# show clns neighbors

System Id Interface SNPA State Holdtime Type Protocol

Rtr-C Se0 *HDLC* Up 23 L2 IS-IS

1921.6800.1005 Se1 *HDLC* Up 21 L1 IS-IS

Show clns neighbors

Area 49.0001 Area 49.0002

Rtr-B

Rtr-D

L1L2 routers

L1routers

S0

S1 S0

S0 S1

S1

Rtr-C

Rtr-A



79

Area 49.0001

Rtr-A

Rtr-B

L1L2 routers

L1router

Area 49.0002

Rtr-C

L1router

S0

S1

S0

S1

S0

S1

Rtr-D

Rtr-B# show clns int serial1

Serial1 is up, line protocol is up

Checksums enabled, MTU 1500, Encapsulation HDLC

ERPDUs enabled, min. interval 10 msec.

CLNS fast switching enabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Next ESH/ISH in 47 seconds

Routing Protocol: IS-IS

Circuit Type: level-1-2

Interface number 0x2, local circuit ID 0x101

Level-1 Metric: 10, Priority: 64, Circuit ID: 1921.6800.1005.00

Number of active level-1 adjacencies: 1

Level-2 Metric: 10, Priority: 64, Circuit ID: Rtr-B.01


Next IS-IS Hello in 6 seconds

Show clns interface

80

Area 49.0001

Rtr-A

Rtr-B

L1L2 routers

L1router

Area 49.0002

Rtr-C

L1router

S0

S1

S0

S1

S0

S1

Rtr-D

Rtr-B# show clns int serial0

Serial0 is up, line protocol is up

Checksums enabled, MTU 1500, Encapsulation HDLC

ERPDUs enabled, min. interval 10 msec.

CLNS fast switching enabled

CLNS SSE switching disabled

DEC compatibility mode OFF for this interface

Next ESH/ISH in 30 seconds

Routing Protocol: IS-IS

Circuit Type: level-1-2

Interface number 0x1, local circuit ID 0x100

Level-1 Metric: 10, Priority: 64, Circuit ID: Rtr-C.01


Level-2 Metric: 10, Priority: 64, Circuit ID: Rtr-B.00


Next IS-IS Hello in 6 seconds

Show clns interface



81

Show clns traffic

IS-IS: Level-2 Hellos (sent/rcvd): 285/0

IS-IS: PTP Hellos (sent/rcvd): 420/415

IS-IS: Level-1 LSPs sourced (new/refresh): 8/2

IS-IS: Level-2 LSPs sourced (new/refresh): 9/1

IS-IS: Level-1 LSPs flooded (sent/rcvd): 5/8

IS-IS: Level-2 LSPs flooded (sent/rcvd): 7/8

IS-IS: LSP Retransmissions: 0

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

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

IS-IS: Level-1 PSNPs (sent/rcvd): 7/4

IS-IS: Level-2 PSNPs (sent/rcvd): 7/5

IS-IS: Level-1 DR Elections: 1

IS-IS: Level-2 DR Elections: 1

IS-IS: Level-1 SPF Calculations: 7

IS-IS: Level-2 SPF Calculations: 9

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

IS-IS: Level-2 Partial Route Calculations: 5

IS-IS: LSP checksum errors received: 0

IS-IS: Update process queue depth: 0/200

IS-IS: Update process packets dropped: 0

L1L2 routers

Area 49.0001

Rtr-A

Rtr-B

L1router

Area 49.0002

Rtr-C

L1router

S0

S1

S0

S1

S0

S1

Rtr-D

82

Example: Is Integrated IS-IS Running?

R2#show ip protocols

Routing Protocol is "isis"

Invalid after 0 seconds, hold down 0, flushed after 0

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Redistributing: isis

Address Summarization:

None

Maximum path: 4

Routing for Networks:

FastEthernet0/0

Loopback0

Serial0/0/1

Routing Information Sources:

Gateway Distance Last Update

10.10.10.10 115 00:00:02

10.30.30.30 115 00:00:03

Distance: (default is 115)

� Displays the parameters and current state of the active routing protocol processes



83

Example: Are There Any IP Routes?

R2#show ip route isis

10.0.0.0/24 is subnetted, 5 subnets

i L2 10.30.30.0 [115/45] via 10.2.2.3, Serial0/0/1

i L1 10.10.10.0 [115/20] via 10.1.1.1, FastEthernet0/0

R2#

� Displays the current state of the routing table

show ip route [address [mask]] | [protocol [process-id]]

router#

84

Q and A



85

what is is-is - salleurl.eduusers.salleurl.edu/~zaballos/ccnp/4.pdf(not applicable to ccnp) boundary...

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