the is-is protocol

© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 4 Lesson 1 1

The IS-IS Protocol

SAvPS

Genci

© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 2BSCI Module 4 Lesson 1

References

Intermediate System-to-Intermediate System Protocol www.cisco.com

CNAP presentation

Presentation of P. Paluch (fri.utc.sk)


Reasons why to uses IS-IS Routing

Large ISPs

Stable protocol

Originally deployed by ISPs because US government mandated internet support of OSI and IP


Úvod do OSI sietí

Na prelome 70. a 80. rokov 20. storočia sa vývoj uberal dvomi smermi:

• US Department of Defense vyvíjal tzv. Network Control Program, ktorý bol neskôr nahradený súčasnou sadou protokolov TCP/IP

• ISO sa snažila vytvoriť a štandardizovať vlastnú sadu protokolov – tzv. OSI stack, ktorý zodpovedá známemu RM ISO OSI

Zatiaľčo pragmatici programujúci TCP/IP jednoduchosťou a prehľadnosťou protokolu uspeli, ISO sa zdržovala vytváraním formálnych, komplexných a abstraktných protokolov a rozhraní medzi nimi

• Protokoly ISO sú pomerne komplikované, ich štandardizácia sa dlhý cas vliekla

• ISO protokoly dodnes možno nájsť v sieťach telekomunikačných operátorov, avšak masové nasadenie ISO protokolov nikdy nenastalo


Intro to OSI Networks - History


Úvod do OSI sietí

Pre OSI siete boli navrhnuté niekolké smerovacie protokoly:

• ES-IS: komunikácia medzi stanicou a jej bránou

• IS-IS: komunikácia medzi routermi v jednom autonómnom systéme (v ISO terminológii „doména“)

• IDRP: komunikácia medzi doménami (analóg BGP)

Vlastnosti IS-IS sa ukázali ako dobré a premyslené

• IS-IS bol navrhovaný a funkcný skôr než OSPF a OSPF štartovalo ako lahký odvar IS-IS

• Pri migrácii existujúcich OSI sietí na IP bolo vhodnejšie mat protokol, ktorý dokáže naraz slúžit aj pre OSI, aj pre IP

• Do IS-IS boli v RFC 1195 dodefinované rozšírenia pre spoluprácu s IP svetom, sémantika protokolu však zostala


ISO Protocol Suite


ISO OSI Connectionless Network Service

OSI CLNS (Connectionless Network Service) is a network layer service similar to the IP service.

A CLNS entity communicates over Connectionless Network Protocol (CLNP) with its peer CLNS entity.

Routers are ISs, and hosts are End Systems (ESs).

ESs themselves have no routing information;

• they discover ISs (routers) by listening to Intermediate System Hellos (ISHs) and sending traffic to any random router.

• ESs send End System Hellos (ESHs);

• they do not choose a designated router to handle all traffic,

• optimal routing is accomplished via redirects


CLNS Terminology


Four OSI Routing Levels


ISO Addressing

CLNS addresses that are used by routers are called network service access points (NSAPs)

NSAP addresses have a size from 8 to 20 bytes

NSAP address contains OSI address of the device and link to the higher layer process


NSAP Address Formats


ISO Address Structure


Network Entity Title (NET Address)

NSAP addresses have a one-octet NSEL field that identifies a process on the device

NET addresses are NSAP addresses with an NSEL value of 0


Example


Continue – Paluch sl. 11


IS-IS Routing

IS = router

IS-IS was originally designed as the IGP for the Connectionless Network Service (CLNS), part of the OSI protocol suite.

The OSI protocol suite layer 3 protocol is the Connectionless Network Protocol (CLNP).

IS-IS uses CLNS addresses to identify routers and build the LSDB.


IS-IS Features

Link-state routing protocol

Supports VLSM

Uses Dijkstra’s SPF algorithm; has fast convergence

Uses Hellos to establish adjacencies and LSPs to exchange link-state information

Efficient use of bandwidth, memory, and processor

Supports two routing levels:Level 1: Builds common topology of system IDs in local area and routes within area using lowest cost path.

Level 2: Exchanges prefix information (area addresses) between areas. Routes traffic to area using lowest-cost path.


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.


Integrated IS-IS Routing

Integrated IS-IS is IS-IS for multiple protocols:

For IP, CLNS, or both

Uses its own PDUs to transport IP routing information; updates are not sent in IP packets.

Requires CLNS addresses, even if only routing for IP.


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


Issues with Integrated IS-IS

Default narrow metrics are limited to 6-bit interface and

10-bit path metric:In Cisco IOS 12.0, wide metrics allow 24-bit interface and 32-bit path metric.

Cisco IOS software has default metric of 10 on all interfaces.


End System-to-Intermediate System

ES-IS forms adjacencies between ESs and routers (ISs).IP end-systems don’t use ES-IS

ESs transmit ESHs to announce their presence to ISs.

ISs transmit ISHs to announce their presence to ESs.

ISs transmit IIHs to other ISs.


Four OSI Routing Levels


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.


Integrated IS-IS vs. OSPF: Area Design

OSPF is based on a central backbone with all areas attached to it.

In OSPF the border is inside routers (ABRs)

Each link belongs to one area


Advantages of Integrated IS-IS

Supports CLNP and IP

More extensible through TLV design


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.


Comparison of Integrated IS-IS and OSPF

OSPF Integrated IS-IS

Area border inside routers (ABRs) Area border on links

Each link in only 1 area Each router in only 1 area

More complex to extend backbone Simple extension of backbone

Many small LSAs sent Fewer LSPs sent

Runs on top of IP Runs on top of data-link layer

Requires IP addresses Requires IP and CLNS addresses

Default metric is scaled by interface bandwidth

Default metric is 10 for all interfaces

Not easy to extend Easy to support new protocols with new TLV tuples

Equipment, personnel, and information more readily available

Equipment, personnel, and information not as easily available

The following table summarizes the differences between OSPF and integrated IS-IS.

© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 4 Lesson 1 31

The IS-IS Protocol

BSCI Module 4 Lesson 3

Configuring Basic Integrated IS-IS


OSI Area Routing: Building an OSI Forwarding Database (Routing Table)

When databases are synchronized, Dijkstra’s algorithm (SPF) is run on the LSDB to calculate the SPF tree.

The shortest path to the destination is the lowest total sum of metrics.

Separate route calculations are made for Level 1 and Level 2 routes in Level 1-2 routers.

Best paths are placed in the OSI forwarding database (CLNS routing table).


Building an IP Routing Table

Partial Route Calculation (PRC) is run to calculate reachability.

Since IP and ES are represented as leaf objects, they do not participate in SPF.

Best paths are placed in the IP routing table following IP preferential rules.

They appear as Level 1 or Level 2 IP routes.


Integrated IS-IS Configuration Steps

1. Define areas, prepare addressing plan (NETs) for routers, and determine interfaces.

2. Enable IS-IS on the router.3. Configure the NET.4. Enable Integrated IS-IS on the appropriate

interfaces. Do not forget interfaces to stub IP networks, such as loopback interfaces (although there are no CLNS neighbors there).

These are each explained in the next few slides.


Integrated IS-IS Routing Three Basic Commands

Command Description

router isis [area-tag]

Enables IS-IS as an IP routing protocol and assigns a tag to the process (optional). Given in the global configuration mode.

net network-entity-title

Identifies the router for IS-IS by assigning a NET to the router. Given in the router configuration mode.

ip router isis [area-tag]

Enables IS-IS on the interfaces that run IS-IS. (This approach is slightly different from most other IP routing protocols, where the interfaces are defined by network statements; there is no network statement under the IS-IS process.) Given in interface configuration mode.


Step 1: Define Area and Addressing

Area determined by NET prefix:Assign to support two-level hierarchy.

Addressing:IP:Plan to support summarization.

CLNS: Prefix denotes area. System ID must be unique.


Step 2: Enable IS-IS on the Router

Enable the IS-IS routing protocol.area-tag – name for a process

When routing of CLNS packets is also needed, use the clns routing command.

router isis [area-tag]

router(config)#


Step 3: Configure the NET

Configure an IS-IS NET address for the routing process.

net network-entity-title

Router(config-router)#


Step 4: Enable Integrated IS-IS

ip router isis [area-tag]

router(config-if)#

Includes an interface in an IS-IS routing process


Simple Integrated IS-IS ExampleThe configured router acts as an IP-only Level 1-2 router.

interface FastEthernet0/0 ip address 10.1.1.2 255.255.255.0 ip router isis!interface Serial 0/0/1 ip address 10.2.2.2 255.255.255.0 ip router isis!

<output omitted>

router isis net 49.0001.0000.0000.0002.00


Change IS-IS Router Level

is-type {level-1 | level-1-2 | level-2-only}


Configure the IS-IS level globally on a router; the default is level 1-2.


Change IS-IS Interface Level

isis circuit-type {level-1 | level-1-2 | level-2-only}

Router(config-if)#

Configure the type of adjacency on an interface; the default is Level 1-2.


Change IS-IS Metric

Configure the metric for an interface; the default is 10.

Metric value is from 1 to 63.


metric default-value {level-1 | level-2}

Alternately, configure the metric globally for all interfaces.

isis metric metric [delay-metric [expense-metric [error-metric]]] {level-1 | level-2}

Router(config-if)#


Example: Tuning IS-IS Configuration

Change router type on R1 and R3

Change interface levels on R2

Change metric on S0/0/1


IP Summarization

summary-address address mask [level-1 | level-2 |level-1-2][tag tag-number] [metric metric-value]


P3R1(config-router)# summary-address 10.3.2.0 255.255.254.0 level-1-2

Creates summary Default is Level 2

Example:

Summarizes 10.3.2.0/23 into Level 1-2


Example: Is Integrated IS-IS Running?R2#show ip protocolsRouting 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


Example: Are There Any IP Routes?

R2#show ip route isis 10.0.0.0/24 is subnetted, 5 subnetsi L2 10.30.30.0 [115/45] via 10.2.2.3, Serial0/0/1i L1 10.10.10.0 [115/20] via 10.1.1.1, FastEthernet0/0R2#

Displays the current state of the routing table

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

router#


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


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#


Example: OSI Intra-Area and Interarea Routing

Routing in a Two-Level Area Structure


Level 1 and Level 2 Topology Table

R1#show isis topologyIS-IS paths to level-1 routersSystem Id Metric Next-Hop Interface SNPAR1 --R2 10 R2 Fa0/0 0016.4650.c470

R2#show isis topologyIS-IS paths to level-1 routersSystem Id Metric Next-Hop Interface SNPAR1 10 R1 Fa0/0 0016.4610.fdb0R2 --IS-IS paths to level-2 routersSystem Id Metric Next-Hop Interface SNPAR1 **R2 --R3 35 R3 Se0/0/1 *HDLC*


Simple Troubleshooting:What About CLNS Protocol?

R2# show clns protocol

IS-IS Router: <Null Tag> System Id: 0000.0000.0002.00 IS-Type: level-1-2 Manual area address(es): 49.0001 Routing for area address(es): 49.0001 Interfaces supported by IS-IS: Loopback0 - IP Serial0/0/1 - IP FastEthernet0/0 - IP Redistribute: static (on by default) Distance for L2 CLNS routes: 110 RRR level: none Generate narrow metrics: level-1-2 Accept narrow metrics: level-1-2 Generate wide metrics: none Accept wide metrics: none


Are Adjacencies Established?R2# show clns neighborsSystem Id Interface SNPA State Holdtime Type ProtocolR3 Se0/0/1 *HDLC* Up 28 L2 IS-ISR1 Fa0/0 0016.4610.fdb0 Up 23 L1 IS-IS

R2#show clns interface s0/0/1Serial0/0/1 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 45 seconds Routing Protocol: IS-IS Circuit Type: level-2 Interface number 0x1, local circuit ID 0x100 Neighbor System-ID: R3 Level-2 Metric: 35, Priority: 64, Circuit ID: R2.00 Level-2 IPv6 Metric: 10 Number of active level-2 adjacencies: 1 Next IS-IS Hello in 5 seconds if state UP


Summary

. Integrated IS-IS routing for IP uses CLNS and therefore

requires CLNS addresses, that is, NET addresses.

Integrated IS-IS requires planning the addresses, enabling the router, defining the router NET, and enabling the appropriate interfaces.

IS-IS can be optimized by adjusting adjacency levels and changing the default metric cost.

IS-IS summarization can be configured with the summary-address command.


Summary (Cont.)

. The show ip protocols and show ip route

commands verify the IS-IS configuration and IP functionality.

Various show commands are used to troubleshoot CLNS IS-IS structures and Integrated IS-IS networks


Activity

Using a simple three router network configuration, set up the connections using IS-IS as your routing protocol. Be sure to enable CLNS. Follow the steps in this module to complete this task.

Verify your connections by running the show commands discussed.

show ip protocols, show ip isis interfaces, show ip route; show clns neighbors, show isis topology, and show clns protocol


Self Check

How many ISIS levels are there?

Define each of the levels and what type of connections they are.

CLNS is what protocol. What is it used for?

What command displays the ISIS topology database information?


Additional Links

http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800c5bc1.html

http://www.certificationzone.com/cisco/newsletter/SL/IE-ISIS-WP2-F02_BIF.html

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfisis.htm

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Q and A

the is-is protocol

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