Tài liệu Building Scalable Cisco Internetworks pptx

BSCI

Building Scalable Cisco
Internetworks
Version 1.2

Student Guide

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Building Scalable Cisco Internetworks, Revision 1.2: Student Guide
Copyright  2001, Cisco Systems, Inc.
All rights reserved. Printed in USA.




Copyright  2001, Cisco Systems, Inc. Building Scalable Cisco Internetworking v
Table of Contents
INTRODUCTION 1-1
Overview 1-1
Course Objectives 1-2
Course Objectives (cont.) 1-3
Course Topics 1-4
Prerequisites 1-5
Participant Role 1-8
General Administration 1-10
Sources of Information 1-11
Course Syllabus 1-12
Graphic Symbols 1-14

ROUTING PRINCIPLES 2-1
Overview 2-1
Objectives 2-2
Classful Routing Protocol Overview 2-3
Classless Routing Overview 2-6
Distance Vector Operation 2-9
Link-State Operation 2-10
Written Exercise: Comparing Routing Protocols 2-29
Objective 2-29
Task 2-29
Completion Criteria 2-30
Summary 2-31
Review Questions 2-32
EXTENDING IP ADDRESSES 3-1
Overview 3-1
Objectives 3-2
IP Addressing Issues 3-3
IP Addressing Solutions 3-4
Hierarchical Addressing 3-9
VLSMs 3-11
Written Exercise 1: Calculating VLSMs 3-14
Objective 3-14
Task 3-14
Completion Criteria 3-14
Route Summarization 3-15
Written Exercise 2: Using Route Summarization 3-25
Objective 3-25
Click Here to Post Review Comments
vi Building Scalable Cisco Internetworking Copyright  2001, Cisco Systems, Inc.
Task 1 3-25

Task 2 3-26
Completion Criteria 3-26
Classless Interdomain Routing 3-27
Summary 3-29
Review Questions 3-30
CONFIGURING EIGRP 4-1
Overview 4-1
Outline 4-1
Objectives 4-2
EIGRP Overview 4-4
EIGRP Operation 4-13
Written Exercise: EIGRP Overview 4-34
Objective 4-34
Task 4-34
Completion Criteria 4-34
Configuring EIGRP 4-35
Using EIGRP in Scalable Internetworks 4-54
Verifying EIGRP Operation 4-69
Summary 4-71
Review Questions 4-73
CONFIGURING OSPF IN A SINGLE AREA 5-1
Overview 5-1
Objectives 5-2
Objectives (cont.) 5-3
OSPF Overview 5-4
OSPF Terminology 5-7
OSPF Operation 5-9
OSPF Operation in a Broadcast Multiaccess Topology 5-10
OSPF Operation in a Point-to-Point Topology 5-21
OSPF Operation in an NBMA Topology 5-22

Written Exercise: OSPF Operation 5-34
Objective 5-34
Task 5-34
Completion Criteria 5-35
Configuring OSPF in a Single Area 5-36
Verifying OSPF Operation 5-48
Summary 5-57
Summary (cont.) 5-58
Review Questions 5-59
INTERCONNECTING MULTIPLE OSPF AREAS 6-1
Overview 6-1
Objectives 6-2
Objectives (cont.) 6-3
Copyright  2001, Cisco Systems, Inc. Building Scalable Cisco Internetworking vii
Creating Multiple OSPF Areas 6-4
Routing Table Results with Different Areas 6-14
OSPF Operation Across Multiple Areas 6-15
Virtual Links Overview 6-18
Written Exercise: OSPF Operation Across Multiple Areas 6-20
Objective 6-20
Task 6-20
Completion Criteria 6-21
Using and Configuring OSPF Multiarea Components 6-22
Verifying OSPF Operation 6-40
Summary 6-42
Summary (cont.) 6-43
Review Questions 6-44
CONFIGURING IS-IS PROTOCOL 7-1
Overview 7-1
Objectives 7-2

Introduction to OSI Protocols and IS-IS Routing 7-3
Operation of IS-IS 7-28
IP and OSI Routing with Integrated IS-IS 7-53
Basic Integrated IS-IS Router Configuration 7-69
Modeling WAN Networks in Integrated IS-IS 7-83
Summary 7-97
Review Questions 7-97
OPTIMIZING ROUTING UPDATE OPERATION 8-1
Overview 8-1
Objectives 8-2
Objectives (cont.) 8-3
Redistribution Between Multiple Routing Protocols 8-4
Configuring Redistribution 8-12
Controlling Routing Update Traffic 8-27
Verifying Redistribution Operation 8-41
Written Exercise: Redistribution and Controlling Routing Update Traffic 8-43
Objectives 8-43
Task 8-43
Completion Criteria 8-44
Policy-Based Routing Using Route Maps 8-45
Verifying Policy-Based Routing 8-58
Summary 8-62
Summary (cont.) 8-63
Review Questions 8-64
Review Questions (cont.) 8-65
CONFIGURING BASIC BGP 9-1
Overview 9-1
Objectives 9-2
BGP Overview 9-4
viii Building Scalable Cisco Internetworking Copyright  2001, Cisco Systems, Inc.

When Not to Use BGP 9-10
BGP Terminology 9-14
BGP Operation 9-38
Written Exercise: BGP Terminology and Operation 9-44
Objectives 9-44
Task 9-44
Completion Criteria 9-45
Configuring BGP 9-46
Verifying BGP 9-57
Summary 9-62
Review Questions 9-64
IMPLEMENTING BGP IN SCALABLE NETWORKS 10-1
Overview 10-1
Objectives 10-2
Objectives (cont.) 10-3
Scalability Problems with IBGP 10-4
Route Reflectors 10-7
Policy Control 10-17
Written Exercise: BGP Route Reflectors and Policy Control 10-28
Objectives 10-28
Task 10-28
Completion Criteria 10-29
Multihoming 10-30
Redistribution with IGPs 10-45
Summary 10-52
Summary (cont.) 10-53
Review Questions 10-54
JOB AIDS AND SUPPLEMENTS A-1
Overview A-1
Extending IP Addresses A-2

Job Aids A-3
IP Addresses and Subnetting A-3
Decimal-to-Binary Conversion Chart A-4
Binary A-4
Supplement 1: Addressing Review A-5
Supplement 2: IP Access Lists A-16
Supplement 3: IP Features A-56
Using IP Unnumbered Interfaces A-56
Using Helper Addresses A-59
Supplement 4: EIGRP A-66
Supplement 5: OSPF A-70
Supplement 6: Route Optimization A-85
Supplement 7: BGP A-109
ROUTER PASSWORD RECOVERY B-1
Overview B-1
Copyright  2001, Cisco Systems, Inc. Building Scalable Cisco Internetworking ix
Router Password Recovery Procedure B-2
ANSWERS C-1
Overview C-1
Chapter 2 Exercises C-2
Answers to Written Exercise: Comparing Routing Protocols C-2
Answers to Review Questions C-3
Chapter 3 Exercises C-4
Answers to Written Exercise: Calculating VLSMs C-4
Answers to Written Exercises: Using Route Summarization C-5
Answers to Review Questions C-5
Chapter 4 Exercises C-6
Answers to Written Exercise: EIGRP Overview C-6
Answers to Review Questions C-7
Chapter 5 Exercises C-8

Answers to Written Exercise: OSPF Operation C-8
Answers to Review Questions C-9
Chapter 6 Exercises C-10
Answers to Written Exercise: OSPF Operation Across Multiple Areas C-10
Answers to Review Questions C-11
Chapter 7 C-13
Answers To Review Questions 13
Answers to Written Exercise: Redistribution and Controlling Routing Update
Traffic C-15
Answers To Review Questions C-16
Chapter 9 Exercises C-18
Answers to Written Exercise: BGP Terminology and Operation C-18
Answers to Review Questions C-19
Chapter 10 Exercises C-21
Answers to Written Exercise: BGP Route Reflectors and Policy Control C-21
Answers to Review Questions C-22
Appendix A Exercises C-23
Answers to Extending IP Addressing Written Exercise: Calculating Subnet
Masks C-23
Answers to IP Access Lists Written Exercise: IP Extended Access Lists C-24
Answers to Review Questions C-24
Laboratory Exercises Written Questions C-25
Laboratory Exercise 1: Configuring EIGRP C-25
Laboratory Exercise 2: Configuring OSPF for a Single Area C-25
Laboratory Exercise 3: Configuring OSPF for a Single Area in an NBMA
Environment C-25
Laboratory Exercise 4: Configuring a Multiarea OSPF Network C-26
Laboratory Exercise 5: Configuring a Multiarea IS-IS Network C-26
Laboratory Exercise 6: Configuring Policy-Based Routing C-26
Laboratory Exercise 7: Configuring Route Redistribution between OSPF and

EIGRP C-27
Laboratory Exercise 8: Configuring BGP C-27
Laboratory Exercise 9: Configuring BGP Route Reflectors and Prefix-List
Filtering C-27
Laboratory Exercise 10: Configuring Multihomed BGP C-27
Laboratory Exercise 12: Super Lab Part I and Part II C-27
LABORATORY EXERCISES D-1
x Building Scalable Cisco Internetworking Copyright  2001, Cisco Systems, Inc.
Introduction D-1
Laboratory Exercise 1: Configuring EIGRP D-2
Objectives D-2
Visual Objective D-3
Command List D-3
Setup D-4
Scenario D-4
Task 1: Enabling EIGRP Within Your Pod D-6
Task 2: Enabling EIGRP Connectivity to the backbone_r1 Router D-7
Completion Criteria D-9
Student Notes D-10
Laboratory Exercise 2: Configuring OSPF for a Single Area D-11
Objectives D-11
Visual Objective D-11
Command List D-12
Setup D-12
Scenario D-12
Task 1: Enabling OSPF Within Your Pod D-13
Task 2: Enabling OSPF Connectivity to the Backbone_r1 Router D-15
Completion Criteria D-16
Student Notes D-17
Laboratory Exercise 3: Configuring OSPF for a Single Area in an NBMA

Environment D-18
Objectives D-18
Visual Objective D-19
Command List D-20
Setup D-20
Scenario D-20
Task 1: Creating the Frame Relay Switch D-21
Task 2: Enabling OSPF Over an NBMA Network Using a Main Interface D-22
Task 3: Enabling OSPF Over an NBMA Network Using a Point-to-Point
Subinterface D-23
Completion Criteria D-23
Student Notes D-24
Laboratory Exercise 4: Configuring a Multiarea OSPF Network D-25
Objectives D-25
Visual Objective D-26
Command List D-27
Setup D-28
Scenario D-29
Task 1: Enabling OSPF with Multiple Areas and Area Summarization D-29
Task 2: Enabling OSPF Stub Area D-31
Task 3: Enabling an OSPF Totally Stubby Area D-31
Task 4: Enabling OSPF Not-So-Stubby Area (Optional) D-32
Task 5: Enabling an OSPF Virtual Link to Support an OSPF Area not
Connected to Area 0 (Optional) D-35
Completion Criteria D-37
Student Notes D-38
Laboratory Exercise 5: Configuring a Multiarea IS-IS Network D-39
Objectives D-39
Visual Objective D-40
Command List D-41

router isis D-41
router isis D-42
Setup D-42
Scenario D-42
Copyright  2001, Cisco Systems, Inc. Building Scalable Cisco Internetworking xi
Task 1: Enabling IS-IS within your pod D-42
Task 2: Enabling connectivity to the backbone_r1 router D-44
Task 3: Changing the IS-IS router type D-44
Task 4: Configure route summarization D-45
Task 5: Using IS-IS show and debug commands D-46
Completion Criteria D-48
Student Notes D-49
Laboratory Exercise 6: Configuring Policy-Based Routing D-50
Objectives D-50
Visual Objective D-50
Command List D-51
Setup D-51
Scenario D-51
Task 1: Enable IP Policy-Based Routing at pxr1 D-52
Completion Criteria D-54
Student Notes D-55
Laboratory Exercise 7: Configuring Route Redistribution Between OSPF and
EIGRP D-56
Objectives D-56
Visual Objective D-56
Command List D-57
Setup D-57
Scenario D-57
Task 1: Enabling OSPF Between pxr1 (S0 and S1)
and pxr2 (S0 and S1) D-58

Task 2: Enabling EIGRP Between pxr1 (S2) and pxr3 (S0) D-58
Task 3: Enabling Route Redistribution Between OSPF and EIGRP D-58
Task 4: Enabling Route Redistribution from EIGRP
to OSPF with Filtering D-59
Completion Criteria D-60
Student Notes D-61
Laboratory Exercise 8: Configuring BGP D-62
Objectives D-62
Visual Objective D-63
Command List D-63
Setup D-65
Scenario D-65
Task 1: Enabling EBGP D-66
Task 2: Enabling Full-Mesh IBGP Within Your Pod (AS) D-68
Completion Criteria D-70
Student Notes D-71
Laboratory Exercise 9: Configuring BGP Route Reflectors and Prefix-List
Filtering D-72
Objectives D-72
Visual Objective D-72
Command List D-73
Setup D-73
Scenario D-73
Task 1: Enabling pxr1 to be the Route Reflector D-74
Task 2: Enabling Inbound Prefix-List D-76
Completion Criteria D-76
Student Notes D-77
Laboratory Exercise 10: Configuring Multi-homed BGP D-78
Objectives D-78
Visual Objective D-79

Command List D-79
xii Building Scalable Cisco Internetworking Copyright  2001, Cisco Systems, Inc.
Setup D-80
Scenario D-80
Task 1: Enabling a Second EBGP Connection D-81
Completion Criteria D-83
Laboratory Exercise 11: Super Lab I D-85
Part I D-85
Objectives D-85
Visual Objective D-86
Command List D-86
Setup D-86
Scenario D-86
Task D-88
Completion Criteria D-88
Student Notes D-89
Laboratory Exercise 12: Super Lab II D-90
Part II D-91
Objectives D-92
Visual Objective D-92
Command List D-92
Setup D-92
Scenario D-92
Task D-94
Completion Criteria D-94
Student Notes D-95

7 1
Configuring IS-IS Protocol 2
Overview 3
This lesson provides an overview of Intermediate System-to-Intermediate System (IS-IS) 4
technology, and its structures and protocols, as well as basic configuration examples. The lesson 5
begins with Open System Interconnection (OSI) routing and then focuses on Integrated IS-IS as 6
a version that supports IP networks. Basic IS-IS and Integrated IS-IS router configuration 7
commands, examples, and some troubleshooting guidelines are presented at the end of the 8
lesson. The major part of this lesson is dedicated to an explanation of IS-IS concepts and 9
capabilities, including hierarchy and addressing of OSI-based networks. 10
Outline 11
The lesson includes these sections: 12
n Objectives 13
n Introduction to OSI Protocols and IS-IS Routing 14
n Operation of IS-IS 15

n IP and OSI Routing with Integrated IS-IS 16
n Basic Integrated IS-IS Router Configuration 17
n Modeling WAN Networks in Integrated IS-IS 18
n Summary 19
n Review Questions 20
Click Here to Post Review Comments
7-2 Building Scalable Cisco Internetworks (BSCI) v1.2 Copyright  2001, Cisco Systems, Inc.
Objectives 21
This section lists the lesson objectives. 22
Insert Slide here.
n Explain basic OSI terminology and network layer protocols used in OSI 23
n Identify similarities and differences between Integrated IS-IS and OSPF 24
n Identify characteristics of an effective addressing plan for IS-IS deployment 25
n Explain how networks and interfaces are represented in IS-IS 26
n List the types of IS-IS routers and their role in IS-IS area design 27
n Describe the hierarchical structure of IS-IS areas 28
© 2001, Cisco Systems, Inc. BSCI v1.2 — 7-2
ObjectivesObjectives
Upon completing this lesson, you will be able to:
• Explain basic OSI terminology and network layer
protocols used in OSI
• Identify similarities and differences between
Integrated IS-IS and OSPF
• Identify characteristics of an effective addressing
plan for IS-IS deployment
• Explain how networks and interfaces are
represented in IS-IS
• List the types of IS-IS routers and their role in IS-IS
area design
• Describe the hierarchical structure of IS-IS areas

Copyright  2001, Cisco Systems, Inc. Configuring IS-IS Protocol 7-3
Objectives (cont.) 29
Insert Slide here.
n Describe the concept of establishing adjacencies 30
n Describe the concepts of routing traffic transport and database synchronization 31
n Explain the basic principles of area routing 32
n Explain IS-IS nonbroadcast multiaccess (NBMA) network modeling solutions in switched 33
WAN networks 34
n Identify the steps to configure Cisco routers for proper Integrated IS-IS operation, given an 35
addressing scheme and other laboratory parameters 36
n Identify verification methods that ensure proper operation of Integrated IS-IS on Cisco 37
routers 38
© 2001, Cisco Systems, Inc. BSCI v1.2 — 7-3
Objectives (cont.)
Objectives (cont.)
• Describe the concept of establishing adjacencies
• Describe the concepts of routing traffic transport and
database synchronization
• Explain the basic principles of area routing
• Explain IS-IS NBMA (non-broadcast multi-access
network) modeling solutions in switched WAN
networks
• Given an addressing scheme and other laboratory
parameters, identify the steps to configure Cisco
routers for proper Integrated IS-IS operation
• Identify verification methods which ensure proper
operation of Integrated IS-IS on Cisco routers
7-4 Building Scalable Cisco Internetworks (BSCI) v1.2 Copyright  2001, Cisco Systems, Inc.
Introduction to OSI Protocols and IS-IS 39
Routing 40

Insert Slide here.
The OSI protocols are part of an international program to develop data-networking protocols 41
and other standards that facilitate multivendor equipment interoperability. The OSI program 42
grew out of a need for international networking standards and is designed to facilitate 43
communication between hardware and software systems despite differences in underlying 44
architectures. 45
The OSI specifications were conceived and implemented by two international standards 46
organizations: the International Organization for Standardization (ISO) and the International 47
Telecommunication Union Telecommunication Standardization Sector (ITU-T). 48
The world of OSI internetworking includes various network services with these characteristics: 49
n Independence of underlying communications infrastructure 50
n End-to-end transfer 51
n Transparency 52
n Quality of service (QoS) selection 53
n Addressing 54
© 2001, Cisco Systems, Inc. BSCI v1.2 — 7-5
OSI Protocols
OSI Protocols
ISO and OSI?
• The International Organization for
Standardization (ISO) has been constituted to
develop standards for data networking.
• The Open System Interconnection (OSI)
protocols represent an international
standardization program that facilitates
multivendor equipment interoperability.
Copyright  2001, Cisco Systems, Inc. Configuring IS-IS Protocol 7-5
Insert Slide here.
The OSI protocol suite supports numerous standard protocols at the physical, data-link, network, 55
transport session, presentation, and application layers. 56

OSI network-layer addressing is implemented by using two types of hierarchical addresses: 57
network service access point (NSAP) addresses and network-entity titles. An NSAP is a 58
conceptual point on the boundary between the network and the transport layers. The NSAP is 59
the location at which OSI network services are provided to the transport layer. Each transport-60
layer entity is assigned a single NSAP, which is individually addressed in an OSI internetwork 61
using NSAP addresses. 62
The OSI protocol suite specifies two routing protocols at the network layer: End System-to-63
Intermediate System (ES-IS) and Intermediate System-to-Intermediate System (IS-IS). In 64
addition, the OSI suite implements two types of network services: connectionless service and 65
connection-oriented service. 66
© 2001, Cisco Systems, Inc. BSCI v1.2 — 7-6
OSI Protocols (cont.)OSI Protocols (cont.)
The OSI protocol suite supports:
• Numerous standard protocols at each layer of
the OSI reference model
• OSI network-layer
hierarchical addressing
• Two routing protocols at the
network layer
7-6 Building Scalable Cisco Internetworks (BSCI) v1.2 Copyright  2001, Cisco Systems, Inc.
Insert Slide here.
In an OSI network four significant architectural entities exist: hosts, areas, a backbone, and a 67
domain. A domain is any portion of an OSI network that is under a common administrative 68
authority. Within any OSI domain, one or more areas can be defined. An area is a logical entity; 69
it is formed by a set of contiguous routers and the data links that connect them. All routers in 70
the same area exchange information about all the hosts that they can reach. The areas are 71
connected to form a backbone. All routers on the backbone know how to reach all areas. The 72
term “end system” (ES) refers to any nonrouting host or node; “intermediate system” (IS) 73
refers to a router. These terms are the basis for the OSI ES-IS and IS-IS protocols. 74
© 2001, Cisco Systems, Inc. BSCI v1.2 — 7-7

OSI Protocols—
Terminology
OSI Protocols—
Terminology
Terminology used in OSI
• End system (ES) is any nonrouting
network nodes (host)
• Intermediate system (IS) is a router
• An area is a logical entity
–Formed by a set of contiguous routers,
hosts, and the data links that connect them
• Domain is a collection of connected areas
Copyright  2001, Cisco Systems, Inc. Configuring IS-IS Protocol 7-7
Insert Slide here.
The OSI protocol suite supports numerous standard protocols at each of the seven OSI layers. 75
The figure here illustrates the entire OSI protocol suite and its relation to the layers of the OSI 76
reference model. 77
© 2001, Cisco Systems, Inc. BSCI v1.2 — 7-8
OSI Protocol Suiteand its Mapping to the
OSI Reference Model
OSI Protocol Suite and its Mapping to the
OSI Reference Model
7-8 Building Scalable Cisco Internetworks (BSCI) v1.2 Copyright  2001, Cisco Systems, Inc.
Insert Slide here.
Connectionless Network Service (CLNS) uses a datagram data transfer service and does not 78
require a circuit to be established before data is transmitted. In contrast, Connection-Mode 79
Network Service (CMNS) requires a circuit to be established before transmitting data. While 80
CLNS and CMNS define the actual services provided to the OSI transport layer entities that 81
operate immediately above the network layer, Connectionless Network Protocol (CLNP) and 82
Connection-Oriented Network Protocol (CONP) name the protocols that these services use to 83

convey data at the network layer. CLNP is the OSI equivalent of IP. 84
© 2001, Cisco Systems, Inc. BSCI v1.2 — 7-9
OSI Network Services—
What to Route in OSI Environment?
OSI Network Services—
What to Route in OSI Environment?
Two types of OSI network-layer services
are available to the OSI transport layer:
• Connectionless Network Service (CLNS)
–CLNS performs datagram transport
• Connection-Mode Network Service (CMNS)
–CMNS requires explicit establishment
of paths between communicating transport-
layer entities
Copyright  2001, Cisco Systems, Inc. Configuring IS-IS Protocol 7-9
Insert Slide here.
CONP is based on the X.25 Packet-Layer Protocol (PLP) and is described in the ISO 8208 85
standard “X.25 Packet-Layer Protocol for DTE.” 86
CONP provides the interface between CMNS and upper layers. It is a network-layer service 87
that acts as the interface between the transport layer and CMNS and is described in the ISO 88
8878 standard. CMNS functions include connection setup, maintenance, and termination; it also 89
provides a mechanism for requesting a specific QoS. 90
© 2001, Cisco Systems, Inc. BSCI v1.2— 7-10
OSI Network Services—
Connection-Oriented Mode
OSI Network Services—
Connection-Oriented Mode
CMNS/CONP:
• CONP is an OSI network-layer protocol that
carries upper-layer data and error indications

over connection-oriented links
• CMNS performs functions related to the
explicit establishment of paths via CONP
• When support is provided for CMNS, the
routing uses the X.25 protocols as the
relaying functions
7-10 Building Scalable Cisco Internetworks (BSCI) v1.2 Copyright  2001, Cisco Systems, Inc.
Insert Slide here.
CLNP is an OSI network-layer protocol that carries upper-layer data and error indications over 91
connectionless links. CLNP provides the interface between CLNS and upper layers. CLNS 92
does not perform connection setup or termination because paths are determined independently 93
for each packet that is transmitted through a network. In addition, CLNS provides best-effort 94
delivery, which means that no guarantee exists that data will not be lost, corrupted, misordered, 95
or duplicated. CLNS relies on transport-layer protocols to perform error detection and 96
correction. 97
© 2001, Cisco Systems, Inc. BSCI v1.2— 7-11
OSI Network Services—
Connectionless Mode
OSI Network Services—
Connectionless Mode
CLNP/CLNS:
• CLNP is an OSI network-layer protocol that
carries upper-layer data and error indications
over connectionless links
• CLNS provides network-layer services to the
transport layer via CLNP
• When support is provided for CLNS, the
routing uses routing protocols to exchange
routing information
Copyright  2001, Cisco Systems, Inc. Configuring IS-IS Protocol 7-11

Insert Slide here.
The OSI protocol suite includes several routing protocols and one router discovery protocol (ES-98
IS, an analog to Address Resolution Protocol [ARP] in IP). Although not explicitly a routing 99
protocol, ES-IS is included in this lesson because it is commonly used with routing protocols to 100
provide end-to-end data movement through an internetwork. 101
To simplify router design and operation, OSI distinguishes between level-1, level-2, and level-3 102
routing. Level-1 ISs communicate with other level-1 ISs in the same area. Level-2 ISs route 103
between level-1 areas and form an intradomain routing backbone. Level-3 routing is done 104
between separate domains. 105
Hierarchical routing simplifies backbone design, because level-1 ISs only need to know how to 106
get to the nearest level-2 IS. 107
© 2001, Cisco Systems, Inc. BSCI v1.2— 7-12
OSI Network Services—Routing
Protocols
OSI Network Services—Routing
Protocols
ISO has developed standards for two
types of protocols:
• ES-IS dicovery protocols: “routing” between
End Systems and Intermediate Systems
referred as level-0 “routing”
• IS-IS routing protocols: hierarchical
(level-1, level-2 and level-3) routing between
Intermediate Systems
7-12 Building Scalable Cisco Internetworks (BSCI) v1.2 Copyright  2001, Cisco Systems, Inc.
Insert Slide here.
Each ES lives in a particular area. OSI routing begins when the ESs discover the nearest IS by 108
listening to Intermediate System Hello (ISH) packets. When an ES wants to send a packet to 109
another ES, it sends the packet to one of the ISs on its directly attached network (level-0 110
routing). The router then looks up the destination address and forwards the packet along the 111

best route. If the destination ES is on the same subnetwork, the local IS will know this from 112
listening to End System Hello (ESH) packets and will forward the packet appropriately. The IS 113
also might provide a redirect message back to the source to tell it that a more direct route is 114
available. 115
If the destination address is an ES on another subnetwork in the same area, the IS will know the 116
correct route (level-1 routing) and will forward the packet appropriately. 117
If the destination address is an ES in another area, the level-1 IS sends the packet to the nearest 118
level-2 IS (level-2 routing). Forwarding through level-2 ISs continues until the packet reaches a 119
level-2 IS in the destination area. Within the destination area, ISs forward the packet along the 120
best path until the destination ES is reached. 121
Routing between separate domains is referred to as level-3 routing. 122
© 2001, Cisco Systems, Inc. BSCI v1.2— 7-13
OSI Network Services—OSI Routing
in Operation
OSI Network Services—OSI Routing
in Operation
Area-1
Area-2
IS
IS
IS IS
ESES
Domain
Level-0 routing between ESs and
ISs on the same subnet
Level-0 routing between ESs and
ISs on the same subnet
Level-1 routing between ISs
within the same area
Level-1 routing between ISs

within the same area
Level-2 routing between different
areas within the same domain
Level-2 routing between different
areas within the same domain
Level-3 routing between separate domains
Level-3 routing between separate domains
Copyright  2001, Cisco Systems, Inc. Configuring IS-IS Protocol 7-13
Insert Slide here.
For routing in the ISO CLNS/CLNP environment, Cisco routers support these protocols: 123
n IS-IS: Routers usually operate as ISs and can exchange reachability information with other 124
ISs using the IS-IS protocol. As an IS, a Cisco router can operate at level 1 only, at level 2 125
only, or at both levels. In the last case, the router can advertise itself at level 1 as an exit 126
point from the area. Integrated IS-IS allows the IS-IS protocol to propagate routing 127
information for other protocols as well as, or instead of, CLNS. Specifically, IS-IS can route 128
CLNS, IP, or both (“dual” mode). 129
n ISO-IGRP: Cisco routers have available a proprietary routing protocol for CLNS. ISO-130
IGRP is, as its name suggests, based on Cisco’s Interior Gateway Routing Protocol (IGRP). 131
It uses distance vector technology to propagate routing information. As such, it shares some 132
of the limitations of its IP counterpart, including long convergence times (due to periodic 133
updates and long invalid-times and holdtimes). 134
n Static CLNS routes: As with IP, static CLNS routes can be created. 135
© 2001, Cisco Systems, Inc. BSCI v1.2— 7-14
OSI Network Services—IS-IS RoutingOSI Network Services—IS-IS Routing
Intermediate System to Intermediate
System (IS-IS) is a dynamic link-state
routing protocol in ISO CLNS environment
for routing CLNP
• Link-state routing protocol in the OSI stack
Alternative to IS-IS protocols is deploying

CISCO ISO-IGRP or static routing