Juniper网络学习指南：JNCIA认证详解

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"《Juniper网络认证互联网关联者（JNCIA）学习指南》是由Joseph M. Soricelli、John L. Hammond、Galina Diker Pildush、Thomas E. VanMeter和Todd M. Warble共同编著的，最初由Juniper Networks Inc.与Sybex Inc.合作开发。这本书是为了满足初学者对Juniper设备学习的需求，尤其适合那些希望获取JNCIA认证的人。由于原版纸质书籍（ISBN:0-7821-4071-8）已停止印刷，电子版提供了方便获取。本书的内容包括但不限于以下几个部分： 1. **路由器组件**：介绍了Juniper路由器的基本组成部分，帮助读者理解网络设备内部结构及其功能。 2. **接口**：详细讲解了Juniper路由器的接口配置和管理，包括物理接口、逻辑接口以及它们在路由和数据传输中的作用。 3. **协议独立路由**：这部分涵盖了路由协议的原理和实现，让读者掌握如何在不依赖特定路由协议的情况下进行路由决策。 4. **路由策略**：深入解析路由策略的创建和应用，包括访问控制列表（ACL）、前缀列表和策略路由，以优化网络流量控制。 5. **路由信息**：探讨路由表的构成和维护，以及如何通过路由协议如BGP、OSPF等动态调整路由信息。虽然电子版已经去除了原出版商的痕迹，但请注意，尽管本书可能有助于考生准备JNCIA考试，但 Juniper Networks Inc.并不保证阅读此书就能确保考试通过。因此，这本书应作为学习材料，结合实践和官方文档来全面提升对Juniper网络技术的理解。版权方面，所有2003年至2006年的权利都归Juniper Networks Inc.所有。在使用时，请尊重版权规定，仅限于个人学习目的。如需购买或查询原版纸质书，请联系John Wiley & Sons出版社，可通过其网站www.wiley.com获取更多信息。"

Introduction

xvi

JNTCP Nondisclosure Agreement

Juniper Networks considers all written and practical JNTCP exam material to be confidential

intellectual property. As such, an individual is not permitted to take home, copy, or re-create the

entire exam or any portions thereof. It is expected that candidates who participate in the JNTCP

will not reveal the detailed content of the exams.

For written exams delivered at Prometric testing centers, candidates must accept the online

agreement before proceeding with the exam. When taking practical exams, candidates are pro-

vided with a hard-copy agreement to read and sign before attempting the exam. In either case,

the agreement can be downloaded from the JNTCP website for your review prior to the testing

date. Juniper Networks retains all signed hard-copy nondisclosure agreements on file.

Candidates must accept the online JNTCP Online Agreement in order for their

certifications to become effective and to have a certification number assigned.

You can do this by going to the CertManager site at

http://www.certmanager

.net/juniper

Resources for JNTCP Participants

Reading this book is a fantastic place to begin preparing for your next JNTCP exam. You

should supplement the study of this volume’s content with related information from various

sources. The following resources are available for free and are recommended to anyone seeking

to attain or maintain Juniper Networks certified status.

JNTCP Website

The JNTCP website (

http://www.juniper.net/certification

) is the place to go for the

most up-to-date information about the program. As the program evolves, this website is peri-

odically updated with the latest news and major announcements. Possible changes include new

exams and certifications, modifications to the existing certification and recertification require-

ments, and information about new resources and exam objectives.

The site consists of separate sections for each of the certification tracks. The information

you’ll find there includes the exam number, passing scores, exam time limits, and exam topics.

A special section dedicated to resources is also provided to supply you with detailed exam topic

outlines, sample written exams, and study guides. The additional resources listed next are also

linked from the JNTCP website.

CertManager

The CertManager system (

http://www.certmanager.net/juniper

) provides you with a

place to track your certification progress. The site requires a username and password for access,

and you typically use the information contained on your hard-copy score report from Prometric

the first time you log in. Alternatively, a valid login can be obtained by sending an e-mail mes-

sage to

certification@juniper.net

with the word

certmanager

in the subject field.

xvii

Introduction

Once you log in, you can view a report of all your attempted exams. This report includes the

exam dates, your scores, and a progress report indicating the additional steps required to attain

a given certification or recertification. This website is where you accept the online JNTCP agree-

ment, which is a required step to become certified at any level in the program. You can also use

the website to request the JNTCP official certification logos to use on your business cards,

resumes, and websites.

Perhaps most important, the CertManager website is where all your contact information is

kept up-to-date. Juniper Networks uses this information to send you certification benefits, such

as your certificate of completion, and to inform you of important developments regarding your

certification status. A valid company name is used to verify a partner’s compliance with certi-

fication requirements. To avoid missing out on important benefits and information, you should

ensure your contact information is kept current.

Juniper Networks Training Courses

Juniper Networks training courses (

http://www.juniper.net/training

) are the best source

of knowledge for seeking a certification and to increase your hands-on proficiency with Juniper

Networks equipment and technologies. While attendance of official Juniper Networks training

courses doesn’t guarantee a passing score on the certification exam, it does increase the likelihood

of your successfully passing it. This is especially true when you seek to attain JNCIP or JNCIE sta-

tus, where hands-on experience is a vital aspect of your study plan.

Juniper Networks Technical Documentation

You should be intimately familiar with the Juniper Networks technical documentation set

(

http://www.juniper.net/techpubs). During the JNTCP lab exams (JNCIP and JNCIE),

these documents are provided in PDF on your PC. Knowing the content, organizational struc-

ture, and search capabilities of these manuals is a key component for a successful exam attempt.

At the time of this writing, hard-copy versions of the manuals are provided only for the hands-

on lab exams. All written exams delivered at Prometric testing centers are closed-book exams.

Juniper Networks Solutions and Technology

To broaden and deepen your knowledge of Juniper Networks products and their applications,

you can visit http:///www.juniper.net/techcenter. This website contains white papers,

application notes, frequently asked questions (FAQ), and other informative documents, such as

customer profiles and independent test results.

Group Study

The Groupstudy mailing list and website (http://www.groupstudy.com/list/juniper.html)

is dedicated to the discussion of Juniper Networks products and technologies for the purpose of

preparing for certification testing. You can post and receive answers to your own technical ques-

tions or simply read the questions and answers of other list members.

Introduction

xviii

JNCIA Study Guide

Now that you know a lot about the JNTCP, we need to provide some more information about this

text. We begin with a look at some topics and information you should already be familiar with

and then examine what topics are in the book. Finally, we discuss how to utilize this resource and

the accompanying CD.

What You Should Know Before Starting

If you are familiar with networking books, you might be a little surprised by the starting topic

in Chapter 1. It is not the Open Systems Interconnection (OSI) model common to books in our

industry, but instead the software that operates the router. In the following chapters, we dive

headfirst into the details of running a network using the JUNOS software. This philosophy of

knowing the basics is quite ingrained in the Juniper Networks Education courseware and cer-

tification exams, so we follow that assumption.

Tips for Taking Your Exam

Many questions on the exam have answer choices that at first glance look identical. Remember

to read through all the choices carefully because “close” doesn’t cut it. Although there is never

any intent on the part of Juniper Networks to trick you, some questions require you to think

carefully before answering. Also, never forget that the right answer is the best answer. In some

cases, you may feel that more than one appropriate answer is presented, but the best answer

is the correct answer.

Here are some general tips for exam success:



Arrive early at the exam center, so you can relax and review your study materials.



Read the questions carefully. Don’t just jump to conclusions. Make sure that you’re clear

about exactly what each question asks.



Don’t leave any questions unanswered. They count against you.



When answering multiple-choice questions that you’re not sure about, use a process of

elimination to eliminate the obviously incorrect answers first. Doing this greatly improves

your odds if you need to make an educated guess.



Mark questions that you’re not sure about. If you have time at the end, you can review

those marked questions to see if the correct answer “jumps out” at you.

After you complete the exam, you’ll get immediate, online notification of your pass or fail sta-

tus, a printed Examination Score Report that indicates your pass or fail status, and your exam

results by section. (The test administrator will give you the printed score report.) Test scores

are automatically forwarded to Juniper Networks within five working days after you take the

test, so you don’t need to send your score to them.

xix

Introduction

This means that you should be knowledgeable and conversant in the following topics:

OSI Model The OSI model defines seven different OSI layers—Physical, Data Link, Network,

Transport, Session, Presentation, and Application. This model allows vendors and engineers to

develop products designed for a specific OSI level. The segmentation this provides splits the

overall “problem” of networking into smaller, more manageable pieces. Each layer of the model

has certain responsibilities assigned to it and interacts with its neighboring levels in a predefined

manner.

Switches Ethernet, Asynchronous Transfer Mode (ATM), and Frame Relay switches all oper-

ate at the Data Link layer (Layer 2) of the OSI model. You should understand the concept of a

logical address and know how the local significance of those addresses plays a part in the scal-

ability of the network.

Routers Routers operate at the Network layer (Layer 3) of the OSI model. They connect sep-

arate IP subnets together and route packets across a network in a hop-by-hop manner.

Ethernet Networks Ethernet networks are commonly referred to as a broadcast domain. This

means that all connected hosts receive all transmissions on the physical media. Each host uses

the destination Media Access Control (MAC) address of the Ethernet frame to determine which

frame it should process. The MAC addresses on a segment are learned through the Address Res-

olution Protocol (ARP).

Point-to-Point Links Point-to-point links in a network are often referred to as wide area net-

work (WAN) links. This generalized term is used to describe the nature of a point-to-point link—

it contains no end IP hosts. In a core network, point-to-point links connect two network devices.

These devices can be ATM switches, Frame Relay switches, or network routers. These network

links have the ability to use one of many Layer 2 encapsulations, including ATM, Frame Relay,

the Point-to-Point Protocol (PPP), and High-Level Data Link Control (HDLC).

IP Addressing and Subnetting IP hosts and routers use a common packet format for all data

transmissions. This includes the destination and source IP address fields, which use a 32-bit

address space. Humans often use a dotted decimal format to represent an IP address. The address

contains a host portion and a network portion. For example, 192.168.1.1 /24 defines a network

address of 192.168.1.0 and a host address of 1 on that subnet.

TCP The Transmission Control Protocol (TCP) operates at the Transport layer (Layer 4) of the

OSI model. It defines a common header format, which includes destination and source port num-

bers. TCP provides a connection-oriented session between two end hosts that is established using

a three-way handshake. TCP also uses a sliding window for flow control between the hosts.

UDP The User Datagram Protocol (UDP) also operates at the Transport layer (Layer 4) of the

OSI model. Like TCP, it defines a common header format and uses destination and source port

numbers. Unlike TCP, however, UDP provides a connectionless session between two end hosts

that resembles a flowing packet stream. No reliability or flow control is provided to the hosts.

ICMP The Internet Control Message Protocol (ICMP) uses the IP packet format to perform

its functions. Therefore, we often describe it as operating at the Network layer of the OSI model.

Introduction

The main function of ICMP is to generate error messages that should be acted upon by network

devices.

Network Troubleshooting Network engineers use ping, a function of ICMP, to verify connec-

tivity in the network. Should a problem be found, a second useful tool is traceroute. Traceroute

sends UDP messages in a hop-by-hop fashion and provides you with the exact route, and pos-

sible trouble spot, through your network.

If you feel that you need a refresher on these topics, please visit the Core Routing website

listed in the “About the Authors and Technical Editors” section later in this introduction. You

will find resources there that you may use to complete your knowledge base.

Scope of the Book

While it’s easy to say that the book covers the objectives for the JNCIA-M exam, we anticipate

that this book, like the exam itself, is only the beginning of your reading and learning about

Juniper Networks products and the JUNOS software. To that end, we tried to begin each chap-

ter with some basic theory concepts. In addition, the foundation for future learning is laid out

in the protocol packet formats and detailed explanations of what they include. From there, we

begin to explore the implementation details of the JUNOS software in relation to the chapter

subject.

All router output in the book was taken from JUNOS software versions 5.4

and 5.5.

To truly cover all there is to know about the JUNOS software and the Juniper Networks

routers would take quite a few books. We currently have plans for writing only a few that relate,

like this book, to the certification program. Therefore, you will notice a difference in the depth

(or lack thereof) of detail from chapter to chapter. The material in some chapters is enough to

satisfy your requirements for almost all of your certification needs, but is only the tip of the ice-

berg within that subject matter. In those cases, we discuss all we need and leave the rest to your

own reading from other sources. Other topics, like routing protocols, require a deep under-

standing at all levels of the certification program. Those topics, in this book, are truly the basic

concepts. We leave the rest of the knowledge needed to the forthcoming books in the series.

In the end, we hope that you get enough data to perform well on the JNCIA-M exam, but

that you are left longing for more detailed and advanced information. That’s a good sign; it is

the mark of a great network engineer. Please know that additional resources are available to you

and that more Sybex Study Guides are on the way to quench your thirst for knowledge.

What Does This Book Cover?

This book covers everything you need to know to pass the JNCIA-M exam. It teaches you how

to configure and operate many protocols and features of the JUNOS software. While this material

is helpful, we also recommend gaining some hands-on practice. We understand that accessing a

live Juniper Networks router in a lab environment is difficult, but if you can manage it you’ll retain

this knowledge far longer in your career.

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