OReilly JUNOS enterprise routing a practical guide to JUNOS software and enterprise certification mar 2008 ISBN 0596514425

JUNOS Enterprise Routing covers all three certification exams in this track: Juniper Networks Certified Internet Associate JNCIA-ERJuniper Networks Certified Internet Specialist JNCIS-ER

by Doug Marschke; Harry Reynolds

Publisher: O'Reilly Pub Date: March 27, 2008 Print ISBN-13: 978-0-596-51442-6 Pages: 812

Enhanced Services (ES) This book is the official study guide forall three Juniper Enterprise Routing certification exams, and ishighly recommended reading to pass the exams With its field-guide emphasis on practical solutions, you can easily take thebook beyond the classroom and into working networks as adesign, maintenance, and troubleshooting reference par

excellence JUNOS Enterprise Routing covers all three

certification exams in this track:

Juniper Networks Certified Internet Associate (JNCIA-ER)Juniper Networks Certified Internet Specialist (JNCIS-ER)Juniper Networks Certified Internet Expert (JNCIE-ER)

With more services such as voice, conference, and multicast onthe IP router platform, the market for enterprise routers is

growing exponentially, and the need for certified engineers tokeep up with network developments in protocols and security isparamount For everyone who works with Juniper enterpriseand edge routing environments, this is a must-have book

Section 9.4 DiffServ CoS Deployment and Verification

Section 9.5 J-Series Adaptive Shapers and Virtual ChannelsSection 9.6 Conclusion

most titles (safari.oreilly.com) For more information, contactour corporate/institutional sales department: (800) 998-9938 orcorporate@oreilly.com

This book uses RepKover™, a durable and flexible lay-flat

binding

ISBN: 978-0-596-51442-6

[M]

In 1998, Juniper Networks launched its first product, the M40router, and in doing so sparked a period of innovation in IP

routing that continues to accelerate Although the M40 was

designed to carry Internet traffic for Internet service providers(ISPs), the benefits of IP networking were becoming apparent

intelligent policies to replace large amounts of basic

configuration, which gives the engineer a brilliantly practicalway to deploy services beyond simple routing JUNOS

represents the most valuable contribution to networking thatJuniper has made: it's reliable, flexible, secure, and simple touse, and an increasing numbers of businesses are finding thatthese qualities are compelling enough to move to Juniper andaway from legacy "first-generation" routers and their less

capable operating systems

P2.1 Why Enterprise Routing?

Many books have been written about JUNOS, but this book isunique in that it will prepare you to use JUNOS in an enterprise-

centric sense Enterprise is a term that equipment

manufacturers and others use to distinguish the internal

networks of "normal" businesses from the typically larger onesrun by service providers, phone companies, and other networkproviders Although there are, of course, similarities, every type

of business requires its own unique set of capabilities from itsnetwork infrastructure regardless of its size: financial

institutions have different needs from those of retail chains,which themselves differ from governments and universities

provider networks Although some aspects of networking

technology—such as faster interfaces and greater degrees ofreliability—continue to be attributes of both environments, theirdesign goals and operational techniques differ greatly A service

There are signs that this attitude is changing Companies invirtually every industry have embraced the idea that more

effective use of their IT infrastructure can make them morecompetitive and efficient To that end, enterprise executives areincreasingly interested in innovative ways to capitalize on theirinvestments in data networks This trend is most pronounced indata-intensive industries such as banking, finance, and

insurance, but it extends into even less obvious areas such asmanufacturing and transportation

Service provider and enterprise networks continue to be

different in terms of their customer base and their relationship

to technology, but networking in general is becoming

increasingly important to the competitiveness of all types ofcompanies Some of the most outstanding examples of the

ways that networking can improve business fundamentals arethose related to developments in IP routing, and many of thosedevelopments have recently come from Juniper Networks

P2.2 Why Is Routing So Important?

Routing is the hub around which all of IP connectivity revolves

At the simplest level, routing establishes basic internetwork

uniquely identifies each device, and organizes individual devicesinto a hierarchical network structure Traditionally, routers havealso served as the media adapters that have connected remoteoffices to the headquarters via a WAN The most recent trend,though, is to see routers as the integration platforms for a widevariety of network enhancements such as security, policy, andservices that extend the capabilities of IP to support telephony,video, legacy service integration, and other applications over aconverged network

This means the router has become the primary control point inthe increasingly complex network environment, holding

responsibility for service quality and security, monitoring andefficiency, and other attributes that allow networks to add

value If you control the routers, you control the network This

is true in a static network, of course, but even more so in

today's typical case of a rapidly evolving enterprise, where

migration to fully IP-based services is underway This book willshow you how you can use Juniper routers to ease this

migration and arrive at a more successful outcome with lesswork than other platforms would require This is important

because although the basics of routing remain somewhat thesame, the more advanced aspects are under constant

development, and the authors have done a great job of showingyou how to address the continually changing enterprise networkenvironment

Juniper has long understood that constant change is a fact oftoday's networks, and has worked to bring new levels of

performance, dependability, and scalability to routing platformsand the software that runs them CIOs and IT departments

realize that by deploying a more powerful, flexible tool at theirnetworks' control points, they enable their networks to addressnew challenges more easily and economically, and that's thebest way to support the competitiveness of their company

P2.3 How This Book Will Help You

telecommunications with outstanding work for Juniper and SNT.Both have extensive experience in training and certification, andboth are established authors of educational materials, courseguides, and books that have helped thousands of networkingengineers obtain knowledge to set them apart from the

competitive field Their students and readers have gone on toform an elite group

This book will serve two purposes for you First, it will allow you

to quickly acquire the knowledge to succeed in implementingenterprise networks, no matter how advanced, with Juniper

Networks routers Second, it will help you to prove your

knowledge by passing the Juniper Networks Certified InternetExpert (JNCIE-ER) examination, one of the most highly

regarded certifications in the industry Each chapter's tutorialtrains you in the most essential elements of the subject, andthe review questions at the end of each chapter allow you toconfirm the knowledge you've acquired Doug and Harry haveextensive experience in both the practical and the pedagogicalcomponents of this mission, and this book is an excellent

example of how theory and practice can come together in onecomprehensive yet concise package

Juniper Networks routers and the JUNOS operating system arechanging the way IT departments are regarding their IP

networks, allowing them to put greater trust in the capabilities

of their routing infrastructures and thereby deliver much

greater value to the bottom lines of their organizations Withthis book, Doug and Harry have delivered the tools necessaryfor every network engineer to add valuable knowledge and skills

to his professional portfolio, and to help his company reap thebenefits of the enterprise IP revolution All that's required is foryou to accept the challenge!

—Matt Kolon

Hong Kong, January 2008

He is JNCIP #119-certified and holds a JNCIA-FW, JNCIA-WX,and various other industry certifications Prior to joining JuniperNetworks, Mario served in the U.S Army and worked at

Metrolink, Duro Communications, and Solunet Inc He is

married to his best friend of 12 years, Stacy

Jack W Parks has more than 15 years of experience in IT and

has worked in almost every position known in the realm of IT.Most recently, he has focused on enterprise routing and

switching, service provider routing, and MPLS and VPNs Jackholds a BS in business information systems from John BrownUniversity and has received several industry certifications,

including CCI #11685, JNCIS-M, JNCIA-SSL, and JNCIA-FWV.After serving eight years in the U.S Air Force, Jack transitionedinto the corporate world working for service providers in theenterprise and ISP market spaces Jack is currently a Junipersystems engineer based in Atlanta

The world of enterprise routing with Juniper Networks devices isgetting very exciting—new technologies, products, and networkdevelopments are making the enterprise network environmentone of the most dynamic places to be However, we, the

authors, hope to focus that energy by providing you with a

detailed and practical foundation that ensures effective use ofJUNOS software in your day-to-day job

Because we are also involved in the development and testing ofcertification exams, including those for enterprise routing, thisbook does double duty It is both a field guide and a certificationstudy guide Readers who are interested in attaining a JuniperNetworks certification level are wise to note that we discuss andcover topics that are relevant to the official exams (hint, hint),and the end of each chapter provides a listing of examinationtopics covered as well as a series of review questions that allowyou to test your comprehension

Regardless of one's certification plans, this one-of-a-kind bookwill not be obsolete just because you pass an exam In fact, wewrote this material to serve as a field guide to be useful almostanytime you log on to a Juniper Networks router The extensiveuse of tutorials, samples of actual command output, and

detailed theoretical coverage go well beyond any certificationexam, to provide you with something that can't be tested—

getting things to work the right way, and on the first time

When plan A fails, the material also provides the steps needed

to monitor network operation and quickly identify and resolvethe root cause of malfunctions

As trainers who deal with large numbers of both experiencedand inexperienced users on a regular basis, we have seen it all.Within this guide, you will find the many pearls of our

accumulated wisdom, any one of which can easily pay for thisbook many times over in increased network uptime and

performance

because they are packed with detailed information regardingtheory, configuration, and troubleshooting for each topic Ratherthan create more chapters, "soft breaks" and summaries withinthe chapters are used to identify boundaries within the materialthat afford a convenient place to take a breather, or as we oftenprovide in our training classes, a "biology break and stretch."Dog-ear the pages, write notes in the margins, augment thetopology illustrations with something more akin to your network

—just remember that this is a beastly JUNOS book: part exam,part training class, part knowledge base It's meant to be used,abused, and put to work Let's get going

P4.1 What Is Enterprise Routing?

After you've spent some time in the networking field, you tend

to notice that there is rarely a single way to do things, and inmany cases, a single precise definition for terms After all, often

a network engineer's best answer is "it depends." Such is thecase with enterprise routing, so let's start off with a definitionquestion: what is an enterprise network? Is it a large

multinational network used by a manufacturing company; is it agovernment network supporting a state or a county; is it a

regional network used by a parts distributor; or is it a networkthat supports your local dentist's office?

Of course, it's probably all of these, and many more At a veryhigh level, you can state that an enterprise network is one that

is used to support activities as opposed to generating revenue,

as in a service provider's network Some might say that if

someone pays you to access your network, you are providing aservice to him and you're no longer an enterprise network Butthat sweeping statement doesn't really apply if that someone ispaying you to cover your costs to provide that service So, asyou can see, it depends

Defining an enterprise network also manifests itself into howJuniper Networks defines its products within the enterprise

networks require density and throughput options from a

platform listed as a service provider product From the softwareside of things, the same issue arrives Whereas a technologysuch as IPSec is used by all types of networks around the globe,

is it used more by enterprise networks than by service providernetworks? Some engineers would answer yes to that question,but then, you can't say that a service provider will never useIPSec

From the perspective of hardware platforms, Juniper Networkshas designated the following as enterprise products:

J-series routers to include the J2300, J2320, J2350, J4350,and J6350

M7i and M10i routers

M120 routers

However, larger enterprise networks may find platforms such asthe M320 and MX960/480 very useful for their environments Infact, the reverse is also true in that a traditional service

provider network may very well find an appropriate need anduse for platforms designated as enterprise routers

The good news in all this is that you have a well-thought-outoperating system in JUNOS The JUNOS software is a single

train of features that operates across all of the various routingplatforms So, whether you run an enterprise network or a

service provider network, and regardless of your actual

hardware platform, there is a single version of software code toload Although this single code train has lots of hidden benefits,such as stability, ease of expandability, lower total operationalcosts, and more, what it really means is the ability to have thesame features available on all devices So, from a learning

perspective, we can talk about the software and its featureswithout having to constantly caveat our discussion with "except

hardware enhancements that are unique to a particular

platform, these cases tend to be exceptions and are infrequentenough to remember

current information on Juniper Networks' Enterprise Routingcertification tracks, visit the JNTCP web site at

http://www.juniper.net/certification

P4.3 How to Use This Book

Let's look at some specifics on how this book can help you We'lltalk about what we cover in the various chapters, how the book

is laid out, and some resources to help you along the way Tostart, let's discuss what you should know before you begin toread this book

We are assuming a certain level of knowledge on the reader'spart This is important because we are assuming you to be

conversant in the following topic areas:

OSI model

to easily discuss and apply technology to a specific OSIlevel This segmentation lets engineers divide the overallproblem of getting one application to talk to another intodiscrete parts and more manageable sections Each levelhas certain attributes that describe it and each level

interacts with its neighboring levels in a very well-definedmanner

Switches

These devices operate at Layer 2 of the OSI model and uselogical local addressing to move frames across a network.Devices in this category include Ethernet, AsynchronousTransfer Mode (ATM), and Frame Relay switches

Routers

These devices operate at Layer 3 of the OSI model andconnect IP subnets to each other Routers move packetsacross a network in a hop-by-hop fashion

Ethernet

These broadcast domains connect multiple hosts together

on a common infrastructure Hosts communicate with eachother using Layer 2 media access control (MAC) addresses

Point-to-point links

These network segments are often thought of as WAN links

geographical areas Possible encapsulations used on theselinks include ATM, Frame Relay, Point-to-Point Protocol

(PPP), and High-Level Data Link Control (HDLC)

IP addressing and subnetting

Hosts using IP to communicate with each other use 32-bitaddresses Humans often use a dotted decimal format torepresent this address This address notation includes anetwork portion and a host portion, which is normally

displayed as 192.168.1.1/24

TCP and UDP

These Layer 4 protocols define methods for communicatingbetween hosts The Transmission Control Protocol (TCP)provides for connection-oriented communications, whereasthe User Datagram Protocol (UDP) uses a connectionlessparadigm Other benefits of using TCP include flow control,windowing/buffering, and explicit acknowledgments

ICMP

Network engineers use this protocol to troubleshoot andoperate a network as it is the core protocol used by the pingand traceroute (on some platforms) programs In addition,the Internet Control Message Protocol (ICMP) is used tosignal error and other messages between hosts in an IP-based network

JUNOS CLI

Here's a short summary of the chapters and what you'll findinside:

This chapter provides a condensed but comprehensive

overview of JUNOS Protocol Independent Properties (PIPs),such as static and aggregate route, and of routing policy,which is used to control route advertisement, redistribution,and attribute manipulation

Chapter 4

This chapter provides a detailed review of Interior GatewayProtocol (IGP) operation, and then focuses on multivendordeployments of the Routing Information Protocol (RIP) andOpen Shortest Path First (OSPF) The material also focuses

on IGP migration strategies and includes an EIGRP-to-OSPFmigration case study

Chapter 5

After providing a detailed review of what the Border

Gateway Protocol (BGP) is and how it can benefit an

enterprise, this chapter provides a series of case studiesthat build in complexity, starting with a single homed

network with no Internal BGP (IBGP) speaker and endingwith a multihomed-to-multiple-providers scenario, to

include a redundant IBGP route reflection design that avoidsrunning IBGP on all internal routers The policy treatment isfocused on practical enterprise routing goals, and it detailsboth inbound and outbound policy that includes

autonomous system (AS) path regex matching and BGPattribute manipulation

Chapter 6

This chapter provides an overview of a large variety of

Path Forwarding, the Simple Network Management Protocol(SNMP), and syslog

Network Address Translation (NAT) This chapter also laysthe CLI foundation to discuss more scenarios in Chapter 8

Chapter 8

This chapter dives into the complex scenarios of the

features discussed in Chapter 7 It walks through variousdeployed NATs, IPSec virtual private networks (VPNs), IPSecover GRE, and all possible Layer 3 services combined

Chapter 9

This chapter provides an overview of IP class of service

(CoS) and includes a detailed primer on IP DiffServ Thematerial then details the similarities and differences in CoShandling between the J-series and M7i routers, which is acommon source of confusion A practical CoS case studyserves as the foundation for CoS deployment and

operational verification The chapter also demonstrates theJ-series-specific Virtual Channel CoS feature

Multicast tends to see little deployment and is a commonarea of confusion This chapter details IP multicast

concepts, provides an overview of multicast protocols, andthen demonstrates several Physical Interface Module (PIM)sparse mode scenarios, to include PIM sparse mode withstatic, bootstrap, and Anycast-RP Through all the examples,practical verification and fault isolation steps are provided

software with enhanced services, and the various things youneed to know before deploying JUNOS software with

enhanced services

In addition, you can also use this book to attain one of the

Juniper Networks certification levels related to enterprise

routing To that end, each chapter in the book includes a set ofreview questions and exam topics that have been covered, all of

it designed to get you thinking about what you've just read anddigested If you're not in the certification mode, the questionswill provide a mechanism for critical thinking, potentially

topology uses only Fast Ethernet and T1 interfaces; however,other interface types are examined in Chapter 2 You mightrecognize the hostnames of the routers—they all relate to abeverage that was created more than 7,000 years ago (withevidence to consumption) in Mesopotamia The names arechosen due to the international appeal of the resultant productand for the resultant food value only, as beer is an excellentway to preserve the nutritional value of grain

Figure P4-1 This book's topology

The following typographical conventions are used in this book:

Italic

Indicates new terms, URLs, email addresses, filenames, fileextensions, pathnames, directories, and Unix utilities

Indicates commands, options, switches, variables,

attributes, keys, functions, types, classes, namespaces,methods, modules, properties, parameters, values, objects,events, event handlers, XML tags, HTML tags, macros, thecontents of files, and the output from commands

This icon indicates a warning or caution

P4.6 Using Code Examples

This book is here to help you get your job done In general, youmay use the code in this book in your own configuration anddocumentation You do not need to contact us for permission

configurations from this book does not require permission

Selling or distributing a CD-ROM of examples from this bookdoes require permission Answering a question by citing thisbook and quoting example code does not require permission.Incorporating a significant amount of sample configurations oroperational output from this book into your product's

documentation does require permission

We appreciate, but do not require, attribution An attributionusually includes the title, author, publisher, and ISBN For

example: "JUNOS Enterprise Routing by Doug Marschke and

Harry Reynolds Copyright 2008 Doug Marschke and Harry

Reynolds, 978-0-596-51442-6."

If you feel your use of code examples falls outside fair use orthe permission given here, feel free to contact us at

permissions@oreilly.com

P4.7 Comments and Questions

Please address comments and questions concerning this book tothe publisher:

http://www.oreilly.com/catalog/9780596514426

or:

To comment or ask technical questions about this book, sendemail to:

bookquestions@oreilly.com

For more information about our books, conferences, ResourceCenters, and the O'Reilly Network, see our web site at:

http://www.oreilly.com

P4.8 Safari® Books Online

When you see a Safari® Books Online icon on the cover of yourfavorite technology book, that means the book is available

online through the O'Reilly Network Safari Bookshelf

Safari offers a solution that's better than e-books It's a virtuallibrary that lets you easily search thousands of top tech books,cut and paste code samples, download chapters, and find quickanswers when you need the most accurate, current information.Try it for free at http://safari.oreilly.com

P4.9 Acknowledgments

The authors would like to gratefully and enthusiastically

acknowledge the work of many professionals who assisted us inthe development of the material for this book Although ournames are printed on the book as authors, in reality no authorworks alone The contributions of many people have made thisbook possible, and others have assisted us with their technicalaccuracy, typographical excellence, and editorial inspiration.Many thanks are owed to the official technical editors of thismaterial Mario and Jack were extremely responsive to the

demanding needs of our schedule Your attention to detail andwealth of knowledge no doubt saved us many an embarrassingbit of errata To this end, we also thank Colleen Gorman for her

We would also like to acknowledge Juniper Networks in general,for the assistance provided on various fronts, and specifically

Monear Jalal, David Ranch, and Jerish Parapurath, for their

efforts in making Chapter 11 possible We also extend thanks to

Jonathon Looney, who volunteered to provide a technical review

for the services chapters (Chapter 7, Chapter 8, and Chapter11), for his detailed knowledge of JUNOS software with

enhanced services, and for the inspiration he provided with

regard to the BGP policy treatment We would also like to thank

Chris Heffner, who provided the routers used for this book via

http://www.certified-labs.com/, with a price that could not bematched—free of charge

P4.9.1 From Doug Marschke

I would like to acknowledge all my friends who helped me

through this very time-consuming and, at times, stressful effortwith many words of encouragement and well-timed stress

relievers I would like to thank Becca Morris in particular for herfree time spent correcting my horrible grammar to avoid

embarrassment before editorial submission I would also like tothank my roommate, Catherine la O', for putting up with theman writing in the cave Of course, I would be remiss if I didnot thank my furry quadruped friend, Josh, who was by my sidethe entire time, offering a woof to any potential distracters

I would like to acknowledge my wife, Anita, and two lovely

daughters, Christina and Marissa, for once again understandingand accommodating my desire to engage in this project Also,special thanks to my managers at Juniper Networks, CorinneRattay and Sreedhevi Sankar, for their understanding and

support I really appreciate their willingness to accommodatethe occasional glitch in my "day job" schedule that was needed

to make this happen Lastly, I'd like to thank Doug Marschke(whose name I can never spell, but shall never forget), for

offering me the chance to participate in this project I take

great pride in seeing how far Doug has come in his professionalcareer and fully expect to find myself working for him one day.You go, Doug!

Enterprise Routing

When the founding engineers of Juniper decided to create

routers, they took the view of forwarding packets as quickly aspossible (line rate) with services enabled, which spawned themarketing decree "Service without Compromise."

All Juniper Networks routers share the same common designphilosophy, which is to have a clean separation of the controland forwarding planes In the M-series, this separation is

created in hardware, whereas the J-series maintains this divide

in software The forwarding plane is referred to as the PacketForwarding Engine (PFE), and the control plane is called theRouting Engine (RE)

The RE's primary functions are to manage the PFE, control therouter's software (JUNOS), manage the command-line interface(CLI), provide troubleshooting tools, and maintain the routetables and the master forwarding table This forwarding table ispassed down to the PFE and is used to forward any transit

packet to the next hop destination In this way, the RE neverhas to be directly involved in packet forwarding (i.e., processswitching), which allows more resources for the actual controlfunctions (see Figure 1-1) One example is the ability to issue

"debug" commands without degrading the performance of therouter!

Figure 1-1 Juniper architecture design philosophy

all routes learned from all protocols (Open

Shortest Path First [OSPF], Border GatewayProtocol [BGP0, static, interfaces, etc.]) Theforwarding table provides the "best" routes thatwill be used to forward packets based on protocolpreference and metrics

The PFE's sole purpose in life is to forward packets as fast as itcan In an M-series router, the PFE consists of several

application-specific integrated circuits (ASICs) contained onvarious cards that are placed into the chassis In the J-series,the PFE is a virtualized real-time thread with the ASIC

In an M-series router, the PFE is not just one physical card inthe router, but a series of cards, each containing a different

ASIC The fundamental building block of the PFE on any M-series router is the Physical Interface Card (PIC) The PIC is thecard that the physical media such as Ethernet, Serial, or

Asynchronous Transfer Mode (ATM) will plug into This PIC

contains an ASIC that will pull and place data on the wire aswell as deal with the actual interface framing The final piece ofthe PFE is the compact Forwarding Engine Board (cFEB), whichcontains several ASICs that deal with packet storage,

forwarding, queuing, and filtering An M7i contains just a singlecFEB, whereas an M10i will contain both a primary and a

backup cFEB

The M120 router contains six FEBs that aremapped to chassis slots and provide N+1 standbyredundancy

As previously mentioned, the PFE of a J-series router is

virtualized However, like any router in our networking universe,

it must contain interfaces The J2320, J2350, J4350, and J6350enterprise routers have changeable cards similar to the PIC of

an M-series router, called Physical Interface Modules (PIMs) orEnhanced Physical Interface Modules (EPIMs) The primary

difference between a PIM and an EPIM is that EPIMs supporthigher-speed interfaces and must be installed in certain slots onthe router

It may seem that the two modules, PIC and PIM,

1.1 JUNOS Overview

JUNOS software is cool It just is The designers of JUNOS

software put tremendous thought into making a stable, robust,and scalable operating system that would be a positive for therouter They were able to learn from previous vendors'

mistakes, and created an OS that other companies will foreveruse as their model

The core philosophy of JUNOS software was to create a modular

and stable operating system The modularization was created

by the use of software daemons, and the stability was achieved

by choosing a well-known, open source, and stable kernel ofFreeBSD This kernel is usually hidden to the user, but manyfeatures of FreeBSD have been ported to the command line ofJUNOS The kernel also maintains the forwarding table

synchronization between the RE and the PFE

Riding on top of the kernel are all the fully independent

software processes for routing, CLI, interfaces, and so forth.Figure 1-2 shows a small subset of these processes; you canshow a complete list in the router by issuing a show systemprocesses command These processes are fully independent, so

a failure of one process will not affect the other For example,Figure 1-2 shows the Simple Network Management Protocol

(SNMP) process pulling information from the interface, chassis,and routing processes If this SNMP process fails or contains asoftware bug, it affects only this process and not the others.This is a major shift from other routing vendors that operatedmonolithic code where one change in the interface code could

Figure 1-2 JUNOS software architecture

Every Juniper Networks router is created from the same codebase, so all run JUNOS software Since the J-series did not

contain any ASICs for the PFE and certain interface drivers such

as high-speed OC-192 links were deemed unnecessary, a newimage had to be created for these devices This is still JUNOS,however, with almost the same feature set as the ASIC-drivenimage

This means that there is a single image perversion for all M/T-series routers regardless ofmodel number, and a single image per version forall J-series routers The days of creating and

maintaining large spreadsheets or lists per routerare now gone

new software process called fwdd (forwarding devices daemon),

which acts as the virtualized PFE It is essentially a series ofreal-time threads operating over the kernel, as shown in Figure1-3 Instead of an ASIC providing the functionality of the PFE,sockets and APIs will interface with the kernel, providing a

deterministic performance

Figure 1-3 J-series software architecture

Enterprise Routing

When the founding engineers of Juniper decided to create

routers, they took the view of forwarding packets as quickly aspossible (line rate) with services enabled, which spawned themarketing decree "Service without Compromise."

All Juniper Networks routers share the same common designphilosophy, which is to have a clean separation of the controland forwarding planes In the M-series, this separation is

created in hardware, whereas the J-series maintains this divide

in software The forwarding plane is referred to as the PacketForwarding Engine (PFE), and the control plane is called theRouting Engine (RE)

The RE's primary functions are to manage the PFE, control therouter's software (JUNOS), manage the command-line interface(CLI), provide troubleshooting tools, and maintain the routetables and the master forwarding table This forwarding table ispassed down to the PFE and is used to forward any transit

packet to the next hop destination In this way, the RE neverhas to be directly involved in packet forwarding (i.e., processswitching), which allows more resources for the actual controlfunctions (see Figure 1-1) One example is the ability to issue

"debug" commands without degrading the performance of therouter!

Figure 1-1 Juniper architecture design philosophy

all routes learned from all protocols (Open

Shortest Path First [OSPF], Border GatewayProtocol [BGP0, static, interfaces, etc.]) Theforwarding table provides the "best" routes thatwill be used to forward packets based on protocolpreference and metrics

The PFE's sole purpose in life is to forward packets as fast as itcan In an M-series router, the PFE consists of several

application-specific integrated circuits (ASICs) contained onvarious cards that are placed into the chassis In the J-series,the PFE is a virtualized real-time thread with the ASIC

In an M-series router, the PFE is not just one physical card inthe router, but a series of cards, each containing a different

ASIC The fundamental building block of the PFE on any M-series router is the Physical Interface Card (PIC) The PIC is thecard that the physical media such as Ethernet, Serial, or

Asynchronous Transfer Mode (ATM) will plug into This PIC

contains an ASIC that will pull and place data on the wire aswell as deal with the actual interface framing The final piece ofthe PFE is the compact Forwarding Engine Board (cFEB), whichcontains several ASICs that deal with packet storage,

forwarding, queuing, and filtering An M7i contains just a singlecFEB, whereas an M10i will contain both a primary and a

backup cFEB

The M120 router contains six FEBs that aremapped to chassis slots and provide N+1 standbyredundancy

As previously mentioned, the PFE of a J-series router is

virtualized However, like any router in our networking universe,

it must contain interfaces The J2320, J2350, J4350, and J6350enterprise routers have changeable cards similar to the PIC of

an M-series router, called Physical Interface Modules (PIMs) orEnhanced Physical Interface Modules (EPIMs) The primary

difference between a PIM and an EPIM is that EPIMs supporthigher-speed interfaces and must be installed in certain slots onthe router

It may seem that the two modules, PIC and PIM,

1.1 JUNOS Overview

JUNOS software is cool It just is The designers of JUNOS

software put tremendous thought into making a stable, robust,and scalable operating system that would be a positive for therouter They were able to learn from previous vendors'

mistakes, and created an OS that other companies will foreveruse as their model

The core philosophy of JUNOS software was to create a modular

and stable operating system The modularization was created

by the use of software daemons, and the stability was achieved

by choosing a well-known, open source, and stable kernel ofFreeBSD This kernel is usually hidden to the user, but manyfeatures of FreeBSD have been ported to the command line ofJUNOS The kernel also maintains the forwarding table

synchronization between the RE and the PFE

Riding on top of the kernel are all the fully independent

software processes for routing, CLI, interfaces, and so forth.Figure 1-2 shows a small subset of these processes; you canshow a complete list in the router by issuing a show systemprocesses command These processes are fully independent, so

a failure of one process will not affect the other For example,Figure 1-2 shows the Simple Network Management Protocol

(SNMP) process pulling information from the interface, chassis,and routing processes If this SNMP process fails or contains asoftware bug, it affects only this process and not the others.This is a major shift from other routing vendors that operatedmonolithic code where one change in the interface code could

Figure 1-2 JUNOS software architecture

Every Juniper Networks router is created from the same codebase, so all run JUNOS software Since the J-series did not

contain any ASICs for the PFE and certain interface drivers such

as high-speed OC-192 links were deemed unnecessary, a newimage had to be created for these devices This is still JUNOS,however, with almost the same feature set as the ASIC-drivenimage

This means that there is a single image perversion for all M/T-series routers regardless ofmodel number, and a single image per version forall J-series routers The days of creating and

maintaining large spreadsheets or lists per routerare now gone