Cisco press IP addressing fundamentals oct 2002 ISBN 1587050676

Publisher: Cisco Press Pub Date: October 31, 2002 ISBN: 1-58705-067-6 Thorough and understandable explanations of the binary mathematics behind IP addressing Complete coverage of the IPv

By Mark A Sportack

Publisher: Cisco Press Pub Date: October 31, 2002 ISBN: 1-58705-067-6

Thorough and understandable explanations of the binary mathematics behind IP addressing

Complete coverage of the IPv4 address space without distractions of routing or transport protocols

Detailed explanations of subnetting and supernetting, Variable Length Subnet Masks (VLSMs), CIDR, NAT, portable address spaces, and IPv6 Strategies for managing an address space for enterprise WANs, data centers, and ISPs

Numerous examples and an easy-to-read style of writing that imparts a profound understanding of IP addressing

The Internet Protocol (IP) is the native protocol suite of the Internet and has become predominant in virtually all networks and internetworks Managing an IP address space requires a solid command of binary mathematics, particularly as it is applied within the IP addressing architecture The mathematics of the IP address space, however, are not intuitive and can be very difficult to grasp Consequently, learning about IP addressing can

both networks and internetworks Author Mark Sportack prepares you for real-world success by walking you through some of the issues and traps that lie in wait for anyone who needs to plan or manage the use of an IP address space Most importantly, this book doesn't presume you already know what the entire IP addressing puzzle looks like.

IP Addressing Fundamentals imparts a profound command of IP addressing through a

clear and concise writing style Basics are reinforced with detailed information and

numerous examples of how the concepts work This book builds upon concepts presented

in earlier chapters and concludes with fairly advanced topics that will become increasingly useful to midlevel network engineers.

After reading IP Addressing Fundamentals, you'll finally understand IP addressing and

appreciate both its mechanics and relevance, and you'll know how to efficiently apply your new knowledge.

By Mark A Sportack

Publisher: Cisco Press Pub Date: October 31, 2002 ISBN: 1-58705-067-6

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The opinions expressed in this book belong to the author andare not necessarily those of Cisco Systems, Inc

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Dedications

I dedicate this book to my precious wife, Karen, for her

unflagging love and support throughout the arduous process ofdeveloping this book I'll never know why you tolerate my

eccentricities and avocational distractions, but I'm perpetuallygrateful

I also dedicate this book to my two children, Adam and Jennifer.You have brought joy and meaning into my life in ways I can'texplain

evaluation of emerging network technologies, specification ofthe technology base for the networks that the company's

Internet-based managed hosting services During the course ofthe last 20 years, Sportack has worked in virtually every aspect

of information technology, from administering networks andservers to managing technology and technical personnel He

also has written a variety of books, including IP Routing

Fundamentals, published by Cisco Press, Networking Essentials Unleashed, and many others.

Mark Gallo is a technical manager with America Online His

network certifications include Cisco CCNP and Cisco CCDP Hehas led several engineering groups responsible for designingand implementing enterprise LANs and international IP

networks He has a BS in electrical engineering from the

University of Pittsburgh He resides in northern Virginia with hiswife, Betsy, and son, Paul

Alex Kamantauskas is the hostmaster for ClearBlue

Technologies, Inc He has worked in a wide variety of positions

in the Internet sector since 1993, including system and networkengineering, network security, and IP allocation services In hisspare time he composes electronic music

Dave Kurtiak is a principal engineer and Director of Network

Computing Services for Loral Skynet, where he leads a team oftechnical professionals responsible for managing the company's

IT and data network infrastructure He has more than 14 years

of experience in the IT and telecommunications industries

Before joining Loral Skynet, he was a senior data

end network analysis, planning, and troubleshooting Kurtiak isexperienced in many telecommunications technologies,

communications specialist for AT&T He specializes in end-to-including Ethernet, switches, routers, VPN, point-to-point digitalfacilities, Frame Relay, and premise wiring topologies He is alsorecognized as the resident expert in TCP/IP networking He has

a master's degree in telecommunications from the University ofColorado at Boulder and a bachelor's degree in information

systems from the University of North Carolina at Greensboro

Martin Walshaw, CCIE #5629, CCNP, CCDP, is a systems

engineer working for Cisco Systems in the Enterprise Line ofBusiness in South Africa His areas of specialization include

convergence, security, and content delivery networking, which

so, he has dabbled in many aspects of the IT industry, rangingfrom programming in RPG III and Cobol to PC sales When

Walshaw is not working, he likes to spend all his time with hispatient wife, Val, and his sons, Joshua and Callum Withouttheir patience, understanding, and support, projects such asthis would not be possible

I am indebted to many people for their assistance and supportthroughout the process of writing this book Those people

Jeff Harrington for allowing me the use of his technical libraryand reference materials

IP Addressing Fundamentals is designed to explain how the IP

address space works and how it is used Many books help yougain a working knowledge of this topic, but none can help youboth appreciate the why behind the theory and the how behindthe application My goal is to do both with this book

The inspiration for this book came as a result of my teachingexperiences at Syracuse University I'm an adjunct professor inSU's School of Information Studies and Technology, where Iteach a pair of graduate courses on telecommunications anddata networking Despite the advanced nature of these courses,and the talented students who are attracted to them, I foundmyself continuously astounded at the limits of their workingknowledge of important topics such as IP addressing After twoyears of correcting misperceptions, asking students where theypicked up their misinformation, and trying to show them a

better way to understand the Internet's address space and

technologies, I found myself getting frustrated Just when I

started thinking that maybe teaching wasn't such a good idea, Ihad a pair of experiences that erased my doubts and replacedthem with inspiration

One particularly bright young man explained to me that

learning about IP was a lot like trying to piece together a jigsawpuzzle The only differences were that you didn't know what thepuzzle was supposed to look like when it was finished, nor didyou have the benefit of a picture fragment on each piece Heappreciated my approach to teaching IP and networking,

because I gave them the "big picture," broke it down into

subtopics that were easier to grasp, and then correlated thosesubtopics back to the big picture A healthy dose of reality, inthe form of examining the practical uses and impacts of eachsubject, was also injected into each class In the end, he said

The other experience occurred in the same semester One nightbefore class, a student approached me with a new book in hishands You could tell it was a new book, even from a distance:that shiny, unmarred cover; the smell of fresh ink; the

uncracked spinea thing of beauty! But the look on his face wasone of disappointment and anxiety The book was written by aluminary in the Interneta founding father who has written

countless RFCs and has been instrumental in guiding the

Internet's growth and development Yet my student said thebook was disappointing I suggested that the book should betechnically solid given the achievements of its author He simplyreplied that it would be a great book if he could understand it!Instead of educating and informing the reader, this book causedanxiety and self-doubt My student was asking my advice onwhether he was smart enough to succeed in this industry Ofcourse he was, I assured him It was the book and its authorwho had failed

These two events crystallized in my mind the need for this

book I called John Kane, Editor-in-Chief at Cisco Press We had

a long chat about the need for a reader-friendly book that

explains the fundamentals of the IP address space from theground up A book that unravels the mysteries of subnetting,supernetting, and CIDR A book that thoroughly explains thebinary mathematics of IPv4's addressing space and shows thereader how an IP address becomes an active component in bothnetworks and internetworks A book that prepares you for

success by walking you through some of the issues and trapsthat lie in wait for anyone daring to either plan or manage theuse of an IP address space Most important of all, a book thatdoesn't presume that you already know what the puzzle shouldlook like when it is completed Thankfully, John and the folks atCisco Press agreed I hope you enjoy it!

Throughout this book, you will see a number of icons used todesignate Cisco and general networking devices, peripherals,and other items The following icon legend explains what theseicons represent

Throughout this book, you will see the following icons used forcommon network devices

The conventions used to present command syntax in this bookare the same conventions used in the IOS Command Reference.The Command Reference describes these conventions as

follows:

Vertical bars (|) separate alternative, mutually exclusiveelements

Square brackets ([ ]) indicate an optional element

Braces ({ }) indicate a required choice

Braces within brackets ([{ }]) indicate a required choicewithin an optional element

Boldface indicates commands and keywords that are

entered literally as shown In actual configuration examplesand output (not general command syntax), boldface

Technologies

To many technical personnel today, the Internet remains a

mystery that is taken for granted Virtually everybody knowswhat it is and what it can be used for, but few actually knowwhat goes on behind the scenes The Internet's address spaceand native protocols have become the de facto standard formany aspects of networking The Internet Protocol (IP) addressspace and the various IP-based protocols and mechanisms havebeen widely deployed around the world Currently they supportmore networks than just the Internet More importantly, thesetechnologies and concepts share a similar origin: Typically, theyare developed and ratified in an open and consensus-basedforum

It is this consensus-based approach to developing technologiesthat creates such confusion among newcomers to the Internet.Worse, the confusion extends beyond the Internet and

encompasses all its component technologies, including the IPaddress space Understanding any of these technologies

requires an appreciation of the context in which it was

developed, and a sense of what it was originally intended to do

This chapter explores how technologies are ratified for use inthe Internet It also looks at the various standards bodies andother organizations that are the Internet's caretakers This willhelp you better appreciate what does and does not carry theweight of law on the Internet

Numerous organizations, standards bodies, and even

corporations function in different capacities All of them

contribute in some way to the Internet Some allocate domainnames (such as cisco.com) or assign IP addresses to the

Internet's end users Others create the technologies that makethe Internet work or that let you use the Internet All theseentities are integral to the Internet's operation We'll look ateach one in this chapter, but only one can truly be consideredthe Internet's caretaker That organization is the Internet

Engineering Task Force (IETF)

IETF

The manner in which the Internet's technology base is

developed and ratified might not be intuitively appreciated Infact, the arrangement is one of the more unconventional

approaches you may ever find As we start to explore just how

it operates, and how standards and other recommendations aredeveloped in this forum, you'll appreciate why I call it

unconventional Nevertheless, it is a model that works usingboth collaborative and competitive forces

One of the unique qualities of the IETF is that it consists almostentirely of unpaid volunteers Don't misunderstand the point;these are highly technical and well-paid engineers who

contribute their time to the IETF in addition to the work they dofor their employers Such volunteers don't pay dues to join theIETF They simply "join" and either lurk in the background oractively contribute to the work being performed

The IETF, and the way it operates, can be traced back to thenascent days of the Internet when just a few hosts were

technical personnel responsible for supporting the various

interconnected hosts realized that there was great benefit toworking together for the sake of deriving consistency in namingconventions, the technology base, communications protocols,and guidelines for using their internetwork Lacking a centralbudget, mission, or any of the other trappings of a conventionalorganization, nothing could be dictated Only the mutual desire

to improve the functionality of their interdependent networkbound them together Everything had to make sense for theentire community to form a consensus Otherwise, suggestionsand recommendations might not be adopted The technical

meeting of the IETF was held in January of 1986 and was

attended by just 21 people Membership and participation haveincreased steadily since then and now encompass thousands ofpeople Although the IETF has grown tremendously, its originalessence remains embodied in the way it is organized Today,technical professionals from competitive companies work side-by-side under the auspices of the IETF to develop and maintainthe Internet's technology base Its membership is an ever-

growing group of highly talented individuals who volunteer theirtime to collaboratively engineer and evolve the Internet's

level details of new technologies, as well as methods and

technology base The IETF's work in spelling out the protocol-procedures, is published openly in a series of documents, whichinclude the following:

Internet drafts

organized and functions, is recorded in a publicly available

document that fits into one or more of the previously mentioneddocument classes

growth of the global Internet It does so in fairly abstract andless-than-obvious ways For example, it theoretically providesoversight to the IETF and its subcomponents, but that oversight

is limited to financial, logistic, and legal support For example, itprovides insurance coverage for people involved in the IETF'sstandards-creation processes, and it functions as a public

relations channel whenever an IETF entity needs to

communicate via the press

Perhaps the most visible output of the ISOC is that its trusteesratify the rules and procedures by which standards are

developed for the Internet by the IETF Thus, although the ISOCdoesn't directly shape the Internet or its technology base, itsets the rules by which the Internet evolves

One of the more critical subentities of the IETF is the IAB

Originally known as the Internet Activities Board, the IAB hasevolved and grown over time in response to changes in theInternet Today, the IAB is known as the Internet ArchitectureBoard It is responsible for long-range planning and

coordinating activities across the various subcomponents of theIETF As such, it is uniquely positioned to see the big picture ofthe IETF's cumulative efforts Part of its role might be to bringissues to the attention of specific area directors if they think along-term item requires some attention

IRTF

The IRTF is sponsored and overseen by the IAB This groupconducts research into emerging technologies, and this

research becomes an input to the IAB's long-range technologyplanning activities

IANA

The IANA is responsible for keeping track of all numbers andnumeric values that must be reserved or assigned for the

various protocols and technologies maintained by the IETF towork properly The most obvious example is the IP addressspace (the sum total of all IP addresses), but IANA's

responsibilities also include maintaining the list of TCP and UDPstandardized or well-known application port numbers

IANA is also the Internet's core registrar This dubious

distinction was conferred by the IAB, and it made IANA the

"owner" of the root of the Internet's name space This role hasnot exactly resulted in a positive perception throughout the

technically charged with maintaining all the unique parametersused on the Internet (addresses, domain names, and port

numbers) today, IANA appears to be slowly melding into ICANN

ICANN

The ICANN is a nonprofit corporation that was established tomaintain IP address allocation, assignment of protocol

parameters (such as port numbers), and management of theInternet's domain name system (DNS) These functions hadpreviously been performed by IANA, but they have since beendelegated to ICANN

There are three registries, but some cover more than one

region Table 1-1 lists the regions and their supporting RIRs

Table 1-1 RIRs and Their Regions

Réseaux IP Européens Network Coordination Centre

Each registry is given a block of IP addresses and is responsiblefor assigning and managing that space within its region Twoother geographic regions have announced plans to form theirown RIRs: Africa and Latin America ICANN is the only entitythat can charter an RIR and assign it an address space

Within each RIR's region, other entities can apply to becomeLocal Internet Registries (LIRs), much like an Internet ServiceProvider (ISP) can assign address blocks to its customers'

operational networks

Registrars, on the other hand, are responsible for managing theassignment of Internet domain names This is a much morecontentious issue than merely parsing out numbers Don't

worry just yet about why domain names can be contentious;we'll cover that in detail in Chapter 8, "Internet Names." For

Internet's growth, evolution, and operation

market, Network Solutions (and now VeriSign) maintained the registry function, and the registrar function was split among the various competing companies,

including Network Solutions That company was both registry and registrar for a while, but I assure, you they didn't play favorites In order to become an

nominations committee and serve a two-year term The areadirectors oversee a specific technical area Current areasinclude the following:

Applications

initiatives fall into this category, but those that do can be

assigned to whichever area or areas are deemed appropriate

It's important to note that the oversight of the IESG and itsarea directors doesn't extend to direct oversight of technicaldevelopment efforts Instead, oversight is construed as ratifyingthe output of the working groups Thus, the IESG can exert

influence on whether any particular proposal advances to thepoint where it can be implemented Typically, the IESG acceptsthe recommendations of working groups, but it can reject arecommendation if it believes the group has either strayed fromits charter or has recommended something that will have anadverse effect on the Internet and its technology base

Working Groups

specific technical problems is performed by transient

organizations within the IETF known as working groups The

IETF has sought to create a continuity of technical expertise inworking groups by organizing them into functional areas Eachfunctional area is directed by an IESG area director An area canhave multiple working groups operating simultaneously, focused

on extremely specific activities It is important to note that

these areas do not necessarily translate cleanly into areas

recognized by the IESG Consider this imperfect correlation

between working groups and IESG areas; a feature that enablesflexibility, as opposed to a flaw which promotes confusion Theoutput of any given working group may be reviewed by multipleIESG area directors to obviate potential conflicting technologies

or recommendations

Currently, the IETF has active working groups in the followingfunctional areas:

Applications Broadly defined as things that use IP

networks and security mechanisms, but excluding all

security and network mechanisms Applications that requirenetwork connectivity rely on well-defined interfaces to thetransport and network layer protocols, and that becomesthe bailiwick of the Applications Area working group

Internet The Internet Area encompasses developing

mechanisms and capabilities for IP itself For example,

developing the ability for IP to be transported over new

network technologies such as InfiniBand, Fibre Channel, andcable networks lies in this functional area

Operations and Management Anything that defines how

things operate is the responsibility of the O&M functionalarea Generally speaking, anything involving Simple

Network Management Protocol (SNMP), Management

Security teams are currently working on such things as thecreation of an XML-based (extensible markup language)digital signature and an open version of Pretty Good Privacy(PGP) encryption software, among others

Sub-IP The Sub-IP Area is one of the hardest areas to

describe At least, I have a difficult time understanding

what differentiates it from the Internet functional area

Substantial overlap between the two groups is evident whenyou consider that two of the currently active Sub-IP groupsare developing the specifications for IP over optical facilitiesand Multiprotocol Label Switching (MPLS)

Transport The Transport functional area focuses on

developing interfaces for higher-level protocols and

services Some of the specific areas of current activity

include IP Telephony, IP Storage, Differentiated Services(DiffServ), and audio/video transport

User Services Anything that defines how people want

"The Internet Standards Process.") This group also helpsusers of all levels improve the quality of information

available on the Internet That might sound a bit vague, butyou can think of it this way: The User Services group is

more of a communications vehicle for the IETF than a

technology development group

If these categorizations sound a bit soft, and it seems there isgreat potential for overlap, you're right Many specific technicalproblems are worked on jointly by two or more working groups.Membership in a working group is voluntary

If the notion of joining a working group and helping developnew standards for the Internet appeals to you, do yourself andeveryone in the IETF a favor, and read RFC 3160 Entitled "TheTao of the IETF," this document helps you better understand theorganization, its culture, and everything about the work it

produces The URL is www.ietf.org/rfc/rfc3160.txt

The way that technical standards are developed for the Internetmight seem arcane from the outside looking in, but this process

is eminently logical, and it has served the Internet well for

years This process is documented in the IETF's RFC 2026,

which is also currently the Internet's BCP #9 This documentcan be accessed at www.ietf.org/rfc/rfc2026.txt

If the terms RFC and BCP are alien to you, read on The

remainder of this chapter is devoted to helping you understandthe inner workings of this vital function The roles of Internetdrafts, RFCs, STDs (standards), and BCPs are all explored andexplained

Internet Draft

Virtually every standard published by the IETF starts out as an

Internet draft or I-D or just plain draft in IETF parlance A draft

can be submitted by an individual or can be the product of aworking group

The draft itself conforms to the template used for all RFCs,

which only adds to the terminology confusion Because the

RFCs are public documents, virtually anyone in the world canreview them and make comments to the author(s) for

consideration If appropriate, the document might be

superseded by a modified version, or it might die a quiet death

if it fails to resonate within the Internet community If it doesfind some support, the document can either become embraced

as a de facto standard or undergo the more rigorous

standardization process The remainder of this chapter

examines all the document types that the IETF recognizes Thenwe'll look at the inner workings of that organization's

RFCs

The most commonly encountered IETF-produced document isthe RFCs These documents aren't necessarily just requests forcomments In fact, many of them contain the specifications forprotocols and technologies that are embraced as standards orbuilt as products In other words, many RFCs have progressedwell beyond the development stage where comments are beingsolicited Thus, the full name is actually a misnomer For thisreason, RFCs of all types are almost always referred to as

simply RFCs

NOTE

Although the arcane nature and nomenclature of RFCs might bediscouraging, rest assured that some of these documents arequite useful E-mail, as ubiquitous an application as you couldhope to find, was first described in RFC 821 Similarly, DNSoriginated in a pair of RFCs numbered 1034 and 1035 So, yousee, they can be quite useful

There are six different types of RFCs Each goes through a

slightly different process during its journey toward ratification:Proposed standards

Draft standards

Internet standards

Informational documents

Historic standards

Of these six, only the first three qualify as standards within theIETF Thus, it is imperative to understand that RFCs are not

created equal Some are solid enough to have products

designed around them, and others are not intended for use

other than to solicit comments or test for interest in an

emerging technology For a much more complete summary ofthe differences between the various types of RFCs, refer to RFC

1796, "Not all RFCs are Standards." You can find it at

www.ietf.org/rfc/rfc1796.txt

Just to prove that things can get even more complicated, thereare also three subseries of documents within the RFC

architecturestandards (STDs), Best Current Practices (BCPs),and For Your Information (FYI) documents Each is described inthe following sections

Internet Standards

There are three types standardsthe Proposed Standard, theDraft Standard, and the Internet Standard RFCs that are

placed on the standards track first become Proposed Standards.After six months in this status, such RFCs might undergo

additional scrutiny and be sanctioned as Draft Standards Evenmore scrutiny is required for a Draft Standard to be ratified as

an Internet Standard Internet Standards are often known asFull Standards, but there aren't very many of them In fact,most standards-track documents never move beyond ProposedStandard That doesn't mean they aren't useful In fact, manyprotocols and products are built around Proposed Standards

or anything of the sort Advancing Proposed Standards is

complex, time-consuming work In fact, it can take several

years of work before a Draft Standard can become a Full

Standard The amount of effort required to make this happenlimits the number of RFCs that become Full Standards to justthose few protocols that are absolutely essential for the

Internet to function

We will examine the IETF's approval process for moving an RFC

on the standards track through the various standard stages in amoment

BCPs

A subset of the RFC series is known as the Internet's Best

Current Practices (BCPs) This subset differs from the technicalspecifications often found in RFCs BCPs specify operating

procedures that are consensually agreed to be the best for theInternet Alternatively, a BCP can be used to describe how toapply the various technologies described in other IETF

documents Some of the examples of BCPs presented in thischapter should give you a good idea of the type of content thatcan be found in a BCP

FYIs

The FYI subseries of documents was created to present

information such as big-picture overviews of highly technicaltopics Such overviews provide a context within which much

as an Internet draft Comments are received, and the draft isedited accordingly This can be an iterative process, as opposed

to achieving completion in a single pass If an individual createdthe draft, that person might request that an area director takethe document to the IESG for review and consideration If aworking group created the document, the chairperson of thatgroup takes it (after achieving consensus in the group, of

course) to the area director for forwarding to the IESG Eitherway, the IESG must review it in the larger context of existingstandards and future desired technology directions If any

changes are deemed necessary by the IESG, the draft goes

back to its creator(s) for further work When there is consensusamong the document's creators, area director, and IESG, thedraft can be published as an RFC

It is important to note that additional layers of checks and

balances exist in the approval process For example, if two ormore area directors object to an Internet draft, it is blockedfrom becoming an RFC, and it can't become a standard Thisveto power ensures that a technology doesn't get ratified thatwill have unacceptable impacts on other technologies This iscritical to ensure the ongoing stability of the Internet's openprotocols and technologies

Another check-and-balance mechanism is the "last call." After a

directors or working groups Any and all of these parties havethe opportunity to submit comments, concerns, and questions

to the working group responsible for the document

After all parties have had a chance to examine the draft (and itsimplications), the IESG might decide to sanction the draft as anInternet Standard If that is the case, the draft still has somehurdles to overcome The IESG requests that the editor of theRFCs (a formal position within the IETF) publish the draft as aProposed Standard It has status as a numbered RFC, but it isalso explicitly identified as a Proposed Standard After six

months, the author(s) of that RFC can ask their area director toapprove it as a draft standard This is a high hurdle to

overcome The technology must be proven by at least two

independent implementations that demonstrate not only

interoperability but also validation of the concept's benefits

As mentioned earlier, it is highly likely that a proposed standardwill never make it to full Internet Standard status and yet willstill achieve broad acceptance in the market This can be one ofthe more confusing aspects of the IETF's standards-setting

process But if an RFC makes it all the way to Full Standard,you can rest assured it has been thoroughly examined and

tested Of course, this is not a guarantee that all products willwork perfectly It just means that the various companies thatimplement the RFC start with a stable base but are free to

interpret it according to their needs The next section explainsthis phenomenon and some of its unintended consequences

NOTE

There is a persistent and pervasive misperception among