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Gerry Howser Computer Networks and the Internet A Hands-On Approach Computer Networks and the Internet Gerry Howser Computer Networks and the Internet A Hands–On Approach Gerry Howser Kalamazoo College Kalamazoo, MI, USA ISBN 978-3-030-34495-5 ISBN 978-3-030-34496-2 (eBook) https://doi.org/10.1007/978-3-030-34496-2 © Springer Nature Switzerland AG 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. 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This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland This book is dedicated to my muse, first reader, and loving spouse Patricia Berens. Itisalsodedicatedtoallmystudentswhoactedasguineapigsthroughthisideain itsmanyhalf-bakedforms.Ithasbeengreatfun. Preface “Anysufficientlyadvancedtechnologyisindistinguishablefrommagic.” ArthurC.Clark[21] The Internet Everyoneuses the Internet1, so of course everyoneknowshow it works:fromthe user’s point of view. However, I have found over the years that few people really understandwhathappensbehindthescenes.Oddlyenoughitisnotall“smokeand mirrors”or some arcane knowledgethatcan only be understoodby a chosenfew. Anyonewiththeabilitytopluginafewcablesandeditatextfile(seeSection8.9) canbuildaself–containedInternetorIntranet. Thegoalofthisbookistoprovideenoughbackgroundintotheinner–workings of the Internet to allow a novice to understand how the various protocols on the Internetworktogethertoaccomplishsimpletaskssuchasasearch.Thehopeisthat inbuildinganInternetwithallthevariousservicesapersonuseseveryday,onewill gainanappreciationnotonlyoftheworkthatgoesonunseenbutalsoofthechoices madebythedesignerstomakelifeeasierfortheuser.Thishasnotalwaysbeenthe caseinthecomputerindustry. Hopefullyyouwillfindthisbookusefulinmanydifferentways.Itcanbeused asastep–by–stepguidetobuildyourownIntranet.Itcanalsobeusedasatextfora courseinInternetprotocolsandservices.Oritcanbeusedasareferenceguidefor howthingsworkontheglobalInternet2. 1Throughoutthisbook,Internetwillbeusedtorefertotheglobalnetworkweallknowandlove andinternet(lowercase)willbeusedtorefertoanygenericInternetorintranetthatdoesnotrequire accesstothepublicInternettofullyfunction. 2 This book draws heavily on my experience teaching CompTIA Network+ [23] classes using TamaraDean’sexcellentbook[27]. vii viii Preface To the instructor Thisbookisdesignedfordualpurposes.Eachchapterconsistsofbackgroundinfor- mationonaspecifictopicorInternetserviceandwhereappropriateafinalsection on how to configurea Raspberry Pi to provide that service. If these configuration sectionsareskipped,ThisbookcanbeusedforacourseontheInternetandrouting. Whenusedwiththesuggestedequipment,themainpartofthisbookcanbeused for background material for a hands–on lab course in building a fully–functional InternetusinginexpensiveRaspberryPi’s.Ifyouhaveaccesstoanumberof“white box”computersrunningLinux(Debian[28]isagoodchoice),thisbookcanbeused withminoradjustmentstobuildanInternetofLinuxboxes. Onepossibleapproachtousingthisbookwouldbetoassignthechapterstobe read beforeclass. Class time would be used to answer questionsfromthe reading andgooverthechaptersthatrelatespecificallytotheconfigurationoftheRaspberry Pi.Thebulkoftheclasstimeshouldbereservedforactuallyconfiguringthenetwork inalabsetting.Thishasprovedsuccessfulinthepast3. Additionalresourcescanbefoundat: https://www.springer.com/book/9783030344955/ https://www.gerryhowser.com/book/9783030344955/. To the student orhobbyist Ihopethatthistextbookprovidesyouanenjoyableintroductiontotheinnerwork- ings of the Internet. If you already have some familiarity with a topic, you will findthechaptersorganizedsothatyoucanskimintroductorysectionsandproceed quicklytothemoreadvancedmaterial.Myintentistoprovideyouwithacleartext thatyouwillfindusefulinbuildingyourownnetworksandasafirstreferencefor understandingthemanyInternetprotocols. Thisbookisdesignedasaprojectforgroupsoffourstudentseachwiththeirown RaspberryPi;however,smallergroupscaneasilyrunalloftherequiredprotocolson asfewasoneRaspberryPi.Infact,youwillbeencouragedtoinstallandconfigure alloftheservicessothatthegroupcanstillfunctionwhenamemberisunavailable. WhileitmaybepossibletousejusttheconfigurationsectionstobuildanIntranet, itisstillbesttoreadthebackgroundmaterialfirst. Attheendofeachchapterareexercisesrelevanttothattopic.Asusualtheeasier exercises are first with progressively more challenging problems as the numbers growlarger.Youwillfindsolutionstosomeoftheexercisesattheendofthisbook. 3 ThisbookwasinspiredbycoursestaughtatLoyNorrixHighSchoolandKalamazooCollege. BothareinKalamazoo,Michigan. Preface ix Whataretheprerequisitesforthisbook? • Youshouldhavesomefamiliaritywithcomputersbeyondsimplyusingapplica- tions,butyoucangetbywithoutit. • Programmingexperienceishelpfulbutnotnecessary.Thesameistrueofexpe- rienceinstallingandconfiguringsoftware. • YoushouldbecomfortablewiththeInternetasauser. • Youmustbewillingtothinkbeforeyoustartmakingchanges.RaspianisaLinux distributionandassuchitissometimesdifficulttoreversechangesmadeinhaste. Ifyoubackupeachconfigurationfilebeforeyouchangeityoucanalwaysback- outanychanges. • Youmust becuriousandfearless.Remember:theworstthatcanhappenisyou mayneedtoreinstalltheoperatingsystem.Ifthereisachanceofharmingyour hardware,youwillbewarnedinadvance. • Simple solutions are usually the fastest, least difficult to understand, and least pronetofail. • Innetworkingthegoalisusuallytomovedataasfastaspossible(highthrough- put)andcorrectlyaslongasthatdoesnotslowthingsdown.Thisseemscounter intuitiveatfirst,buttheend–pointsoftheconversationaretaskedwithhandling errors,notthenetwork. Additionalresourcescanbefoundat: https://www.springer.com/us/book/9783030344955/ https://www.gerryhowser.com/book/9783030344955/. To the professional YoushouldfindthisbookusefulasanoverviewtohowtheInternetworksandhow many of the protocols work. However, this is not an exhaustive reference to the Internet as the Internet is growing and changing at a staggering rate. Indeed, the only true referencesfor the Internet, the final authority as it were, are the current RFCswhichcanonlybefoundontheweb.Themostreliableplacetolookisonthe IETFwebsitehttps://tools.ietf.org/rfc/index. IfthisbookisusedasaguidetosetupanIntranet,pleasepaycloseattentionto thesectionsmarked“Security”.Theseactionsshouldbetakenalongwithanyother securityactionsrequiredbyyourorganization4. 4Inmyopinion,perfectsecurityisnotpossibleifyournetworkisconnectedtoanything. x Preface Acknowledgments forthe firstedition I would like to thank the anonymousfirst readers of this book. Their suggestions madethisabetterwork.Thankyou. Thisworkwouldnotbepossiblewithoutthehelpofmymanystudentsoverthe years.ThiscoursewasfirsttaughtasasecondyearprogramundertheKalamazoo RegionalEducationService Area (KRESA) as part of Educationfor Employment (EFE).Thesepoorstudentsweresubjectedtoworkingwithantiquatedequipment, Linux(whichtheywerenot usuallyfamiliarwith),verylimitedoutsideresources, andmanydifficultchallenges5.Theylovedit. Amorestructuredversionofthiscoursewastaughtin2016atKalamazooCol- lege in Kalamazoo,Michiganas Buildingthe Internetin a Roomusing Raspberry Picomputersasdescribedinthisbook.Apparentlyallwentwellassomestudents wantedtotakethecourseagain. ToallthesestudentsI wouldlike tosay:youputa lotofsweatintotheclasses uponwhichthisbookisbuilt.Ican’tthankyouenough. Kalamazoo,Michigan GerryHowser Fall,2019 5Thingsneverworkedoutasplanned.Thatwaspartoftheattractionandchallenge. Contents Preface............................................................ vii ListofAcronyms................................................. xxiii ListofAlgorithms................................................. xxix ListofFigures ................................................... xxxi ListofTables .................................................... xxxv 1 Introduction................................................... 1 PartI TheIPNetwork 2 TheOSISevenLayerModel..................................... 7 2.1 AnalogSignals ............................................ 7 2.2 DigitalSignals............................................. 8 2.3 AsynchronousandSynchronousCommunications ............... 9 2.3.1 Synchronous........................................ 10 2.3.2 Asynchronous....................................... 10 2.4 TheSevenLayerOSIModel ................................. 11 2.5 CommunicationsLayers..................................... 13 2.6 Layer1:ThePhysicalLayer ................................. 14 2.7 SharedMedia.............................................. 15 2.7.1 TimeDivisionMultiplexing ........................... 16 2.7.2 Layer2asanAlternativetoTDM ...................... 18 2.8 Layer2:TheDataLayer..................................... 18 2.8.1 ConfigurethePiforLayer1andLayer2 ................ 20 2.9 Layer3:TheNetworkLayer ................................. 21 2.9.1 Layer3Addresses ................................... 21 2.10 UpperLayers.............................................. 22 2.11 Layer4:TheTransportLayer ................................ 23 xi