计算机网络专业译文关于IPv6.docx

计算机网络专业译文关于IPv6.docx

《计算机网络专业译文关于IPv6.docx》由会员分享，可在线阅读，更多相关《计算机网络专业译文关于IPv6.docx（18页珍藏版）》请在冰豆网上搜索。

计算机网络专业译文关于IPv6

专业译文

原文：

《CiscoCertifiedNetworkAssociateStudyGuide.SixthEdition》的第740-747页

（作者：

ToddLammle出版社：

WileyPublishing,Inc.）

英语原文：

Ihopeyou'rereadytolearnaboutthenutsandboltsofInternetProtocolversion6（IPv6）,becauseyou'regoingtogettherubonitinthischapter!

YoushouldhaveasolidholdonIPv4bynow,butifyouthinkyoucouldusearefresher,justpagebacktoChapter3,"Subnetting,VariableLengthSubnetMasks（VLSMs）,andTroubleshootingTCP/IP."Andifyou'renotcrystalclearontheaddressproblemsinherenttoIPv4,youreallyshouldreviewChapter11,"NetworkAddressTranslation（NAT）”

PeoplerefertoIPv6as"thenext-generationInternetprotocol,"anditwasoriginallycreatedastheanswertoIPv4'sinevitable,loomingaddress-exhaustioncrisis.Thoughyou'veprobablyheardathingortwoaboutIPv6already,ithasbeenimprovedevenfurtherinthequesttobringustheflexibility,efficiency,capability,andoptimizedfunctionalitythatcantrulymeetoureverincreasingneeds.Thecapacityofitspredecessor,IPv4,palesincomparison-andthat'sthereasonitwilleventuallyfadeintohistorycompletely.

TheIPv6headerandaddressstructurehasbeencompletelyoverhauled,andmanyofthefeaturesthatwerebasicallyjustafterthoughtsandaddendumsinIPv4arenowincludedasfull-blownstandardsinIPv6.It'sseriouslywellequipped,poised,andreadytomanagethemind-blowingdemandsoftheInternettocome.

Ipromise-really-tomakethischapterprettypainless.Infact,youmightevenfindyourselfactuallyenjoyingit-Idefinitelydid!

BecauseIPv6issocomplexyetelegant,innovativeandchock-fulloffeatures,itfascinatesmelikesomeweirdcombinationofabrand-newLamborghiniandarivetingfuturisticnovel.Hopefullyyou'llexperiencethischapterasthecoolridethatIdidwritingit!

WhyDoWeNeedIPv6?

Well,theshortansweris,becauseweneedtocommunicate,andourcurrentsystemisn'treallycuttingitanymore-kindoflikehowthePonyExpresscan'tcompetewithairmail.Justlookathowmuchtimeandeffortwe'veinvestedincomingupwithslicknewwaystoconservebandwidthandIPaddresses.We'veevencomeupwithVariableLengthSubnetMasks（VLSMs）inourstruggletoovercometheworseningaddressdroughtIt'sreality-thenumberofpeopleanddevicesthatconnecttonetworksincreaseseachandeveryday.That'snotabadthingatall-we'refindingnewandexcitingwaystocommunicatetomorepeopleallthetime,andthat'sagoodthing.Infact,it'sabasichumanneed.Buttheforecastisn'texactlyblueskiesandsunshinebecause,asIalludedtointhischapter'sintroduction,IPv4,uponwhichourabilitytocommunicateispresentlydependent,isgoingtorunoutofaddressesforustouse.IPv4hasonlyabout4.3billionaddressesavailable-intheory,andweknowthatwedon'tevengettouseallofthose.Therereallyareonlyabout250millionaddressesthatcanbeassignedtodevices.Sure,theuseofClasslessInter-DomainRouting（CIDR）andNetworkAddressTranslation（NAT）hashelpedtoextendtheinevitabledearthofaddresses,butwewillrunoutofthem,andit'sgoingtohappenwithinafewyears.Chinaisbarelyonline,andweknowthere'sahugepopulationofpeopleandcorporationstherethatsurelywanttobe.Therearealotofreportsthatgiveusallkindsofnumbers,butallyoureallyneedtothinkabouttoconvinceyourselfthatI'mnotjustbeinganalarmististhefactthatthereareabout6.5billionpeopleintheworldtoday,andit'sestimatedthatjustover10percentofthatpopulationisconnectedtotheInternet-wow!

ThatstatisticisbasicallyscreamingatustheuglytruththatbasedonIPv4'scapacity,everypersoncan'tevenhaveacomputer-letalonealltheotherdevicesweusewiththem.Ihavemorethanonecomputer,andit'sprettylikelyyoudotoo.AndI'mnotevenincludinginthemixphones,laptops,gameconsoles,faxmachines,routers,switches,andamotherlodeofotherdevicesweuseeveryday!

SoIthinkI'vemadeitprettyclearthatwe'vegottodosomethingbeforewerunoutofaddressesandlosetheabilitytoconnectwitheachotherasweknowit.Andthat"something"justhappenstobeimplementingIPv6.

TheBenefitsandUsesofIPv6

Sowhat'ssofabulousaboutIPv6?

Isitreallytheanswertoourcomingdilemma?

IsitreallyworthittoupgradefromIPv4?

Allgoodquestions-youmayeventhinkofafewmore.Ofcourse,there'sgoingtobethatgroupofpeoplewiththetime-testedandwell-known"resistancetochangesyndrome,"butdon'tlistentothem.Ifwehaddonethatyearsago,we'dstillbewaitingweeks,evenmonthsforourmailtoarriveviahorseback.Instead,justknowthattheanswerisaresoundingYES!

NotonlydoesIPv6giveuslotsofaddresses（3.4x1038=definitelyenough）,buttherearemanyotherfeaturesbuiltintothisversionthatmakeitwellworththecost,time,andeffortrequiredtomigratetoit.LaterinthechapterI'lltalkaboutallthateffortinthesectioncalled"MigratingtoIPv6."Init,I'llcoversomeofthetransitiontypesrequiredtomovefromversion4toversion6,andIpromiseyou'lldiscoverthatthehugebenefitsofmigratingwillvastlyoutweighanyassociatedcons.

Today'snetworks,aswellastheInternet,haveatonofunforeseenrequirementsthatsimplywerenotconsiderationswhenIPv4wascreated.We'vetriedtocompensatewithacollectionofadd-onsthatcanactuallymakeimplementingthemmoredifficultthantheywouldbeiftheywererequiredbyastandard.Bydefault,IPv6hasimproveduponandincludedmanyofthosefeaturesasstandardandmandatory.OneofthesesweetnewstandardsisIPSec-afeaturethatprovidesend-to-endsecuritythatI'llcoveriliChapter14,"WideAreaNetworks."Anotherlittlebeautyisknownasmobility,andasitsnamesuggests,itallowsadevicetoroamfromonenetworktoanotherwithoutdroppingconnections.

Butit'stheefficiencyfeaturesthatarereallygoingtorockthehouse!

Forstarters,theheaderinanIPv6packethavehalfthefields,andtheyarealignedto64bits,whichgivesussomeseriouslysouped-upprocessingspeed-comparedtoIPv4,lookupshappenatlightspeed!

MostoftheinformationthatusedtobeboundintotheIPv4headerwastakenout,andnowyoucanchoosetoputit,orpartsofit,backintotheheaderintheformofoptionalextensionheadersthatfollowthebasicheaderfields.

Andofcoursethere'sthatwholenewuniverseofaddresses（3.4x1038）wetalkedaboutalready.Butwheredidwegetthem?

DidthatCrissAngel-Mindfreakdudejustshowupand,Blammo?

Imean,thathugeproliferationofaddresseshadtocomefromsomewhere!

WellitjustsohappensthatIPv6givesusasubstantiallylargeraddressspace,meaningtheaddressisawholelotbigger-fourtimesbiggerasamatteroffact!

AnIPv6addressisactually128bitsinlength,andnoworries-I'mgoingtobreakdowntheaddresspiecebypieceandshowyouexactlywhatitlookslikecomingupinthesection"IPv6AddressingandExpressions."Fornow,letmejustsaythatallthatadditionalroompermitsmorelevelsofhierarchyinsidetheaddressspaceandamoreflexibleaddressarchitecture.Italsomakesroutingmuchmoreefficientandscalablebecausetheaddressescanbeaggregatedalotmoreeffectively.AndIPv6alsoallowsmultipleaddressesforhostsandnetworks.Thisisespeciallyimportantforenterprisesjonesingforavailability.Plus,thenewversionofIPnowincludesanexpandeduseofmulticastcommunication（onedevicesendingtomanyhostsortoaselectgroup）,whichwillalsojoinintoboostefficiencyonnetworksbecausecommunicationswillbemorespecific.

IPv4usesbroadcastsveryprolifically,causingabunchofproblems,theworstofwhichisofcoursethedreadedbroadcaststorm-anuncontrolleddelugeofforwardedbroadcasttrafficthatcanbringanentirenetworktoitskneesanddevoureverylastbitofbandwidth.Anothernastythingaboutbroadcasttrafficisthatitinterruptseachandeverydeviceonthenetwork.Whenabroadcastissentout,everymachinehastostopwhatit'sdoingandrespondtothetrafficwhetherthebroadcastismeantforitornot.

Butsmileeveryone:

ThereisnosuchthingasabroadcastinIPv6becauseitusesmulticasttrafficinstead.Andtherearetwoothertypesofcommunicationaswell:

unicast,whichisthesameasitisinIPv4,andanewtypecalledanycast.Anycastcommunicationallowsthesameaddresstobeplacedonmorethanonedevicesothatwhentrafficissenttoonedeviceaddressedinthisway,itisroutedtothenearesthostthatsharesthesameaddress.Thisisjustthebeginning-we'llgetmoreintothevarioustypesofcommunicationinthesectioncalled"AddressTypes”

IPv6AddressingandExpressions

JustasunderstandinghowIPaddressesarestructuredandusediscriticalwithIPv4addressing,it'salsovitalwhenitcomestoIPv6.You'vealreadyreadaboutthefactthatat128bits,anIPv6addressismuchlargerthananIPv4address.Becauseofthis,aswellasthenewwaystheaddressesmanage.Butcanbeused,you'veprobablyguessedthatIPv6willbemorecomplicatedtonoworries!

AsIsaid,I'llbreakdownthebasicsandshowyouwhattheaddresslookslike,howyoucanwriteit,andwhatmanyofitscommonusesare.It'sgoingtobealittleweirdatfirst,butbeforeyouknowit,you'llhaveitnailed!

Solet'stakealookatFigure13.1,whichhasasampleIPv6addressbrokendownintosections.

FIGURE13.1IPv6addressexample

Soasyoucannowsee,theaddressistrulymuchlarger-butwhatelseisdifferent?

Well,first,noticethatithaseightgroupsofnumbersinsteadoffourandalsothatthosegroupsareseparatedbycolonsinsteadofperiods.A