互联网2013会上网懂网络

IntroductiontoComputerSystems24thLecture,Dec.12,2013XiangqunChen，JunlinLuChapter11NetworkingHowtosetupanetworkconnectionandawebserverbyprogramming?WhatiscomputernetworkInternetandaclient-serverHostandcomputerNetworkGlobalIPProgrammer’sviewofEvolutionofInternet=web上网：Hao123BaiduInternet=client-AClient-Server4.Client

Clientsends3.Serversends

Note:clientsandserversareprocessesrunningonhosts(canbethesameordifferenthosts)Mostnetworkapplicationsarebasedontheclient-serverAserverprocessandoneormoreclientServermanagessomeServerprovidesservicebymanipulatingresourceforServeractivatedbyrequestfromclient(vendingmachineNetworkforcommunicationbetween通信、服务socialnetworkcomputerImplementationofhumansocietyindigital……Internetandaclient-serverHostandcomputerNetworkGlobalIPProgrammer’sviewofEvolutionofNetworkComputerAnetworkisahierarchicalsystemofboxesandwiresorganizedbygeographicalproximitySAN(SystemAreaNetwork)spansclusterormachineSwitchedEthernet,QuadricsQSW,LAN(LocalAreaNetwork)spansabuildingorEthernetismostprominentWAN(WideAreaNetwork)spanscountryorAninternetwork(internet)isaninterconnectedsetofTheGlobalIPInternet(uppercase“I”)isthemostfamousexampleofaninternet(lowercase“i”)Let’sseehowaninternetisbuiltfromthegroundLowestLevel:Ethernet100

100Ethernetsegmentconsistsofacollectionofhostsconnectedbywires(twistedpairs)toahubLocal:SpansroomorfloorinaOperations：HubslavishlycopieseachbitfromeachporttoeveryotherportBridges/routersbecamecheapenoughtoreplacetheNextLevel:BridgedEthernet 100X1001100Y100 Spansbuildingor BridgescleverlylearnwhichhostsarereachablefromwhichportsandthenselectivelycopyframesfromporttoportConceptualViewofForsimplicity,hubs,bridges,andwiresareoftenshownasacollectionofhostsattachedtoasinglewire:NextLevel:MultipleincompatibleLANscanbephysicallyconnectedbyspecializedcomputerscalledroutersTheconnectednetworksarecalledan LAN

LANLAN1andLAN2mightbecompletelydifferent,totallyincompatible(e.g.,EthernetandWifi,802.11*,T1-links,DSL,LogicalStructureofanSendpacketsfromsourcetodestinationbyhoppingthroughnetworksInternetandaclient-serverHostandcomputerNetworkGlobalIPProgrammer’sviewofEvolutionofWhatisaPre-agreedSmile=开心Cry=悲伤点头=yes 摇头=noHumanWhat'stheSpecificmsgsSpecificactionstakenwhenmsgsreceived,orothereventsTheNotionofaninternetQuestion:HowisitpossibletosendbitsacrossincompatibleLANsandWANs?protocolsoftwarerunningoneachhostandsmoothsoutthedifferencesbetweenthedifferent邮局（因为邮局有统一的协议、规则Implementsaninternetprotocol(i.e.,setofgovernshowhostsandroutersshouldcooperatewhentransferdatafromnetworktonetworkTCP/IPistheprotocolfortheglobalIPWhatDoesaninternetProtocolProvidesanamingscheme（即设定地址AninternetprotocoldefinesauniformformatforhostEachhost(androuter)isassignedatleastoneofinternetaddressesthatuniquelyidentifiesProvidesadeliverymechanism（如邮政投Aninternetprotocoldefinesastandardtransferunittobedelivered(packet)PacketconsistsofheaderandHeader:containsinfosuchaspacketsize,sourceanddestinationaddressesPayload:containsdatabitssentfromsourceTransferringDataOveran

Host Host

LAN1

LAN2

FH:LANframeheader

WeareglossingoveranumberofimportantWhatifdifferentnetworkshavedifferentmaximumframesizes?(segmentation)数据包大小不同怎么办？Howdoroutersknowwheretoforwardframes?路由器怎么知道HowareroutersinformedwhenthenetworktopologyThese(andother)questionsareaddressedbytheareaofsystemsknownascomputernetworkingInternetandaclient-serverHostandcomputerNetworkGlobalIPProgrammer’sviewofEvolutionofGlobalIPMostfamousexampleofanBasedontheTCP/IPprotocolIP(Internetprotocol)

Providesbasicnamingschemeandunreliabledeliveryofpackets(datagrams)fromhost-to-UsesIPtoprovideunreliabledatagramdelivery

UsesIPtoprovidereliablebytestreamsfromprocess-to-overAccessedviaamixofUnixfileI/OandfunctionsfromsocketsinterfaceHardwareandSoftwareofanInternet

BasicInternetInternetbackbone:collectionofrouters(nationwideorworldwide)connectedbyhigh-InternetExchangePoints(IXP):routerthatconnectsmultiplebackbones(oftenreferredtoasAlsocalledNetworkAccessPointsRegionalnetworks:smallerbackbonesthatcoversmallergeographical(e.g.,citiesorPointofpresencePOP):machinethatisconnectedtotheInternetServiceProvidersISPs):providedial-upordirectaccesstoInternetConnectionoftenbypass

Regional Big

ISP(for Small Pgh DCInternetandaclient-serverHostandcomputerNetworkGlobalIPProgrammer’sviewofEvolutionofAProgrammer’sViewoftheHostsaremappedtoasetof32-bitIPThesetofIPaddressesismappedtoasetofidentifierscalledInternetdomainnames79ismappedtoAprocessononeInternethostcancommunicatewithaprocessonanotherInternethostoveraconnectionIP32-bitIPaddressesarestoredinanIPaddressIPaddressesarealwaysstoredinmemoryinnetworkbyteorder(big-endianbyteorder)Trueingeneralforanyintegertransferredinapacketheaderfromonemachinetoanother.E.g.,theportnumberusedtoidentifyanInternet/*/*Internetaddressstructure*/structin_addr{unsignedints_addr;/*networkbyteorder(big-endian)Usefulnetworkbyte-orderconversionfunctions(“l”=32bits,“s”=16htonl:convertuint32_tfromhosttonetworkbyteorderhtons:convertuint16_tfromhosttonetworkbyteorderntohl:convertuint32_tfromnetworktohostbyteorderntohs:convertuint16_tfromnetworktohostbyteorderDottedDecimalByconvention,eachbyteina32-bitIPaddressisrepresentedbyitsdecimalvalueandseparatedbyaperiodIPaddress16进制100x8002C2F2=FunctionsforconvertingbetweenbinaryIPaddressesanddotteddecimalstrings:inet_ntoa:IPaddressinnetworkbyteorder→dotteddecimalinet_aton:dotteddecimalstring→IPaddressinnetworkbyte“n”denotesnetwork“a”denotesapplicationIPAddressIP(V4)Addressspacedividedinto0NetHost10NetHost0NetHost10NetHost110NetHost1110Reservedfor1111ClassClassBClassCClassDClassENetworkIDWritteninformn=numberofbitsinhostE.g.,CMUwrittenas/16,北大BClassBUn-routed(private)IP InternetDomain First-leveldomain Second-leveldomain

Third-leveldomain

DomainNamingServiceTheInternetmaintainsamappingbetweenIPaddressesanddomainnamesinahugeworldwidedistributeddatabasecalledDNS域名服务器Conceptually,programmerscanviewtheDNSdatabaseasacollectionmillionsofhostentry/*/*DNShostentrystructure*/structhostent{/*officialdomainnameofhost**h_aliases;/*null-terminatedarrayofdomainnames/*hostaddresstype(AF_INET)/*lengthofanaddress,inbytes**h_addr_list;/*null-terminatedarrayofin_addrstructsFunctionsforretrievinghostentriesfromgethostbyname:querykeyisaDNSdomaingethostbyaddr:querykeyisanIPPropertiesofDNSHostEachhostentryisanequivalenceclassofdomainnamesandIPaddresses每个主机记录=若干名字+地址EachhosthasalocallydefineddomainnamewhichalwaysmapstotheloopbackaddressDifferentkindsofmappingsareSimplecase:one-to-onemappingbetweendomainnameandIPmapstoMultipledomainnamesmappedtothesameIPandbothmaptoMultipledomainnamesmappedtomultipleIPmapstomultipleIPSomevaliddomainnamesdon’tmaptoanyIPAProgramThatQueriesintmain(intargc,char**argv){/*argv[1]isadomainname*/char**pp; /*ordotteddecimalIPaddr*/structin_addraddr;structhostent*hostp;/*pointertoaDNShostentrystructureif(inet_aton(argv[1],&addr)!=hostp=Gethostbyaddr((constchar*)&addr, 42tohostp=printf("officialhostname:%s\n",hostp-//printhostnamefor(pp=hostp->h_aliases;*pp!=NULL;pp++)printf("alias:%s\n",*pp);//printallaliasfor(pp=hostp->h_addr_list;*pp!=NULL;{addr.s_addr=((structin_addr*)*pp)->s_addr;printf("address:%s\n",inet_ntoa(addr));}//printall}UsingDNSlinux>./dnsofficialhostname:address0linux>./dnsofficialhostname:ANGELSHARK.ICS.CS.CMU.EDUaddress:1linux>./dnsofficialhostname:QueryingDomainInformationGroper(dig)providesascriptablecommandlineinterfacetoDNSlinux>linux>dig+linux>dig+short-x1linux>dig+InternetClientsandserverscommunicatebysendingstreamsofbytesoverconnections:什么是互联网连接？AsocketisanendpointofaSocketaddressisanIPaddress:port

IPAportisa16-bitintegerthatidentifiesaEphemeralport:AssignedautomaticallyandtemporarilyonclientwhenclientmakesaconnectionrequestWell-knownport:Associatedwithsomeserviceprovidedbyaserver(e.g.,port80isassociatedwithWebservers)Aconnectionisuniquelyidentifiedbythesocketaddressesofitsendpoints(socketpair)PuttingitallAnatomyofanInternetClientsoc