internet protocols

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1、InternetProtocolsBackgroundTheInternetprotocolsaretheworld'smostpopularopen-system(nonproprietary)protocolsuitebecausetheycanbeusedtocommunicateacrossanysetofinterconnectednetworksandareequallywellsuitedforLANandWANcommunications.TheInternetprotocolsconsistofasuiteofcom

2、municationprotocols,ofwhichthetwobestknownaretheTransmissionControlProtocol(TCP)andtheInternetProtocol(IP).TheInternetprotocolsuitenotonlyincludeslower-layerprotocols(suchasTCPandIP),butitalsospecifiescommonapplicationssuchaselectronicmail,terminalemulation,andfiletrans

3、fer.ThischapterprovidesabroadintroductiontospecificationsthatcomprisetheInternetprotocols.DiscussionsincludeIPaddressingandkeyupper-layerprotocolsusedintheInternet.SpecificroutingprotocolsareaddressedindividuallyinPart6,RoutingProtocols.Internetprotocolswerefirstdevelop

4、edinthemid-1970s,whentheDefenseAdvancedResearchProjectsAgency(DARPA)becameinterestedinestablishingapacket-switchednetworkthatwouldfacilitatecommunicationbetweendissimilarcomputersystemsatresearchinstitutions.Withthegoalofheterogeneousconnectivityinmind,DARPAfundedresear

5、chbyStanfordUniversityandBolt,Beranek,andNewman(BBN).TheresultofthisdevelopmenteffortwastheInternetprotocolsuite,completedinthelate1970s.TCP/IPlaterwasincludedwithBerkeleySoftwareDistribution(BSD)UNIXandhassincebecomethefoundationonwhichtheInternetandtheWorldWideWeb(WWW

6、)arebased.DocumentationoftheInternetprotocols(includingneworrevisedprotocols)andpoliciesarespecifiedintechnicalreportscalledRequestForComments(RFCs),whicharepublishedandthenreviewedandanalyzedbytheInternetcommunity.ProtocolrefinementsarepublishedinthenewRFCs.Toillustrat

7、ethescopeoftheInternetprotocols,Figure30-1mapsmanyoftheprotocolsoftheInternetprotocolsuiteandtheircorrespondingOSIlayers.ThischapteraddressesthebasicelementsandoperationsoftheseandotherkeyInternetprotocols.Figure 30-1:InternetprotocolsspanthecompleterangeofOSImodellayer

8、s.InternetProtocol(IP)TheInternetProtocol(IP)isanetwork-layer(Layer3)protocolthatcontainsaddressinginformation