12081220+金雨鑫+Problem-10

Problem101.IPisaconnectionlessservice,sotheIPpacketiscalledthedatagram.Eachdatagramconsistsofaheaderfollowedbydataarea(payload).2.Adatagramheadcontainsinformation:sourceIPaddress(theoriginalsender)destinationIPaddress(theultimaterecipient)andafieldthatspecifiesthetypeofdatabeingcarriedinthepayload.3.IntheIPDatagramHeaderFormat,H.LENis4-bitheaderspecifiesthenumberof32-bitwordsintheheader.Ifnooptionsarepresent,thevalueis5.TOTALLENGTHisa16-bitintegerthatspecifiesthetotalnumberofbytesinthedatagram(includingboththeheaderandthedata).IDENTIFICATIONisa16-bitnumber(usuallysequential)assignedtothedatagram,whichisusedtogatherallfragmentsforreassemblytothedatagram.FLAGSisa3-bitfieldwithindividualbitsspecifyingwhetherthedatagramisafragment.FRAGMENTOFFSETisa13-bitfieldthatspecifieswhereintheoriginaldatagramthedatainthisfragmentbelongs,thevalueofthefieldismultipliedby8toobtainanoffset.TIMETOLIVE(TTL)isa8-bitintegerinitializedbytheoriginalsender.Itisdecrementedbyeachrouterthatprocessesthedatagram.Ifthevaluereacheszero(0),thedatagramisdiscardedandanerrormessageissentbacktothesource.TYPEis8-bitfieldthatspecifiesthetypeofthepayload.HEADERCHECKSUMis16-bitones-complementchecksumofheaderfields.IPOPTIONSisusedtocontrolroutinganddatagramprocessing.PADDINGmeansifoptionsdonotendona32-bitboundary,zerobitsofpaddingareaddedtomaketheheaderamultipleof32bits.4.WritetheTypeofIPDatagramHeaderforICMP-1,TCP-6,UDP-17,OSPF-89.5.ListsomefeaturesofIPv6:128bitIPaddresses、Baseheaderandextensionheaders、Supportforreal-timetraffic6.ForIPdelivery,Directdeliverywillhappenifthedestinationisonthesamenetwork.Indirectdeliverywillhappenthedestinationisnotonthesamenetwork7.IPdatagramforwardingmeanstoplacethedatagraminitsroutetoitsdestination.Forwardingrequiresahostoraroutertohavearoutingtable.8.Usuallyfordegaultrouting,Maskis0.0.0.0,anddestinationis0.0.0.0.9.Findtheroutingtable,OnUNIX/Linux,usingnetstatprogram.OnMSWindows,youcanalsouseroutePRINTprogram.10.Tomaketheselectionofanexthopefficient,anIProuterusesaforwardingtable(routingtable).Aforwardingtableisinitializedwhentherouterboots,andmustbeifthetopologychangesorhardwarefails.11.Forwardingtablecontainsasetofentries,eachspecifiesadestinationandthenexthopusedtoreachthatdestination.Eachdestinationinthetablecorrespondstoanetwork,thenumberofentriesinaforwardingtableisproportionaltothenumberofnetworksintheInternet.12.WhenanIPdatagramisencapsulatedinaframe,theentiredatagramisplacedinthepayloadareaofaframe.Softwareonthesendingcomputerassignstheframetypefield0x0800forIPdatagram.13.EachhardwaretechnologyspecifiesthemaximumamountofdatathataframecancarrynamedMaximumTransmissionUnit(MTU).14.AdatagrammustbesmallerorequaltothenetworkMTU,Fragmentationisrequiredotherwise.15.IPmakesabest-efforttodelivereachdatagram.IPdoesnotguaranteethatitwillhandleallproblems.ThefollowingproblemscanoccurinIPprotocol:Datagramduplication、Delayedorout-of-orderdelivery、Corruptionofdata、Datagramloss.