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1、网络子网掩码详解(局域网络分割)（Detaileddescriptionofnetworksubnetmask(localnetworkpartition)）SubnetmaskoverviewTheconceptof1.subnetmaskSubnetmaskisa32bitaddress,whichisusedtoshieldpartoftheIPaddresstodistinguishnetworkidentificationandhostidentification,andtoexplainwhethertheIPaddressisontheLANorontheremoten
2、etwork.2.determinesubnetmasknumberThenumberofbitsusedforsubnetmasksdependsonthenumberofpossiblesubnetsandthenumberofhostspersubnet.Beforethesubnetmaskisdefined,thenumberofsubnetsandthenumberofhostsmustbeknown.Thestepsfordefiningsubnetmasksare:Aanddeterminewhichgroupaddressesareusedbyus.Forexamp
3、le,weapplyforthenetworknumberis"210.73.a.b",thenetworkaddressisCclassIPaddress,thenetworkidentifieris"210.73",thehostidentifiesas"A.B"".Bdefinessubnetmasksaccordingtothenumberofsubnetsweneednowandthenumberofsubnetsthatmaybeextendedinthefuture.Forexample,weneed12subnetsnow,andwemayneed16inthefut
4、ure.Thesubnetmaskisdeterminedbythefirstfourbytesofthirdbytes.Thefirstfourbitsareall"1",thatis,thethirdbyteis"11110000",whichwecallthenewbinarysubnetmasktemporarily.C,thecorrespondinginitialnetworkallbitsaresetto"1",thefirsttwobytesaresetto"1",fourthbytesaresetto"0",thenthesubnetmaskofthediscont
5、inuousbinaryform:"11111111.11111111.11110000.00000000"D,convertthisnumberintodiscontinuousdecimalform:"255.255.240.0""Thisnumberisthesubnetmaskofthenetwork.Annotationof3.IPmaskAnnotationmethodofAandsubnetwithoutsubnetTheIPaddressofthesubnetcanbewrittenasamaskwiththehostnumberof0.SuchasIPaddress
6、210.73.140.5,mask255.255.255.0,youcanalsodefaultmask,onlywriteIPaddress.TaggingmethodofBandsubnetWhenyouhaveasubnet,youmustmatchthetwo.TakeCclassaddressasanexample.Thefirst3bytesinthe1.IPaddressofthenetworknumber,afterabytebothshowthenetworknumber,hostnumberanddescription,alsoshowsthatthetwoIPa
7、ddressesbelongtoanetwork.Iftheybelongtothesamenetworkinterval,theinformationexchangebetweenthesetwoaddresseswillnotpassthroughtherouter.Ifthenetworkisnotthesameinterval,thatis,subnetnumberisdifferent,thetwoaddressesofinformationex
