Routing table

Introduction

Incomputernetworks,aroutingtableorRouterSelectionInformationBase(RIB)isaspreadsheetstoredinarouterornetworkedcomputer(File)orclassdatabase.Theroutingtablestoresthepathtoaspecificnetworkaddress(insomecases,theroutingmetricofthepathisalsorecorded).Theroutingtablecontainstopologyinformationaroundthenetwork.Themaingoaloftheroutingtableistoimplementroutingprotocolsandstaticrouting.

Intheconstructionofmodernrouters,theroutingtabledoesnotdirectlyparticipateinthetransmissionofdatapackets,butisusedtogenerateasmallpointingtable.Thispointingtableonlycontainsthepreferentialpathofdatapackettransmissionselectedbytheroutingalgorithm.Tablesareusuallycompressedorcompiledaheadoftimeinordertooptimizehardwarestorageandsearch.

RoutingtableandFIB

EachrouterhasaroutingtableandFIB(ForwardInformationBase)table:theroutingtableisusedtomakeroutingdecisions,andFIBisusedtoforwardpackets.Therearethreetypesofroutesintheroutingtable:

(1)Routesdiscoveredbythelinklayerprotocol(thatis,directroutes)

(2)Staticroutes

(3)Routesdiscoveredbydynamicroutingprotocols.

EachforwardingentryintheFIBtableindicatesthatthepacketissenttoacertainnetworksegmentoracertainhostshouldbesentthroughthephysicalinterfaceoftherouter,andthenitcanreachthenextrouterofthepath,ornolongerpassthroughItistransmittedtothedestinationhostinthedirectlyconnectednetworkbyotherrouters.

Mainwork

Themainworkoftherouteristofindanoptimaltransmissionpathforeachdatapacketpassingthroughtherouter,andtoeffectivelytransmitthedatatothedestinationsite.Itcanbeseenthatthestrategyofselectingthebestpath,thatis,theroutingalgorithm,isthekeytotherouter.Inordertocompletethiswork,theroutingtable(RoutingTable)isstoredintherouterforvarioustransmissionpathrelateddataforroutingselection.Theinformationcontainedinthetabledeterminesthedataforwardingstrategy.Forexample,theroutingtableislikethemapweusuallyuse,markingvariousroutes.Theroutingtablestoresthesubnetlogoinformation,thenumberofroutersontheInternet,andthenameofthenextrouter.Theroutingtablecanbefixedlysetbythesystemadministrator,canalsobedynamicallymodifiedbythesystem,canbeautomaticallyadjustedbytherouter,orcontrolledbythehost.

1.Staticroutingtable

Thefixedroutingtablesetupbythesystemadministratorinadvanceiscalledastaticroutingtable.Itisgenerallypre-setaccordingtothenetworkconfigurationwhenthesystemisinstalled.ItdoesnotWillchangewithchangesinthenetworkstructureinthefuture.

2.Dynamicroutingtable

Dynamicroutingtableisaroutingtableautomaticallyadjustedbyroutersaccordingtotheoperatingconditionsofthenetworksystem.AccordingtothefunctionsprovidedbytheRoutingProtocol,therouterautomaticallylearnsandmemorizestheoperationofthenetwork,andautomaticallycalculatesthebestpathfordatatransmissionwhenneeded.

Routersusuallyrelyontheestablishedandmaintainedroutingtablestodecidehowtoforward.Theroutingtablecapacityreferstothelimitofthenumberofroutingtableentriescontainedintheroutingtable.BecauseroutersthatimplementtheBGPprotocolontheInternetusuallyhavehundredsofthousandsofroutingtableentries,thisprojectisalsoanimportantmanifestationoftherouter'scapabilities.

Theroutingtableentriesareasfollows:

First,thedestinationfieldofeachentryintheroutingtablecontainsthedestinationnetworkprefix.Secondly,eachitemhasanadditionalfieldandasubnetmaskforspecifyingthenumberofbitsofthenetworkprefix.Third,whenthenexthopfieldrepresentsarouter,thevalueofthenexthopfieldusestheIPaddressoftheroute.

Understandingthenetworkaddresses(ornetworkIDs)availableontheInternetcanhelpwithroutingdecisions.Thisknowledgeisobtainedfromadatabasecalledaroutingtable.Theroutingtableisaseriesofitemscalledrouting,whichcontainsinformationaboutthelocationofthenetworkIDoftheInternet.Theroutingtableisnotdedicatedtotherouter.Thehost(non-router)mayalsohavearoutingtableusedtodeterminetheoptimalroute.

Routingtableentry

Thecontentsoftheroutingtableinclude:

• destination:destinationaddress,usedtoidentifytheIPpacketDestinationaddressordestinationnetwork.

• mask:Netmask,togetherwiththedestinationaddress,itidentifiestheaddressofthenetworksegmentwherethedestinationhostorrouterislocated.

• pre:IdentifiesthepriorityofaddingtheroutetotheIProutingtable.Theremaybemultipleroutestoadestination,buttheexistenceofpriorityallowsthemtochoosearoutewithahigherprioritytouse.

• cost:routecost.Whenmultipleroutestoadestinationhavethesamepriority,theonewiththesmallestroutecostwillbecometheoptimalroute.

• interface:outputinterface,indicatingwhichinterfacetheIPpacketwillbeforwardedfrom.

• nexthop:nexthopIPaddress,indicatingthenextroutertheIPpacketpassesthrough.

Classification

1.Staticroutingtable

Staticroutingisafixedroutemanuallyconfiguredbytheadministratorintherouter.Routingclearlyspecifiesthepaththatapacketmusttaketoreachitsdestination,andstaticroutingwillnotchangeunlessthenetworkadministratorintervenes.Staticroutingcannotrespondtochangesinthenetwork,soitisgenerallysaidthatstaticroutingisusedfornetworkswithasmallnetworkscaleandrelativelyfixedtopology.

Features:

1,itallowsprecisecontrolofroutingbehavior

2,reducesnetworktraffic

3,Itisone-way

4.Simpleconfiguration

2.Dynamicroutingtable

Dynamicroutingtablereferstotheautomaticestablishmentofroutingtablebydynamicroutingprotocol(suchasRIP),Whenyouremoveaconnection,itwillautomaticallyremoveitsrouting.Eachinterfaceoftheroutercorrespondstoadifferentnetwork,andthetwoendpointIPsconnectingthetworoutersshouldbelongtothesamenetwork.WhensettingtheIPaddress,iftheotherportoftherouteralreadyhasthisnetwork,itwillpromptthatthereisthisnetworkanddisplaythecorrespondingport.

Features:

1.Lessworkloadwhenaddingordeletingnodes

2.Networktopologychanges,protocolautomaticadjustment

3.ConfigurationNoteasytomakemistakes

4,goodnetworkscalability

5,needtooccupyrouterresources