Routing information protocol

Introduction

TheroutinginformationprotocolRIP(RoutingInformationProtocol)isaroutingprotocolbasedonthedistancevectoralgorithm,whichusesthenumberofhopsasthemeasurementstandard.Thebandwidth,configuration,andmanagementrequirementsarerelativelylow,anditismainlysuitableforsmaller-scalenetworks.

Version

Version:RIPv1,RIPv2andRIPng,thefirsttwoareusedforIPv4,andRIPngisusedforIPv6.

Amongthem,RIPv1isaclassfulroutingprotocol,whichdoesnotsupportVLSMandCIDR;sendsmessagesintheformofbroadcast;doesnotsupportauthentication.RIPv2isaclasslessroutingprotocolthatsupportsVLSM,routeaggregationandCIDR;supportssendingmessagesbybroadcastormulticast(224.0.0.9);supportsplaintextauthenticationandMD5ciphertextauthentication.

DevelopmentHistory

XeroxandtheUniversityofCalifornia,BerkeleybothdevelopedearlyversionsofRIPintheearly1980s.

RFC1058in1988explainedtheRIPprotocol,whichwaslatercalledRIPv1.

In1998,theIETFreleasedtheformalstandardRFC2453,animprovedversionofRIP,namelyRIPv2:supportsubnetmaskinformation;supportroutingobjectflags;supportroutingupdateauthentication.

In1997,theIETFlaunchedthenext-generationRIPprotocol-RIPng'sproposedstandardRFC2080.

Workingprinciple

(1)Routeestablishment

AftertherouterrunsRIP,itwillfirstsendaroutingupdaterequest,andtherouterthatreceivestherequestwillsenditsownRIPTheroutingresponds;afterthenetworkisstable,therouterwillperiodicallysendroutingupdateinformation.

(2)Calculationofdistancevector

TheunitofRIPmeasurementisthenumberofhops,anditsunitis1,whichmeansthatthecostofeachlinkis1regardlessofthechainRIPallowsupto15hopsforfactorssuchastheactualbandwidthanddelayoftheroad.

RIPusesmetricstoindicatethedistancebetweenitandallknowndestinations.

WhenaRIPupdatemessagearrives,thereceiverroutercompareseachiteminitsownRIProutingtable,andcorrectsitsownRIProutingtableaccordingtothedistancevectorroutingalgorithm.

(3)Timer

Periodicupdatetimer:usedtostimulatetheupdateoftheRIProuterroutingtable,eachRIPnodehasonlyoneupdatetimer,setto30s.Every30s,therouterwillbroadcastitsroutingtableinformationtoitsneighbors.ThetimerofeachRIProuterisindependentofotherroutersinthenetwork,soitisveryunlikelythattheywillbroadcastatthesametime.

Timeouttimer:usedtodeterminewhetherarouteisavailable.Eachroutehasatimeouttimer,whichissetto180s.Whenarouteisactivatedorupdated,thetimerisinitialized.Ifnoupdateonthatrouteisreceivedwithin180s,theroutewillbeinvalidated.

Cleartimer:usedtodeterminewhethertocleararoute.Eachroutehasacleartimer,whichissetto120s.Whentherouterrecognizesthatacertainrouteisinvalid,itinitializesacleartimer,andifithasnotreceivedtheupdateofthisroutewithin120s,itdeletestheroutefromtheroutingtable.

Delaytimer:Arandomdelaytimersettoavoidtriggeringtheupdatetocauseabroadcaststorm.Thedelaytimeis1~5s.

(4)Loop

Whenthenetworkfails,theRIPnetworkmayhavearoutingloop.Thegenerationofloopscanbeavoidedbytechniquessuchassplithorizon,poisonreversal,triggerupdate,andsuppressiontime.

Disadvantages

Because15hopsisthemaximumvalue,RIPcanonlybeappliedtosmall-scalenetworks;

Slowconvergencespeed;

AccordingtoTherouteselectedbythehopcountisnotnecessarilytheoptimalroute.