Case Studies in Transitioning Routing Protocols

1©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicCaseStudiesinTransitioningRoutingProtocolsRST-33642©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTransitioningRoutingProtocols•CutoverAtOnce•SplittingtheProblem•Redistribution•OtherTechniques•Summary3©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTransitioningRoutingProtocols•ThereisaquickandeasywaytotransitionfromoneprotocolanotherwithoutanynetworkdowntimePerhaps—Ifyoudiscoverit,letmeknow•It’simpossibletotransitionfromoneroutingprotocoltoanotherinareallylargenetworkIt’salmostalwaysdifficult,butneverimpossible4©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTransitioningRoutingProtocols•It’sneverworththetroubleofswitchingroutingprotocolsThatdepends....Wouldthecostbenefitsoutweighthetransitioncosts?DifferentialsinoverallequipmentcostsinthefutureConvergencespeedsonspecificnetworktopologiesOtherfactors....Yousometimesdon’thaveachoice,suchaswhenmergingtwonetworks5©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTransitioningRoutingProtocols•Whatreasonshaveweheardinthefieldforswitchingroutingprotocols?“Wewantfasterconvergence...”Generallyconvergenceisamatterofdesign,ratherthanprotocol“Ournetworkdesignishubandspoke,soitfitsbetterforEIGRP....”Can’targuewiththisone....☺“Wewantastandardsbasedprotocol....”What,soyoucaninstallsome“other”vendor’sequipment?Areyouinsane????☺“We’reallstudyingforourCCIE’s,andneedexposuretootherprotocols....”6©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicCutoverAtOnce7©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicCutoverAtOnce•TheWrongWay:ACaseStudy•LessonsLearned•SecondTry:TheHardWay8©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTheWrongWay:ACaseStudy•Networkdesign900routersonasinglecampusComplexpartialmeshdesignwith6“anchorpoints”or“hubs”onthemeshThisisahardproblem!•Easysolution:“We’llwriteascript!”9©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTheWrongWay:ACaseStudy•ExistingRoutingMultipleEIGRPandIGRPprocessesscatteredthroughoutthenetworkRedistributionbetweenprocessesatvariouspoints•Thisisahardproblem!•Easysolution:“We’llwriteascript!”☺10©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTheWrongWay:ACaseStudy•Thescriptstartsatthehubrouter,and:TelnetstoeachneighborRemovestheoldroutingprotocolConfiguresthenewroutingprotocolRecursesateachleveltocovertheentirenetwork•Theresult?Asixtoeighthournetworkfailure!11©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTheWrongWay:ACaseStudy•Thescriptstartedclose,andworkedtotheedgeofthenetworkThescriptreliedonroutingtoreachroutersasitworkedfartheroutinthenetworkBut,thescriptischangingtheroutingit’sdependingonSawingoffthelimbyou’resittingoncomestomind....WhatWentWrong?12©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicTheWrongWay:ACaseStudy•ThescriptworkedtoofastThenetworkcouldn’tsettlebetweenchangesThechangeratebuiltuntilthenetworkbuiltapositivefeedbackloop,andwouldn’tconverge•Thescriptwasn’tatomicIfitwascutoffinthemiddleofsomechange,thefinalresultwasapartialconversionThisaddedtonetworkinstabilityWhatWentWrong?13©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicLessonsLearned•Don’tcountonroutedreachabilitywhileyouareswitchingtheroutingprotocolStartfromoneendofthenetworkTelnettotheotherendhopbyhop,removingroutingateachstepApplynewroutingprotocolattherouterfarthestawayBackout,applyingnewroutingprotocolhopbyhopTelnetTelnetTelnetRemoveroutingRemoveroutingConfigureroutingConfigureroutingRemoveroutingConfigureroutingRemoveroutingConfigureroutingBreakBeforeMake14©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicLessonsLearned•Ifthenetworkdestabilizes,takeabreak•Ateachrouter,waituntilthenetworkhasconvergedbeforemovingtothenextrouterWhenyouconfigureroutingonagivenrouter,waituntiltheroutingprotocolisquiescentForinstance,forEIGRP,lookatshowipeigrpneighbors,andwaituntiltheQCountis0onallinterfaces•ThistechniqueshouldbeusedwhetherconvertingmanuallyorwhenusingascriptTelnetTelnetTelnetRemoveroutingRemoveroutingRemoveroutingRemoveroutingConfigureroutingConfigureroutingConfigureroutingConfigureroutingWaitforconvergenceWaitforconvergenceWaitforconvergenceWaitforconvergenceWatchforInstability15©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicLessonsLearned•Iftheprocessstallsorfails,eachdeviceshouldbeleftcompletelyinaknownstateThereshouldbenochanceofpartialconfigurations•OnlyoneofthreestatesshouldbepossibleTheoldroutingprotocoliscompletelyconfiguredNoroutingisconfiguredThenewroutingprotocoliscompletelyconfiguredMaketheProcessAtomic16©2005CiscoSystems,Inc.Allrightsreserved.RST-336412700_05_2006_x2CiscoPublicLessonsLearned•CreateeachnewroutingconfigurationinalocallyaccessiblefileRemembernottocountonreachingaserver•AteachrouterOpen