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1 AdvancedNetworkManagementFunctionalities throughtheuseofmobilesoftwareagents 1DipartimentodiMatematica,UniversitadiMessina C.daPapardo-SalitaSperone,98166Messina-Italy AntonioPuliato1,OrazioTomarchio2 2IstitutodiInformaticaeTelecomunicazioni,UniversitadiCatania VialeA.Doria6,95025Catania-Italy tributedoverthenetwork.consequently,managementstrategiesarebe- comingofcrucialimportanceinordertoguaranteeaneectivecontrolof thesystem,bothintermsofperformanceandreliability.mobileagents Abstract.Computingpowerandstoragespacearemoreandmoredis- plementationbasedonourmobileagentplatformcalledmap. howtotakeadvantageofthistechnologyanddescribeaprototypeim- representachallengingapproachtoprovideadvancednetworkmanagetralizedandactivemonitoringofthesystem.inthispaperwediscusmentfunctionalities,duetothepossibilitytoeasilyimplementadecen- 1Introduction Keywords:networkmanagement,mobileagents,SNMP,Java. haviourofsystemresourcesrepresentthemainfunctionalitiesanetworkman- agementsystemshouldprovide. agementdataarestoredindatabasesmaintainedontheelementstobemanaged. ofthesystem.accordingtothisapproach,themanagementofanetworktends ferredforprovidinghigh-levelinformation,whichareusefulforthemanagement Managementapplicationsrunonacentralstation,wheredataneedtobetrans- Intheapproachescurrentlyadoptedbythemainstandardplatforms,man- Thegrowingcomplexityofcomputernetworksrequirestheuseofsophisticated managementtechniques.monitoring,properlydetectingandcontrollingthebe- torequireaconsiderableamountofbandwidth,particularlywhensometroubles code,inordertoextendsucharchitecturesbymovingaportionofthe"intelligence"tothenodeswheredataareresident.inthisscenario,management agentsareplacedineachnode:theymonitorthestateofthenode,andcan performsimplemanagementfunctionsonthelocalnode.ifagentsndirreg- Inthiswork,ourpurposeisexploitingnewtechnologiesbasedonmobile inthenetworkarise,andanimmediatemanager'sactionisrequired. ularoperationconditions,acommunicationmechanismistriggeredamongthe

2 dierentagents,whichactivatetheappropriaterecoverystrategies.forexample,suchstrategiesconsistofsystemrecongurations,ofnewroutingstrategies, transferlargeamountsofdatafromtheremotenodestoacentralstation.only etc.manyofthemanagementdecisionsmaybetakenlocally,thusavoidingto high-levelinformationwillbetransferredtothecentralstationwherethenetworkmanageroperates.besides,intheproposedinfrastructure,agentsarenot staticallyresidentintheremotedevices.theycanmovefromanodetoanother, canbereplacedifnecessary,canbeequippedwithfunctionalitiesthathadnot beenenvisagedatthetimeofinstallation.allofthemanagementproceduresdo notneedtobemaintainedineachagent;someoftheseprocedureswouldmigratefromacentralnodetotheonewheretheywillbeexecuted,butonlywhen theybecomereallynecessary.suchfunctionalitiesmakethesystemobtained veryexible.besides,themanagementapplicationitselfhasbeenorganizedas amobileagent;inthiswaythemanagerofthenetworknolongerneedsaxed thedevelopmentandthemanagementofmobileagents,whichwascompletely position. implementedbyusingmap3(mobileagentsplatform).itisaplatformfor developedbyusingjavaattheuniversityofcatania[8].thisplatformgivesthe userallthebasictoolsneededforthecreationofagentbasedapplications.it Aprototypeofthenetworkmanagementsystemdescribedbeforehasbeen enablesustocreate,run,suspend,resume,deactivate,reactivatelocalagents,to stoptheirexecution,tomakethemcommunicatewitheachotherandmigrate. enabledustodevelopaplatformabletooperateinheterogeneousenvironments. TheuseofJava(thankstoitsindependencefromhwandswarchitectures) themainstrengthsofanapproachbasedonmobilecode.insection4,aftera mentwhichhavebeencreatedforovercomingsuchproblems:wealsooutline mainlimits.insection3wediscussthemainmodelsofdistributedmanage- basicconceptsoftraditionalnetworkmanagementsystems,andweoutlinetheir Therestofthispaperisorganizedasfollows:inSection2wepresentthe shortdescriptionoftheplatformmap,theagents(expresslycreated)andtheir functionalitiesaredescribed.finally,insection5wepresentourconclusionsand 2Traditionalsystemsofnetworkmanagement thefuturehintsfortheresearch. Currentnetworkmanagementsystemsadoptacentralizedparadigmaccording towhichthemanagementapplicationperiodicallyaccessesthedatacollectedby asetofsoftwaremodulesplacedonthenetworkdevices,byusinganappropriate whilethecommonmanagementinformationprotocol(cmip)[11]proposedby protocol. theisohasbeenusedonlyintheareaofnetworksfortelecommunications. theietfhasbecomethestandardprotocolofmanagementforipnetworks, TheSimpleNetworkManagementProtocol(SNMP)[3,10,11]proposedby 3MAPisavailableathttp://sun195.iit.unict.it/MAP

3 operate.thebasiccomponentsofsuchsystemsofnetworkmanagementarethe followingones: {oneormoremanagementstations(networkmanagementstationornms) Botharchitectureshaveasimilarapproach,andonlydierforthewaythey {somenodes(potentiallymanyofthem).amodulecalledagent4runsoneach {amanagementprotocol,whichisusedfortransferringthemanagementinformationamongthesnmp-agentsandthemanagementstations. node;itmonitorsandcollectsthedataofthenode. workadministratorsnormallyoperate),formonitoringandcontrollingthenet- workelements.theyaredevicessuchashosts,routers,bridges,terminalservers, SomemanagementapplicationsareexecutedintheNMS(onwhichthenet- etc.,whichcanbemonitoredand/orcontrolledbyaccessingtheirmanagement information.themanagementinformationareconsideredasacollectionofmanagedobjects,storedinso-calledmanagementinformationbase(mib)[7].some setsofrelatedobjectsaredenedinthemibmodules.suchmodulesarespecied byusingasubsetofthestandardnotationosiabstractsyntaxnotationone ofthisinfrastructureareentitiesprovidingsuchinformationwithastandardizedinterface.thenmsinteractswiththesesnmp-agents,actingasaclient (ASN.1),calledStructureofManagementInformation(SMI).Thesnmp-agents that(accordingtotheindicationsofthenetworkmanager)askstheagentsfor informationaboutthedierentnetworkdevices. Snmp-agentshaveaverysimplestructure,andusuallycommunicateonlyin responsetotherequestsofvariablescontainedinthemib.theycannotperformmanagementactionsontheirlocaldata.thenetworkmanagementprotocolprovidestheprimitivesforexchangingmanagementinformationsamongthe AlltheapplicationsconcerningthemanagementareexecutedontheNMS. forcontinuingtoexaminethesubsequentvariableinthemib. isverysimple,andprovidesthreebasictypesofoperations:theoperatorsset snmp-agentsandthemanagementstations.theaccesstomibvariablesbythe NMStakesplaceatalowlevel.Forexample,thesetofprimitivesoftheSNMP 2.1LimitationsofthecentralizedparadigmoftheSNMP andgetforsettingorreadingthevalueofavariable,andtheoperatorgetnext workmanagementapplications,butthequickexpansionofnetworkshasposed ThecentralizedparadigmadoptedbytheSNMPisappropriateinseveralnet- theproblemofitsscalability,aswellasforanyothercentralizedmodel.atthe sametime,thecomputationalpowerofthenetworknodestobemanagedhas increased,andhasmadepossiblesignicantfunctionsofmanagementonthe nodesinadistributedmode. 4Theseagentsarenotrelatedwithmobileagentswhichwewilldiscusslaterinthis paper;toavoidconfusionwewillrefertothiskindofagentswiththetermsnmp-

4 needfordistributedcontrol,donotrequireafrequentpollingofmibvariables, andneedonlyalimitedamountofinformation.thetypicalexampleofthisis themonitoringandtherelateddisplayingofsomemibvariables.forexample, thestateoftheinterfaceofarouter,orthestateofalinkinvolveonlythequery Centralizationisgenerallyappropriatefortheapplicationswithalimited foracentralizedmanagement. andthedisplayingofalimitednumberofmibvariables,andisthereforesuitable thevariationsonahighnumberofmibvariables.inthesecases,themonitoring amountofinformation.anexamplecouldbethecomputationofafunctionthat severalmibvariables,whichneedtoperformsomecomputationsonalarge indicatesthefunctionalitylevelofthenetwork,whichmustfrequentlydetect Ontheotherendwehavesomeapplicationsrequiringafrequentpollingof inthetracquiteclosetothecongestedpartofnetwork. centralizedapproacharemoreevidentintheperiodsofnetworkcongestion, managementoperationsrequiredforovercomingthecongestioncauseanincrease whenthemanager'sactionisveryimportant.infact,duringthoseperiods,the andthecontrolshouldbeveryclosetothedevice.thesedrawbacksofthe 3Distributedmanagement Thedisadvantagesofatotallycentralizedarchitectureastheonedescribedbeforehavebeenadmittedbythesameorganizationsthathadintroducedit.A formofdecentralization(providedintherstversionofsnmp)isthemechanismofnoticationofasynchronousevents.infact,snmp-agentscansendtraps assimpleaspossible,theeventsthatanagentcancommunicatetothenms (thatis,messagestothenms)notasresultofarequest,butwhensomespecic usingtrapsareverysimple:typicalexamplesincludethechangeinthestateof eventsoccur.sincethebasicpurposeintheietfwasthatofmaintainingagents acomponent(forexample,fromactivetoinactive,andviceversa).inanycase, thetaskofsnmp-agentisonlythenoticationoftheevent:nomanagement actioncanbeperformedlocally,becauseanydecisionismadecentrallybythe NMS. aswidelyastherstversion,duetothefewimplementationsavailable,andto wheninteractingwithsuchdevices.however,thesnmpv2hasnotbeenused ofproxyagent,whichleadstoastructureofhierarchicalmanagement.aproxy agentisresponsibleforasetofdevices,andthenmssendstherequeststoit, TheSNMPv2[11]introducesanotherdecentralizationfeature:theconcept theexistenceofappropriatedevicescalledprobes,whosetaskistoprovideindicationsconcerningthenetworktracinaspecicsub-network,andconcerningthe theintroductionofthermon(remotemonitoring)[12].thermonassumes stateofsomedevices.thermonprovidesanapproachorientedtotheanalysis AnotherapproachtodecentralizationhasbeenproposedbytheIETFwith thecriticismmadeaboutthesecuritymodelintroduced. oftrac,ratherthantothedevice,asinthecaseoftheordinarysnmp-agents. Anyway,thebenetsoftheRMONconcernthesemanticcompressionofdata,

5 tothenms. 3.1Approachesbasedonmobilecode preprocessingallthecollectedinformation,andsendingonlythesignicantones toovercomesomelimitationsofcurrentcentralizedmanagementsystems.in Theuseofapproachesbasedonmobilecodefornetworkmanagementallows general,suchapproachesarebasedontheideaofreversingthelogicaccording micromanagementoperations,andreducingtheworkloadforthemanagement towhichthedataproducedbynetworkdevicesareperiodicallytransferredto stationandtheoverheadinthenetwork[2]. applicationscanbemovedtothenetworkdevices,thusperforming(locally)some thecentralmanagementstation.thankstosuchtechnologies,themanagement showsanarchitecturewherethemanagementstation,sendssomecommands delegatingtheremoteagenttotheactualexecution.ofcourse,remotedevices totheremotedevice(insteadoflimitingtotherequestformibvariables), code.infact,theideaofmanagementbydelegation,whichispresentin[6,5], Thisideawasexpressedbeforedevelopingtherstsystemsbasedonmobile includeaso-calledelasticprocessruntimesupport,whichcanprovidefornew servicesanddynamicallyextendtheonespresentinthedevice. thatcantakeadvantagefromtheadoptionofaspecicschemebasedonthe aremoreexible. delegationasaparticularcase,sincetheireldofapplicationiswider,andthey Inthefollowingparagraphswewillexaminethemanagementfunctionalities Theapproachesbasedonamobilecodemayincludethemanagementby considerablyimprovestheexibilityprovidedbyanetworkmanagementsystem. mobilityofthecode. UseofCodeonDemandTheuseofaparadigmbasedonCodeonDemand Infact,thestructureoftheMIBintheSNMPapproach(aswellasthetypeof followedwhiledevelopingthesnmp,duetothelimitedcomputationcapabilities managementagentsassimpleaspossiblewasoneoftheprojectrestrictions andcannotbemodied.thesnmp-agentcaninnowaymanageeventsdened bytheuser,noritcanactlocallywithoutinvolvingthenms.maintaining eventsthatcanbenotiedtothecentralstation)iscodiedinthesnmp-agent, inanagent.infact,afunction(duetothespecicnatureofsuchapplications) think(thisisnoteective)ofstaticallycodifyingallthemanagementfunctions morepowerfulprocessors,andhigheramountsofmemory.however,wecannot ofnetworkdevices.thiswastrueuntilsomeyearsago.now,suchdeviceshave mightberequestedonlyonsomedevices.onotherdevicesitcouldbeseldom devicesitcouldnotbenecessary.itisthereforeclearthatthestaticinclusionof requested;onotheronesitmightberequestedmorefrequently,whileinother suchfunctionsinanagentwouldleadtoaconsiderablewasteofresources. ofthesystem,andmaintainsagentssimpleandsmallatthesametime.only TheuseofanapproachbasedonCodeonDemandincreasestheexibility

6 serveranddynamicallyexecuted[9,8].inthesameway,eachsoftwareupdate whenafunctionbecomesnecessaryonanode,itcanbedownloadedfromacode withtheissueofthebandwidthwastethatoccursinacentralizedsystemwhen UseofRemoteEvaluationTheuseofRemoteEvaluationallowstodeal requestedbytheagentcanbeobtainedthroughthisapproach. thedataofthedevice,theyhavetobemovedfromtheagenttothenms,where micromanagementoperationsareneeded. wheretheywillbeexecutedwithoutgeneratingtracinthenetwork(except theyareprocessed.conversely,thankstothemechanismofremoteevaluation, theactionstobeperformedcanbedevelopedandsenttotheremotedevice, Inatraditionalsystem,nomatterwhichprocessinghastobeperformedon theinitialoneforsendingthecodetobeexecuted). ofthisfunctionisperformedbytransferringthevariablesinvolvedtothenms elementarymanagementvariables.eachvariableprovidesaparticularmeasure 4].Ingeneral,byhealthfunctionwemeananexpressionconsistingofseveral concerningthedevicetobecontrolled.intraditionalsystemsthecomputation Atypicalexampleisthecomputationoftheso-calledhealthfunctions[5,8, bandwidthoccupiedonthenetwork(andthecomputationalloadproducedon thenms)willbe.evenifthisfunctioncanbecodiedwithintheagent,this frequencyatwhichsuchfunctionhastobecomputed),thelargertheamountof onsite.inthisway,thehigherthenumberofthevariablesinvolved(orthe (throughpollingoperationsatregulartimeintervals),anddoingthecomputation isnotconvenientforthefollowingreasons:theincreaseinthesizeoftheagent beseldomused. andtheineciencyofthesystemduetothefactthatagenericfunctionmight formssuchcomputationswillbesentbythenmsanddynamicallyexecuted. Thisapproachallowstoobtainwhatiscalled"semanticcompressionofdata". functionsdirectlyonthedevices,andonlywhennecessary.thecodethatper- Infact,generallythemanagerofanetworkisnotinterestedinthesinglevalueof ByusingatechnologybasedonRemoteEvaluation,wecancomputethese amibvariable,butinaggregatevaluescontaininghigher-level"informations". Wecanthereforedevelopasysteminwhichthemanagerwritesitsmanagement functions(ortheymightbealreadyavailable),andtheninvokestheirremote morebenetstotheonesthatcanbeobtainedwithremoteevaluation.infact, UseofmobileagentsTheuseofapproachesbasedonmobileagentsadds executiononspecicdevices,whennecessary. inthiscasetheactiononadeviceisalwaysexpresslystartedbythenms. themovementsallowstodevelopapplicationsinwhichtheagentmovesfroma Conversely,inthecaseofmobileagents,theabilitytostorethestateduring devicetoanother,performingthemanagementfunctionsrequired.besides,the agentcanbedelegatedthetaskofdecidingwhereandwhentomigrateaccording toitscurrentstate,thusreducingtheinteractionwiththenms,andmaking processingsmoredistributed.

7 inwhichthenmshastomanagedierentlansandislinkedtothemby unreliableand/orlowbandwidthlinks.inthesecases,atraditionalapproach, whichrequirestheexchangeofseveralmessagesamongthenmsandremote devicesforasingleoperation,wouldmeandelaysintheexecutionofmanagement ThereducedinteractionwiththeNMSisanadvantageifwerefertosituations agivenoperation(whichhasbeendevelopedaccordingtothisnewmodelasa operations,aswellastheirunreliability.conversely,ifweusemobileagents,once mobilecomponent)issenttotheremotelan,itcanberunthere.evenifthe agent'ssizeincreases,therewillbenonegativeeect,sinceinalanwecan alwaysassumetohavelargebandwidthsavailable. implemented.mapisaplatformforthedevelopmentandthemanagementof InthissectionweintroducetheagentsystemMAP[8]thatwedevelopedand mobileagentsthatgivesalltheprimitivesneededfortheircreation,execution, 4NetworkmanagementusingMAP communication,migration,etc. onthedierenthardwareandsoftwarearchitectures.javaisalsousedasa languageforprogrammingagents:theprogrammerwillnotthereforeneedto bytheplatform. learnseveraland/orspeciclanguages,butonlytheapithataremadeavailable IthasbeenentirelydevelopedinJava,andthisguaranteesitstotalportability areabletocarrythedatastatewiththem,butnottheexecutionstate.besides, theexploitationofthejavamechanismsofclassesdynamicloading.agraphic interfacemanagestheagentsinexecution:thisinterfaceallowstoverifywhich itintegratestheparadigmsofremoteexecutionandcodeondemand,thanksto ThemigrationfacilityimplementedinMAPisaweakmigration:theagents Besides,throughthisinterfacewecantriggertheexecutionofanyagentpresent inthesystem,independentlyofwheretheagentcodeisresident. agentsareactiveinthelocalserver,andwhichonesarepresentinremoteservers. operationsofanetwork.thepurposeoftheimplementedagentsistoprovethe havedevelopedanagent-basedapplicationforperformingthebasicmanagement oftheissuesdescribedbefore.inparticular,usingthedevelopedagentsweare eectivenessofanapproachbasedonthemobilityofthecodeforsolvingsome Inthissectionweshowhow,byusingtheservicesoftheMAPplatform,we goingtodealwiththefollowingissues: {collectionofinformationaboutthestateofthenetwork andrun,hasbeenstructuredasanagent(calledsnmp-monitoring).throughthe {micromanagementofnetworkdevicesthroughthemonitoringofhealthfunctionsdenedbytheuser. graphicalinterfaceofthisagent(showninfigure1)wecanselecttheagentsto Theapplicationthroughwhichtheactualmanagementagentsaretriggered evaluatetheinformationcollectedbytheagentsthathavenishedtheirtask. besenttothenetwork,controlthelistoftheactiveagentsinthenetwork,and

8 , Throughthisbox,thetypicalparametersforakindofagentcanbespecied. Accordingtothetypeofagentselected,anappropriatedialogboxisviewed. Fig.1.Graphicalinterfaceoftheapplicationsnmp-monitoring Therearesomeadvantagesinstructuringthe"snmp-monitoring"applicationas MAPserverispresent,thusreleasingthemanagerfromtheconsoleoftheNMS. anagent:themanagementapplicationcanbeactivatedfromanynodewherea integrationandcompatibilitywiththesnmpworld.forthisreason,inour systemwehaveintegratedandusedsomeclassescreatedbyadvent[1],which implementthesnmpstack.inthisway,wehavehadtheopportunitytointeract withthedierentnodesofthenetworkthroughstandardmibvariables.atthe Oneofourpurposesinthecreationoftheplatformhasbeenthecomplete sametimethedevelopedframeworkallowsustomonitornon-standardquantities 4.1Agentsforthemanagement (notdenedbyamib)denedbytheuser. Wehavedevelopedthefollowingbasictypesofmobileagentsforthemanagement: {browseragent {daemonagent {messengeragent

9 performevenverycomplexactionsofmanagement.however,ourpurposeisnot creatingacompletemanagementsystem,butshowinghowtheideaspresented {verieragent beforecanbeeasilyimplementedbyouragentssystem. Theyperformverysimpletasks,butthecombinationoftheiractionsallowsto carriedout. BrowseragentThebrowseragentcollectssomeMIBvariablesfromasetof Belowwedescribethedetailsandthefunctionalitiesofeachtypeofagent nodesspeciedbytheuser.boththevariablesofthemib-treetobecollected reachestherstnodetobevisited,opensasnmplocalcommunicationsession, (Figure2)oftheapplication"snmp-monitoring".Afterbeingstarted,theagent andtheserverstobevisitedareselectedthroughanappropriatedialogbox buildsapdu-requestcontainingthemibvariablestobesearched,waitsfor thereplyfromthesnmpdaemon,andsavesthedataobtainedinaninternal structure.then,ifothernodesneedtobevisited,itreachesthem,andrepeats ithasbeenlaunched,wheretheresultsoftheresearchareshown. theprocedurementionedabove.otherwise,itreturnstotheplatformfromwhich, inanordinarymibbrowser,afteractivatingaconnectionwithaspecicnode, ThisagentrealizesthefunctionalitiesofanextendedMIBbrowser.Infact, Fig.2.Graphicalinterfaceofthebrowseragent wecanviewthecontentsofthemibvariables,bysendingasnmprequesttothe nodeinquestionforeachvariable.conversely,throughthebrowseragent,such

10 DaemonagentThedaemonagentmonitorsa"healthfunction"denedbythe requestsarerstgiventotheagent,which(bymovingfromanodetoanother) interactswiththemlocallyandreportstheglobalresulttotheinitialstation. agentmovestothenodeinquestion,whereitrecordsthevalueofthefunction: user.forstartingtheagent,thefunctiontobecomputedandthenodeofthe network(wherethecomputationhastobedone)mustbeprovided.thenthis ifthevalueishigherthanaxedthreshold(denedbytheuser),anotication messageissenttotheserverfromwhichtheagenthasdeparted. canimplement(bymeansofthisagent)amechanismofgeneralizedtrap,where haveanythingpreinstalled. theeventsinwhichthenmsisnotiedcanbefreelyandveryexiblysetby theuser.remotenodes(thankstotheuseofthemobilecode)donotneedto Figure3showsthebasicfunctioningmechanismsofthedaemonagent.We (1) Migration and execution on the remote node of AgentDaemon 1100 (2) Warning message:, threshold value exceeded (1) (1) AgentDaemon: (1) Fig.3.Computingcustomizedhealthfunctionsbymeansofdaemonagents (1) Y1 (2) AgentDaemon: Y2 (2) Snmp-monitoring (1) application MessengeragentThetwoagentsdescribedbeforedirectlyinteractwiththe Snmpdaemonpresentinthedierentnodes(throughtheAdventclasses).Conversely,themessengeragent,duringitsmigrationthroughthenodesofthe (1) theserverswheretheyhavetobesearched,and(ifnecessary)alsothenumberof network,interactswithotheragentsforcollectingspecicinformationproduced timestheagenthastocontactsuchagents.thus,themessengeragentperforms bythem. Infact,sincedaemonagentscanperformthecomputationofanyfunctiononthe operationsatahigherabstractionlevelthanthemereretrievalofmibvariables. Duringthecongurationweneedtoselecttheagentstobecontactedand thusobtainingageneraldescriptionaboutthestateofthenetwork. dierentnodesofthenetwork,themessengerallowstocollectsuchinformation,

11 ure4.itmustbenoticedthatthemodeloftheagentsinvolvedinthisarchi- tectureisalwaysthesame.thefunctionstobecomputedoneachnode,which clearlydependonthespecicenvironmentwhereweoperate,needtobechanged forobtainingsignicantinformationaboutthenetwork(belowwewillshowthe TheschematicbehaviourofamessengeragentisgraphicallyshowninFig- simplestepstobefollowedforinsertingnewmonitoringfunctionsinthesystem). Agent Messenger: on each node interacts with the local agents, executing on that node Fig.4.Messengeragent:interactionwithothersystemagents AgentDaemon: health function Y1 AgentDaemon: health function Y2 Snmp-monitoring application agementaction.itstaskisthatofbringingimportantinformationtothebase, VerieragentTheverieragentdoesnotperformanactualnetworkman- whichmightbeusefulforfurtheroperationsofnetworkmanagement.itvisits poseistheevaluationofthepresenceofaspecicpropertyofthesystemvisited thenodesselectedduringtheconguration,andcomputesafunctionwhosepur- (forexample,wemightthinkofthevericationofasoftwareversion,orthe availablespaceondisknotbelowaxedthreshold,orthevericationofsome logles,etc.).theverieragentthenreportstheserver,fromwhichitdeparted, thelistofthenodesthatcorrespondtothisproperty. 4.2Addingnewfunctionstothesystem cancomputeonthedierentnodes.thesystemproposedallowstodevelopand Intheagentsdescribedbeforewehavereferredtoseveralfunctionsthatthey addnewfunctionsveryeasily.infact,byrespectingsomeverysimplerules,any functioncanbeinsertedinthesystem.fromthepointofviewoftheimplementation,anabstractclassfunctionispresent,whichisasortoftemplatefor abstractpublicclassfunctionimplementsserializable{ buildingnewfunctions. Thisisthedenitionofthisclass:

12 abstractpublicvoidinitfun(stringmf); extenderthisclass,byimplementingthetwomethodsinitfun(whichiscalled }Auserwhowishestowritehis/herownmonitoringfunction,onlyneedsto abstractpublicvectorcalc(); onlyoncebeforestartingthefunction)andcalc(whichperformstheactualcomputation).besides,theusercanaccessthemibvariablesthroughappropriate classesineachnode. thedescriptionclasshastobeginbydfun. theclassmustbeginbyfunfollowedbyanystring.thenaclassofdescription class,whoseonlymethodcalledgetdesneedstobeimplemented.thenameof mustbecreatedforeachfunction.eveninthiscasewehavecreatedanabstract Then,inordertousethisfunctioninthemanagementsystem,thenameof wewillbeabletodistinguishfunctionsanddescriptionsfromalltheremaining inanynodewherethemapserverisactive.theagentswillbeabletouse classespresentinthesystem.wewillhavetheopportunitytostoresuchclasses themanyway,thankstothedynamicloadingoftheclassespresentintheagent Ifwefollowsuchsimplerulesinthecongurationdialogboxesoftheagents, platform. 5Conclusions Inthispaperwehavepresentedasystemofnetworkmanagementbasedon ofthedierentprogrammingparadigms,basedonamobilecode. theadoptionofthesetechnologies,comparingandevaluatingtheapplicability mobileagentstechnologies.wehavediscussedthemainbenetsderivingfrom browser.thepossibilityofcustomizingthenetworkfunctionstobemonitored formingbasicnetworkmanagementfunctionalities,includingageneralizedmib mentsinthisworkconcernthedenitionofmorecomplexhealthfunctions,and isoneofthemostinterestingaspectsoftheproposedapproach.futuredevelop- ByusingtheMAPagentsplatform,wehavedevelopedsomeagentsforper- ofagentsthatcouldadapttheirmigrationdynamicallyaccordingtothetypeof tasktheyhavebeenrequested. Acknowledgments ThisworkhasbeencarriedoutunderthenancialsupportoftheItalianMinisterodell'UniversitaedellaRicercaScienticaeTecnologica(MURST)inthe References mancesystemsfordistributedapplications)project. frameworkofthemosaico(designmethodologiesandtoolsofhighperfor- 1.AdventNet.AdventNetSNMPtools.

13 2.M.Baldi,S.Gai,andG.P.Picco.ExploitingCodeMobilityinDecentralizedand 3.J.D.Caseetal.ASimpleNetworkManagementProtocol(SNMP).RFC1157, FlexibleNetworkManagement.InProceedingsoftheFirstInt.WorkshoponMobileAgents(MA97),Berlin,Germany,April G.GoldszmidtandY.Yemini.DistributedManagementbyDelegation.Proc.of 4.G.Goldszmidt.OnDistributedSystemManagement.ProceedingsoftheIFIP the15thinternationalconferenceondistributedcomputingsystems,1995. InternationalSymposiumonIntegratedNetworkManagement, G.Goldszmidt,Y.Yemini,K.Meyer,M.Erlinger,J.Betser,andC.Sunshine.DecentralizingControlandIntelligenceinNetworkManagement.Proc.ofthe4th InternationalSymposiumonIntegratedNetworkManagement,May1995. mentoftcp/ip-basedinternets:mib-ii.rfc1213, K.McCloghrieandM.Rose.ManagementInformationBaseforNetworkManage- 8.A.Puliato,O.Tomarchio,andL.Vita.MAP:DesignandImplementationofa 10.MarshallT.Rose.NetworkManagementisSimple:youjustneedtheRightFrame- 9.A.Puliato,O.Tomarchio,andL.Vita.AJava-basedDistributedNetworkMan- MobileAgentPlatform.JournalofSystemArchitecture.tobepublished. agementarchitecture.in3rdint.conferenceoncomputerscienceandinformat- ics(csi'97),durham(usa),march W.Stallings.SNMP,SNMPv2,andCMIP.Thepracticalguidetonetworkmanagementstandards.AddisonWesley, S.Waldbusser.RemoteNetworkMonitoringManagementInformationBase.RFC work.proceedingsoftheifipsecondinternationalsymposiumonintegratednet- workmanagement, ,1995. ThisarticlewasprocessedusingtheLATEXmacropackagewithLLNCSstyle