LANChapter16Word文档下载推荐.docx

LANChapter16Word文档下载推荐.docx

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∙CatalystTroubleshootingTools— 

Describesvariousshowcommandsandotherfacilitiesthatprovidefurtherinsightintonetworkoperations.

∙Logging— 

DiscusseshowtouseandconfigureCatalystfeaturestologsignificanteventswithyourequipment.

Throughoutthisbook,youhaveseensuggestionsontroubleshootingspecificareasrelevanttothechaptertopic.Thischapterdiffersinthatitfocusesonhighlevel,structuredtroubleshootingtechniquesintheLANswitchedenvironmentanddescribesanumberofresourcesandtoolsavailabletofacilitatetroubleshooting.

TroubleshootingPhilosophies

Troubleshootingphilosophiesvarydependingupontraining,knowledge,ability,suspicions,systemhistory,personaldiscipline,andhowmuchheatyouaregettingfromusersandmanagement.Manyphilosophiesfallapartwhenpressuremountsfromusersscreamingthattheyneednetworkservicesnow,andwhenmanagersapplyevenmorepressurebecausetheydonotunderstandorappreciatethecomplexitiesofnetworktroubleshooting.Ifyouaresusceptibletothesepressures,thiscausesyoutobecomeunstructuredinyourapproachandtodependuponrandomthoughtsandclues.Ultimately,thisincreasesthetimetorestoreordeploynetworkservices.Characteristicsofagoodtroubleshootingphilosophy,though,includestructure,purpose,efficiency,andthedisciplinetofollowthestructure.

Twophilosophicalapproachesarepresentedheretoorganizeyourthoughts.Thefirstmethodtobediscusseddescribesanapproachrecognizingproblemsbasedupontheirprobabilityofoccurrence.Theyarethencategorizedintooneofthree"

buckets"

forthedifferingprobabilities.Thisisthebucketapproachtotroubleshooting.

ThesecondapproachtacklesnetworkproblemsbasedupontheOSImodel.Eachlayerrepresentsadifferentnetworkstructurethatyoumightneedtoexaminetorestoreyournetwork.ThisistheOSImodelapproachfortroubleshooting.

Theapproachesreallytackleproblemsinaverysimilarmanner,butrepresentdifferentmethodsofrememberingtheapproach.Thesecondmethoddoesdiffer,though,initsgranularity.Thebucketapproachgroupstroublesintothreebuckets.Eachbucketcontainsproblemswithsimilarcharacteristicsandrepresentsareasofprobableproblems.ThesecondapproachtacklesproblemsthroughtheOSImodel.Themodelhelpstothinkthroughsymptomsandwhathigh-levelsourcesmightcausetheproblems.

Inreality,yourtroubleshootingtechniqueprobablyusesalittleofboth.ThebucketmethodlumpstheOSImodel,tosomeextent,intothreeareas.

Regardlessofwhichapproachyouuse,youmusthaveonefoundationalpiecetotroubleshootyournetwork:

documentation.

KeepandMaintainNetworkDocumentation

Oneelementforanytroubleshootingphilosophytoworkisfrequentlyabsent:

documentation.Manyadministratorsneglecttodocumenttheirnetwork,oriftheydo,theydonotkeepthedocumentationuptodate.Documentationprovidestheframeworktoanswerfundamentalquestionssuchas,"

Whatchanged?

"

or"

WhatconnectstodeviceX?

WhatLayer2pathsexistfrompointAtopointB?

Reconstructingthenetworktopologydocumentationduringacrisisdoesnotlenditselftoanefficientorstructuredtroubleshootingapproach.Youarenotdoingyourself,yourcareer,oryourusersanygoodwhenyouhavetotaketimeduringthecrisiseventtodeterminethenetworktopology.

Documentyournetworkwithbothelectronicmediaandold-fashionedpaper.Electronically,usespreadsheets,graphicsprograms,networkmanagementtools,oranyothermeansatyourdisposaltokeepthedocumentationuptodate.Electronicdocumentationhastheadvantageofportability;

however,ithasthedisadvantageoflimitedaccessandvulnerabilitytooutages.Ifyoukeepthedocumentationonyourlaptopordesktop,butmakeitinaccessibletoothersonyourstaffbyeithertakingitwithyouorusingpasswords,theycannotusethedocumentationwhenyouarenotaround.Forsecurityreasons（ortosatisfycompanypolitics）,youmightdesirethis,butinmostcasesthisisnotagoodpractice.

Paperversionsoffernon-dependenceupontheelectronicdevice,butfrequentlytendtobeoutdatedthroughneglect.Whenyoumakeanelectronicchange,makesurethatthepapercopyreflectsthechangeaswell.

Anotherunderutilizeddocumentationtoolexistsinyournetworkequipment.Mostequipmenthasbuilt-indocumentationfeaturessuchasdescriptionstringsforinterfaces,modules,chassis,andsoforth.Usethesetopromptyourmemoryforconnectivity.Ittakesonlyafewsecondstoputadescriptionstringontheportconfiguration.OntheCatalyst5000/6000,usethesetportnamemod_num/port_num[port_name]commandtodocumentinterfaceswithusefulinformation.Forexample,youmightindicatewhoorwhatattachestotheport.Iftheportisatrunk,indicatewhatCatalystitconnectsto.Aswithpreviousdocumentationdiscussions,besuretokeepthedescriptionscurrent.YouwillseetheportnameifyouusetheshowportstatuscommandasshowninExample16-1.Here,Ports1/1and3/1haveassignednamesindicatingthedevicetheportattachesto.

Example16-1Outputfromshowportstatus

Console>

showportstatusPortNameStatusVlanLevelDuplexSpeedType------------------------------------------------------------------------1/1Cat-Bconnected523normalhalf100100BaseTX1/2notconnect1normalhalf100100BaseTX2/1connectedtrunknormalhalf400RouteSwitch3/1LS1010Switch12notconnecttrunknormalfull155OC3MMFATM

TroubleshootingPhilosophy1:

TheBucketApproach

Thebucketapproachtotroubleshootinginvestigateslikelyproblemareasbasedupontheprobabilityofoccurrence.Itstructuresthoughtsintermsoftargetareasforinvestigation.Specificproblemareasfrequentlycreatethemajorityofsituationsyouarelikelytoencounter.Youcancategorizetheseproblemsandplacethemintooneofthreebuckets:

cabling,configuration,andusage/implementation（other）.Thefollowingsectionsdescribethekindsofthingstolookforfromeachbucket.Itissuggestedthattheprobabilityofoccurrencedecreasesforeachbucket,asdepictedbythesizeofthebucketsinFigure16-1.Thefirstbucket,Cabling,islargestbecauseitrepresentsthehighestprobabilityofoccurrence.Youshouldcheckforproblemsfromthisbucketfirstinyournetwork.Thesecondbucket,Configuration,containsanothergroupofproblems,buttypicallyhasfewerinstancesinyournetwork.Therefore,youchecktheseproblemsafterexaminingthecables.Thelastandsmallestbucket,Other,containsalloftheotherproblemsthatdon'

tnecessarilyfallintoeitherofthefirsttwo.Problemsfromthisbucketoccurtheleastandshouldbeexaminedlastinyoursystem.

Figure16-1ThreeBucketsofProblems

EachbucketisitsownPandora'

sBox.Unfortunately,noonestandsoverthebucketwarningeveryonetonotspillthebucket.Ithappens.Yourjobintroubleshootingistodeterminewhichbucketspilleditscontentsintoyournetwork.

Bucket1:

Cabling

Thebucketofcableproblemscontainsissuessuchaswrongcables,brokencables,andincorrectlyconnectedcables.Toooften,administratorsoverlookcablesasatroublesource.Thisisespeciallytruewheneverthesystem"

wasworking."

Thiscausestroubleshooterstoassumethatbecauseitwasworking,itmuststillbeworking.Theytheninvestigateotherproblemareas,onlytoreturntocablesaftermuchfrustration.

Commoncablemistakesduringinstallationgenerallyincludeusingthewrongcabletype.One,forexample,istheuseofacrossovercableratherthanastraightthroughcable,orviceversa.Thefollowinglistsummarizesmanyofthetypicalproblems:

∙Crossoverratherthanstraightthrough,orviceversa

∙Single-moderatherthanmultimode

∙Connectingtransmittotransmit

∙Connectingtothewrongport

∙Partiallyfunctionalcables

∙Cableworksinsimplexmode,butnotfull-duplex

∙Cablestoolongortooshortforthemedia

RememberthatwhenattachinganMDI（mediadependentinterface）porttoanMDI-X（mediadependentcrossoverinterface）port,youmustuseastraightthroughcable.Allothercombinationsrequireacrossovercabletype.Fortunately,usingthewrongcabletypekeepsthelinkstatuslightextinguishedonequipment.Thisprovidesacluethatthecableneedstobeexamined.Anextinguishedlinkstatuslightcanresultfromthecorrectcabletype,butabrokenone.Beawarethatanilluminatedlinkstatuslightdoesnotguaranteethatthecableisgoodeither.Themostthatyoucanconcludefromastatuslightisthatyouhavethecorrectcabletypeandthatbothpiecesofequipmentdetecteachother.Thisdoesnot,however,meanthecableiscapableofpassingdata.

AformofpartialcablefailurecanconfusesomenetworkoperationslikeSpanningTree.Forexample,ifyourcableworkswellinonedirection,butnottheother,yourCatalystmightsuccessfullytransmitBPDUs,butnotreceivethem.Whenthishappens,theconvergedSpanningTreetopologymightbeincorrectand,therefore,dysfunctional.

Note

Ihaveaboxfilledwithcablesthatwerehealthyenoughtoilluminatethestatuslightonequipment,butnotgoodenoughtotransmitdata.Consequently,Iwastedmuchtimeinvestigatingotherareasonlytocirclebacktocables.Ishouldhavestuckwithmytroubleshootingplansandcheckedthecablesratherthanbypassingit.Makesurethatyouhaveacable