User`s guide

VMware, Inc. 39
Chapter 5 Discovery
Asimilarscenariomightalsooccurwithothertypesofservers,dependingonhowtheyareinstalled.
However,oftenthisisnotanissue:forexample,inthedefaultinstallationoftheApachewebserverunderRed
HatLinux,allconfigurationinformationisstoredinalocationthatisreadableby
thegeneralpublic(under
the/etcbranchofthefilesystem).Insuchcases,nogroupmembershipsarerequiredforADMtobeableto
readthisdetailedconfiguration.
SNMP
TheSimpleNetworkManagementProtocol(SNMP)isapopularandstandardprotocolforremotely
monitoringandmanagingvarioustypesofnetworknodes.Managednetworknodesareoftenregularservers,
butothernetworkdevicessuchasnetworkswitchesandnetworkprinterscanalsobemanagedusingSNMP.
SNMPisbasedonthe
notionofagentsrunningonthemanagednetworknodes.Anagentisasoftware
component,installedonthemanagednodethatcananswerremotequeriesaboutthestateofthemanaged
node.TheremotecomponentthatmakessuchqueriesistermedtheSNMPmanager.AtypicalSNMP
deploymentincludesmany
SNMPagentsinstalledonthevariousmanagednodes,andasingleSNMP
managerthatcollectsinformationfromallofthem.
ThemaindifferencesamongthethreeversionsofSNMP(1,2,and3)arethesecuritymechanisms.Versions1
and2relyonafairlyprimitivemechanismofcommunitystrings,each
definingadifferentsetofSNMP
operationsthatisperformed.Version3introducesmoreadvancedauthenticationandprivacymechanisms,
basedonusernamesandpasswords.SNMPagentsarebuiltintomostmodernoperatingsystems,butmight
needtobeturnedonorconfiguredtobeabletoproviderelevantinformation.The
informationthatisobtained
fromtheSNMPagentisdefinedinmodulescalledManagementInformationBase(MIB).ThecoreMIB,which
isavailableinmostagents,iscalledMIB‐2,anditsuppliessystemandhardwareinformation.
Detail Discovery with SNMP
ADMcanactasanSNMPmanagerandcollectinformationfromanyhostthathasanSNMPagentrunningon
it.AllversionsoftheSNMPprotocolarefullysupported.Forversions1and2,communitystringsareused.
Forversion3,youcanselecttheauthenticationandprivacymodesin
compliancewiththisnewerstandard.
SNMP Agent Deployment Recommendations
Firewall Settings
Bydefault,SNMPqueriesareperformedonUDPport161oftheagent,althoughthiscanbe changedifdesired.
IfthereisafirewallbetweentheADMapplianceandthemonitorednetwork,thisportneedstobeopenfor
connectionsthatareinitiatedbytheADMappliance.
Linux and Net-SNMP
TheSNMP
agentthatisbuiltintoLinuxdistributionsisNet‐SNMP(http://net‐snmp.sourceforge.net).This
agentrunsasaservicecalled“snmpd”andislocatedintheservicesdirectory/etc/init.d/.
ThedefaultNet‐SNMPconfigurationallowstheuseofthepubliccommunitystringwithSNMPversion2,to
querytheSNMPagent
forparticularsystemconfigurationitems.However ,thisdefaultconfigurationonly
allowsaccesstoaportionofthestandardMIB‐2informationbase.Specifically,itdoesnotallowqueryingthe
listofnetworkinterfaces,whichisaveryimportantpieceofinformation.
ToallowNet‐SNMPtoalsoreportthismissinginformation,
itisrecommendedthatyoumodifytheNet‐SNMP
configurationfilein/etc/snmp/snmpd.conf.Addthefollowinglinetothesectionofthefilethathaslines
startingwith“view”:
view systemview included .1.3.6.1.2.1.2
Windows
Windows2000isusuallyinstalledwithitsownSNMPagent.Ifitisnot,itisquicklyinstalledbyselecting:
ControlPanel>Add/RemovePrograms>Add/RemoveWindowsComponents>Managementand
MonitoringTools>Details>SimpleNetworkManagementProtocol.
Bydefault,thisserversupportsthe“public”communitystring
forqueryingsysteminformation.