w networkguide to networks, fourth edition.ppt
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1、Network+Guide to Networks,Fourth EditionChapter 13Ensuring Integrity and AvailabilityNetwork+Guide to Networks,4e2What Are Integrity and Availability?Integrity:soundness of networks programs,data,services,devices,and connectionsAvailability:how consistently and reliably file or system can be accesse
2、d by authorized personnelNeed well-planned and well-configured networkData backups,redundant devices,protection from malicious intrudersPhenomena compromising integrity and availability:Security breaches,natural disasters,malicious intruders,power flaws,human errorNetwork+Guide to Networks,4e3Viruse
3、sProgram that replicates itself with intent to infect more computersThrough network connections or exchange of external storage devicesTypically copied to storage device without users knowledgeTrojan horse:program that disguises itself as something useful but actually harms systemNot considered a vi
4、rusNetwork+Guide to Networks,4e4Types of VirusesBoot sector viruses:located in boot sector of computers hard diskWhen computer boots up,virus runs in place of computers normal system filesRemoval first requires rebooting from uninfected,write-protected disk with system files on itMacro viruses:take
5、form of macro that may be executed as user works with a programQuick to emerge and spreadSymptoms vary widelyNetwork+Guide to Networks,4e5Types of Viruses(continued)File-infected viruses:attach to executable filesWhen infected executable file runs,virus copies itself to memoryCan have devastating co
6、nsequencesSymptoms may include damaged program files,inexplicable file size increases,changed icons for programs,strange messages,inability to run a programWorms:programs that run independently and travel between computers and across networksNot technically virusesCan transport and hide virusesNetwo
7、rk+Guide to Networks,4e6Types of Viruses(continued)Trojan horse:program that claims to do something useful but instead harms systemNetwork viruses:propagated via network protocols,commands,messaging programs,and data linksBots:program that runs automatically,without requiring a person to start or st
8、op itMany bots spread through Internet Relay Chat(IRC)Used to damage/destroy data or system files,issue objectionable content,further propagate virusNetwork+Guide to Networks,4e7Virus CharacteristicsEncryption:encrypted virus may thwart antivirus programs attempts to detect itStealth:stealth viruses
9、 disguise themselves as legitimate programs or replace part of legitimate programs code with destructive codePolymorphism:polymorphic viruses change characteristics every time transferred Time-dependence:time-dependent viruses programmed to activate on particular dateNetwork+Guide to Networks,4e8Vir
10、us Protection:Antivirus SoftwareAntivirus software should at least:Detect viruses through signature scanningDetect viruses through integrity checkingDetect viruses by monitoring unexpected file changes or virus-like behaviorsReceive regular updates and modifications from a centralized network consol
11、eConsistently report only valid virusesHeuristic scanning techniques attempt to identify viruses by discovering“virus-like”behavior(may give“false positives”)Network+Guide to Networks,4e9Antivirus PoliciesProvide rules for using antivirus software and policies for installing programs,sharing files,a
12、nd using floppy disksSuggestions for antivirus policy guidelines:Every computer in organization equipped with virus detection and cleaning software Users should not be allowed to alter or disable antivirus softwareUsers should know what to do in case virus detectedNetwork+Guide to Networks,4e10Fault
13、 ToleranceCapacity for system to continue performing despite unexpected hardware or software malfunctionFailure:deviation from specified level of system performance for given period of timeFault:involves malfunction of system componentCan result in a failureVarying degreesAt highest level,system rem
14、ains unaffected by even most drastic problemsNetwork+Guide to Networks,4e11Power:Power FlawsPower flaws that can damage equipment:Surge:momentary increase in voltage due to lightning strikes,solar flares,or electrical problemsNoise:fluctuation in voltage levels caused by other devices on network or
15、electromagnetic interferenceBrownout:momentary decrease in voltage;also known as a sagBlackout:complete power lossNetwork+Guide to Networks,4e12UPSs(Uninterruptible Power Supplies)Battery-operated power source directly attached to one or more devices and to power supply Prevents undesired features o
16、f outlets A/C power from harming device or interrupting servicesStandby UPS:provides continuous voltage to device Switch to battery when power loss detectedOnline UPS:uses power from wall outlet to continuously charge battery,while providing power to network device through batteryNetwork+Guide to Ne
17、tworks,4e13ServersMake servers more fault-tolerant by supplying them with redundant componentsNICs,processors,and hard disksIf one item fails,entire system wont failEnable load balancingNetwork+Guide to Networks,4e14Server MirroringMirroring:one device or component duplicates activities of anotherSe
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