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图6-3给出了不同类型IPSec数据包的封装示意图。其中，______工作在传输模式；______支持报文加密服务。
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图给出了不同类型IPSec数据包的封装示意图其中____1__工作在隧道模式___2___只支
a.和c.
b.和d.
a.和b.
c.和d.
图8-5给出了不同类型IPSec数据包的封装示意图其中74工作在隧道模式75只支持报文源身份认
（a）和（c）
（b）和（d）
（a）和（b）
（c）和（d）
图7-5给出了不同类型IPSec数据包的封装示意图其中69工作在隧道模式70只支持报文源身份认
仅a.和b.
仅b.
a.和c.
b.和d.
图22-14给出了不同类型IPSec数据包的封装示意图其中______工作在隧道模式______只支
仅a.和b.
仅b.
a.和c.
b.和d.
阅读以下说明根据要求回答问题 [说明] 某公司总部和分支机构的网络配置如图所示在路由器
图17-27中abcd为不同类型IPSec数据包的示意图其中1和2工作在隧道模式3和4支持报文加密
图6-3给出了不同类型IPSec数据包的封装示意图其中______工作在传输模式______支持报文
a.和b.
a.和c.
c.和d.
b.和d.
图17-27中abcd为不同类型IPSec数据包的示意图其中1和2工作在隧道模式3和4支持报文
A
B
C
D
试题四共15分阅读以下说明回答问题1至问题4将解答填入答题纸对应的解答栏内【说明】某公司总部和
图17-27中abcd为不同类型IPSec数据包的示意图其中1和2工作在隧道模式3和4支持报文
A
B
C
D
图7-5给出了不同类型IPSec数据包的封装示意图其中69工作在隧道模式70只支持报文源身份认
a.和c.
b.和d.
a.和b.
c.和d.
图17-27中abcd为不同类型IPSec数据包的示意图其中1和2工作在隧道模式3和4支持报文
A
B
C
D
下图给出了不同类型IPSec数据包的封装示意图其中1工作在隧道模式2只支持报文源身份认证和数据
a.和c.
b.和d.
a.和b.
c.和d.
图22-14给出了不同类型IPSec数据包的封装示意图其中______工作在隧道模式______只支
a.和c.
b.和d.
a.和b.
c.和d.
下列属于隧道技术的是
IP数据包可以用PPP包封装然后在DDN线路上传输
IPX数据包可以用IP包封装然后在Internet上传输
PPP数据包可以用IP包封装然后在Internet上传输
IP数据包可以用以太帧封装然后在以太网上传输
图8-5给出了不同类型IPSec数据包的封装示意图其中74工作在隧道模式75只支持报文源身份认
仅（a）和（b）
仅（b）
（a）和（c）
（b）和（d）
图17-27中abcd为不同类型IPSec数据包的示意图其中1和2工作在隧道模式3和4支持报文
A
B
C
D
图给出了不同类型IPSec数据包的封装示意图其中____1__工作在隧道模式___2___只支
仅a.和b.
仅b.
a.和c.
b.和d.
下图是主机A发送的数据包通过路由器转发到主机B的过程示意图根据图中给出的信息数据包2的目的IP地址
222.4.59.2和OOd0.63c3.3c41
222.4.59.1和OOe0.4c3a.285f
222.4.57.2和OOd0.63c3.3c41
222.4.59.2和OOe0.4c3a.285f
下图给出了不同类型IPSec数据包的封装示意图其中1工作在隧道模式2只支持报文源身份认证和数据
仅a.和b.
仅b.
a.和c.
b.和d.
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某省6个城市A～F之间的网络通信线路每条通信线路旁标注了其长度千米数如图28-1所示如果要将部分千兆通信线路改造成万兆通信线路以提升各个城市网络之间的通信容量则至少要改造总计15千米的通信线路这种总千米数最少的改造方案共有16个 16
Pharmingisascammingpracticeinwhichmaliciouscodeisinstalledonapersonalcomputerorservermisdirectingusersto___29___Websiteswithouttheirknowledgeorconsent.Pharminghasbeencalled"phishingwithoutalure". Inphishingtheperpetratorsendsoutlegitimate-___30___e-mailsappearingtocomefromsomeoftheWeb’smostpopularsitesinanefforttoobtainpersonalandfinancialinformationfromindividualrecipients.Butinpharminglargernumbersofcomputeruserscanbe___31___becauseitisnotnecessarytotargetindividualsonebyoneandnoconsciousactionisrequiredonthepartofthevictim.Inoneformofpharmingattackcodesentinane-mailmodifieslocalhostfilesonapersonalcomputer.ThehostfilesconvertURLsintothenumberstringsthatthecomputerusestoaccessWebsites.AcomputerwithacompromisedhostfilewillgotothefakeWebsiteevenifausertypesinthecorrectInternetaddressorclicksonanaffected___32___entry.Somespywareremovalprogramscancorrectthecorruptionbutitfrequentlyrecursunlesstheuserchangesbrowsing___33___ 32
Whenthesystemuponwhichatransportentityisrunningfailsandsubsequentlyreatartsthe___34___informationofallactiveconnectionsislost.Theaffectedconnectionsbecomehalf-openasthesidethatdidnotfaildoesnotyetrealizethepromble. Thestillactivesideofahalf-openconnectionsusinga___35___timer.Thistimermeasuresthetimetransportmachinewillcontinuetoawaitan___36___ofatransmittedsegmentafterthesegmenthasbeenretransmittedthemaximumnumberoftimes.Whenthetimer___37___thetransportentityassumesthateithertheothertransportentityortheinterveningnetworkhasfailed.AsaresultthetimerclosestheconnectionandsignalsanabnormalclosetotheTSuser. Intheeventthatatransportentityfailsandquicklyrestarthalf-openconnectionscanbeteminatedmorequicklybytheuseoftheRSTsegment.ThefailedsidereturnsanRSTitoeverysegmentithatitreceives.WhentheRSTireachestheothersideitmustbecheckedforvaliditydasedonthe___38___numberiastheRSTcouldbeinresponsetoanoldsegment.Iftheresetisvalidthetransportentityperformsanabnormaltermination. 38
某省广域骨干网的部分网络拓扑结构如图28-8所示图中标识出了各节点之间网络流量的传输能力单位Mbps从节点①到节点⑥的最大网络流量可以达到Mbps
Tocompeteintoday’sfast-pacedcompetitiveenvironmentorganizationsareincreasinglyallowingcontractorspartnersvisitorsandgueststoaccesstheirinternalenterprisenetworks.Theseusersmayconnecttothenetworkthroughwiredportsinconferenceroomsorofficesorviawirelessaccesspoints.InallowingthisopenaccessforthirdpartiesLANsbecome___19___.Thirdpartiescanintroduceriskinavarietyofwaysfromconnectingwithaninfectedlaptoptounauthorizedaccessofnetworkresourcesto___20___activity.Formanyorganizationshowevertheoperationalcomplexityandcoststoensuresafethirdpartynetworkaccesshavebeenprohibitive.Fifty-twopercentofsurveyedCISOsstatethattheycurrentlyuseamoatandcastle’ssecurityapproachandadmitthatdefensesinsidetheperimeterareweak.Threatsfrominternalusersarealsoincreasinglyacauseforsecurityconcerns.Employeeswithmaliciousintentcanlaunch___21___ofserviceattacksorsteal___22___informationbysnoopingthenetwork.Astheyaccessthecorporatenetworkmobileandremoteusersinadvertentlycaninfectthenetworkwith___23___andwormsacquiredfromunprotectedpublicnetworks.Hackersmasqueradingasinternaluserscantakeadvantageofweakinternalsecuritytogainaccesstoconfidentialinformation. 22
Whenthesystemuponwhichatransportentityisrunningfailsandsubsequentlyreatartsthe___34___informationofallactiveconnectionsislost.Theaffectedconnectionsbecomehalf-openasthesidethatdidnotfaildoesnotyetrealizethepromble. Thestillactivesideofahalf-openconnectionsusinga___35___timer.Thistimermeasuresthetimetransportmachinewillcontinuetoawaitan___36___ofatransmittedsegmentafterthesegmenthasbeenretransmittedthemaximumnumberoftimes.Whenthetimer___37___thetransportentityassumesthateithertheothertransportentityortheinterveningnetworkhasfailed.AsaresultthetimerclosestheconnectionandsignalsanabnormalclosetotheTSuser. Intheeventthatatransportentityfailsandquicklyrestarthalf-openconnectionscanbeteminatedmorequicklybytheuseoftheRSTsegment.ThefailedsidereturnsanRSTitoeverysegmentithatitreceives.WhentheRSTireachestheothersideitmustbecheckedforvaliditydasedonthe___38___numberiastheRSTcouldbeinresponsetoanoldsegment.Iftheresetisvalidthetransportentityperformsanabnormaltermination. 36
[说明]S省某高校的校园网络拓扑结构如图6-8所示根据该校信息化建设领导小组的要求要实现负载均衡和冗余备份构建无阻塞高性能的网络基础设施平台该校园网络采用两台S7010万兆骨干路由交换机作为双核心汇聚交换机或部门交换机通过光纤链路分别与两台核心交换机相连通过防火墙和边界路由器与Internet相连全网交换机都启用了MSTP生成树模式并配置了相同的实例域名称和版本修订号该校园网两台S7010之间相连的端口均为Trunk端口S7010与其下连的汇聚交换机或部门交换机之间相连的端口也均为Trunk端口假设校园网中每台核心交换机对数据帧的转发延时为10ms每台汇聚交换机或部门交换机对数据帧的转发延时为25ms每个数据帧经过所有通信线路的信号传输延时都为1ms暂不考虑传输距离等因素该校园网中部分PC的IP地址及所属VLAN等信息如表6-2所示表6-2部分PC的IP地址及所属VLAN网络设置IP地址所属VLAN网络设置IP地址所属VLANPC110.3.9.10/24VLAN5PC510.3.10.21/24VLAN6PC210.3.10.10/24VLAN6PC610.3.11.21/24VLAN7PC310.3.11.10/24VLAN7PC710.3.9.21/24VLAN5PC410.3.12.10/24VLAN8[问题2]在核心层交换机S7010-1中VLAN6的IP地址配置为10.3.10.1/24VLAN7的IP地址配置为10.3.11.254/24核心三层交换机S7010-1的部分VRRP配置信息如下S7010-1config#interfaceVLAN6S7010-1config-if#vrrp10ip10.3.10.1S7010-1config-if#vrrp10preemptS7010-1config#interfaceVLAN7S7010-1config-if#vrrp11ip10.3.11.1在核心三层交换机S7010-2中VLAN6的IP地址配置为10.3.10.254/24VLAN7的IP地址配置为10.3.11.1/24核心三层交换机S7010-1的部分VRRP配置信息如下S7010-2config#interfaceVLAN6S7010-2config-if#vrrp10ip10.3.10.1S7010-2config#interfaceVLAN7S7010-2config-if#vrrp11ip10.3.11.1S7010-2config-if#vrrp111PC5主机中设置的网关IP地址为10.3.10.1在网络正常运行的情况下请按照以下格式写出PC5访问Internet的数据转发路径格式PC5→设备1→→Internet不写返回路径2连接在交换机C2960S的PC3主机中设置的网关IP地址为10.3.11.1在网络正常运行的情况下请按照以下格式写出PC3访问Internet的数据转发路径格式PC3→设备1→→Internet不写返回路径3假设三层交换机S7010-1需要临时宕机25分钟进行板卡检修并升级操作系统请问这25分钟时段内PC5在没有修改原有网关IP地址的情况下能否访问Internet请结合交换机S7010-1宕机后发生的变化简要说明原因
TheBorderGatewayProtocolBGPisaninterautonomoussystem.___49___protocol.TheprimaryfunctionofaBGPspeakingsystemistoexchangenetwork___50___informationwithotherBGPsystem.ThisnetworkreachabilityinformationincludesinformationonthelistofAutonomousSystemASsthatteachabilityinformationtraverses.BGP-4providesanewsetofmechanismsforsupporting___51___interdomainrouting.ThesemechanismsincludesupportforadvertisinganIP___52___andeliminatetheconceptofnetworkclasswithinBGP.BGP-4alsointroducesmechanismsthatallowaggregationofroutesincluding___53___ofASpaths.Thesechangesprovidesupportfortheproposedsupernetttingscheme. 50
WLANsareincreasinglypopularbecausetheyenablecost-effectiveconnectionsamongpeopleapplicationsanddatathatwerenotpossibleornotcost-effectiveinthepast.ForexampleWLAN-basedapplicationscanenablefine-grainedmanagementofsupplyanddistribution___24___toimprovetheirefficiencyandreduce___25___.WLANscanalsoenableentirelynewbusinessprocesses.TocitebutoneexamplehospitalsareusingWLAN-enabledpoint-of-careapplicationstoreduceerrorsandimproveoverall___26___care.WLANmanagementsolutionsprovideavarietyofotherbenefitsthatcanbesubstantialbutdifficulttomeasure.Forexampletheycanprotectcorporatedatabypreventing___27___throughrogueaccesspoints.TheyhelpcontrolsalarycostsbyallowingITstaffstomanagelargernetworkswithoutaddingstaff.Andtheycanimproveoverallnetworkmanagementbyintegratingwithcustomers’existingsystemssuchasOpenView.Fortunatelyitisn’tnecessarytomeasurethesebenefitstojustifyinvestinginWLANmanagementsolutionswhichcanquicklypayforthemselvessimplybyminimizingtime-consuming___28___andadministrativechores. 26
若某个信道误码率为10-5数据帧帧长为10×103比特差错为单个错则帧出错的概率为
___39___isusedtoensuretheconfidentialityintegrityandauthenticityofthetwoendpointsintheprivatenetwork.___40___anapplication-layerprotocolauthenticateseachpeerinanIPSectransaction.IKEnegotiatessecuritypolicydeterminingwhichalgorithmmaybeusedtosetupthetunnel.Italsohandlestheexchangeofsessionkeysusedforthatonetransaction. Networksthatuse___41___tosecuredatatrafficcanautomaticallyauthenticatedevicesbyusingbyusing___42___whichverifytheidentitiesofthetwouserswhoaresendinginformationbackandforth.IPSeccanbeidealwaytosecuredatainlargenetworksthatrequiresecureconnectionsamongmanydevices. UsersdeployingIPSeccan___43___theirnetworkinfrastructurewithoutaffectingtheapplicationsonindividualcomputer.Theprotocolsuiteisavailableasasoftware-onlyupgradetothenetworkinfrastructure.Thisalowssecuritytobeimplementedwithoutcostlychangestoeachcomputer.MostimportantIPSecallowsinteroperabilityamongdifferentnetworkdevicesPCsandothercomputingsystems. 40
TheBorderGatewayProtocolBGPisaninterautonomoussystem.___49___protocol.TheprimaryfunctionofaBGPspeakingsystemistoexchangenetwork___50___informationwithotherBGPsystem.ThisnetworkreachabilityinformationincludesinformationonthelistofAutonomousSystemASsthatteachabilityinformationtraverses.BGP-4providesanewsetofmechanismsforsupporting___51___interdomainrouting.ThesemechanismsincludesupportforadvertisinganIP___52___andeliminatetheconceptofnetworkclasswithinBGP.BGP-4alsointroducesmechanismsthatallowaggregationofroutesincluding___53___ofASpaths.Thesechangesprovidesupportfortheproposedsupernetttingscheme. 52
某公司的销售收入状态如表3-5所示就销售收入而言该公司的盈亏平衡点是百万元人民币
WLANsareincreasinglypopularbecausetheyenablecost-effectiveconnectionsamongpeopleapplicationsanddatathatwerenotpossibleornotcost-effectiveinthepast.ForexampleWLAN-basedapplicationscanenablefine-grainedmanagementofsupplyanddistribution___24___toimprovetheirefficiencyandreduce___25___.WLANscanalsoenableentirelynewbusinessprocesses.TocitebutoneexamplehospitalsareusingWLAN-enabledpoint-of-careapplicationstoreduceerrorsandimproveoverall___26___care.WLANmanagementsolutionsprovideavarietyofotherbenefitsthatcanbesubstantialbutdifficulttomeasure.Forexampletheycanprotectcorporatedatabypreventing___27___throughrogueaccesspoints.TheyhelpcontrolsalarycostsbyallowingITstaffstomanagelargernetworkswithoutaddingstaff.Andtheycanimproveoverallnetworkmanagementbyintegratingwithcustomers’existingsystemssuchasOpenView.Fortunatelyitisn’tnecessarytomeasurethesebenefitstojustifyinvestinginWLANmanagementsolutionswhichcanquicklypayforthemselvessimplybyminimizingtime-consuming___28___andadministrativechores. 24
Themetricassignedtoeachnetworkdependsonthetypeofprotocol.SomesimpleprotocollikeRIPtreatseachnetworkasequals.The___44___ofpassingthrougheachnetworkisthesame;itisone___45___count.Soifapacketpassesthrough10networktoreachthedestinationthetotalcostis10hopcounts.OtherprotocolssuchasOSPFallowtheadministratortoassignacostforpassingthroughanetworkbasedonthetypeofservicerequired.A___46___throughanetworkcanhavedifferentcostsmetrics.Forexampleifmaximum___47___isthedesiredtypeofserviceasatellitelinkhasalowermetricthanafiber-opticline.Ontheotherhandifminimum___48___isthedesiredtypeofserviceafiber-opticlinehasalowermetricthanasatelliteline.OSPFalloweachroutertohaveseveralroutingtablebasedontherequiredtypeofservice. 46
[论专用网络的安全规划与设计]随着信息技术在世界范围内的迅猛发展特别是网络技术的普及应用电子政务网络电子商务网络工业网络应急指挥网络视频监控网络无线数字城市网络等专用网络正在成为当代信息化的重点标志性的建设项目为了保障网络的安全性和信息的安全性各种网络安全关键技术及安全产品得到了广泛使用请围绕专用网络的安全规划与设计论题依次对以下3个方面进行论述1．简述你参与规划设计的专用网络建设项目以及你所担任的主要工作2．具体讨论你在专用网络的安全规划与设计中针对特有的应用环境和需求采用了哪些关键技术和解决方案采取这些关键技术和解决方案有何优点3．分析和评估你所采用的专用网络安全措施的效果及其特色以及相关的改进措施
Themetricassignedtoeachnetworkdependsonthetypeofprotocol.SomesimpleprotocollikeRIPtreatseachnetworkasequals.The___44___ofpassingthrougheachnetworkisthesame;itisone___45___count.Soifapacketpassesthrough10networktoreachthedestinationthetotalcostis10hopcounts.OtherprotocolssuchasOSPFallowtheadministratortoassignacostforpassingthroughanetworkbasedonthetypeofservicerequired.A___46___throughanetworkcanhavedifferentcostsmetrics.Forexampleifmaximum___47___isthedesiredtypeofserviceasatellitelinkhasalowermetricthanafiber-opticline.Ontheotherhandifminimum___48___isthedesiredtypeofserviceafiber-opticlinehasalowermetricthanasatelliteline.OSPFalloweachroutertohaveseveralroutingtablebasedontherequiredtypeofservice. 44
某软件企业2011年初计划投资1000万人民币开发一套统一安全网关UTM产品预计从2012年开始年实现产品销售收入1500万元年市场销售成本1000万元该产品的分析员张工根据财务总监提供的贴现率制作了如表28-6所示的产品销售现金流量表根据表中的数据该产品的动态投资回收期是___17___年投资收益率是___18___ 表28-6某企业UTM产品销售现金流量表 年度 2011 2012 2013 2014 2015 投资 1000 —— —— —— —— 成本 —— 1000 1000 1000 1000 收入 —— 1500 1500 1500 1500 净现金流量 -1000 500 500 500 500 净现值 -925.93 428.67 396.92 367.51 340.29 18
Pharmingisascammingpracticeinwhichmaliciouscodeisinstalledonapersonalcomputerorservermisdirectingusersto___29___Websiteswithouttheirknowledgeorconsent.Pharminghasbeencalled"phishingwithoutalure". Inphishingtheperpetratorsendsoutlegitimate-___30___e-mailsappearingtocomefromsomeoftheWeb’smostpopularsitesinanefforttoobtainpersonalandfinancialinformationfromindividualrecipients.Butinpharminglargernumbersofcomputeruserscanbe___31___becauseitisnotnecessarytotargetindividualsonebyoneandnoconsciousactionisrequiredonthepartofthevictim.Inoneformofpharmingattackcodesentinane-mailmodifieslocalhostfilesonapersonalcomputer.ThehostfilesconvertURLsintothenumberstringsthatthecomputerusestoaccessWebsites.AcomputerwithacompromisedhostfilewillgotothefakeWebsiteevenifausertypesinthecorrectInternetaddressorclicksonanaffected___32___entry.Somespywareremovalprogramscancorrectthecorruptionbutitfrequentlyrecursunlesstheuserchangesbrowsing___33___ 30
某个高层报文被分为5帧进行传送帧出错的概率为0.1纠错重发以报文为单位则整个报文的平均发送次数约为次
假设某项网络工程项目由设备x1x2x3x4x5和设备y1y2串联组成其中设备x1必须在左端或右端且设备y1y2必须相邻则共有种排法
___39___isusedtoensuretheconfidentialityintegrityandauthenticityofthetwoendpointsintheprivatenetwork.___40___anapplication-layerprotocolauthenticateseachpeerinanIPSectransaction.IKEnegotiatessecuritypolicydeterminingwhichalgorithmmaybeusedtosetupthetunnel.Italsohandlestheexchangeofsessionkeysusedforthatonetransaction. Networksthatuse___41___tosecuredatatrafficcanautomaticallyauthenticatedevicesbyusingbyusing___42___whichverifytheidentitiesofthetwouserswhoaresendinginformationbackandforth.IPSeccanbeidealwaytosecuredatainlargenetworksthatrequiresecureconnectionsamongmanydevices. UsersdeployingIPSeccan___43___theirnetworkinfrastructurewithoutaffectingtheapplicationsonindividualcomputer.Theprotocolsuiteisavailableasasoftware-onlyupgradetothenetworkinfrastructure.Thisalowssecuritytobeimplementedwithoutcostlychangestoeachcomputer.MostimportantIPSecallowsinteroperabilityamongdifferentnetworkdevicesPCsandothercomputingsystems. 42
利用M/M/1排队论模型分析图28-6所示的是一个简单的工作流模型其中单位时间为1小时它表示这样一个执行过程每小时将会有20个任务达到c1这20个任务首先经过处理task1再经过处理task2最终将结果传递到c3处理task1和处理task2相互独立且每个任务到达间隔服从负指数分布处理task1task2的平均等待时间分别是
在大多数网络中数据链路层主要是通过请求重发已损坏的数据帧的办法来解决发送出错问题如果一个帧被损坏的概率是P而且确认信息不会丢失则发送一帧的平均发送次数是
WLANsareincreasinglypopularbecausetheyenablecost-effectiveconnectionsamongpeopleapplicationsanddatathatwerenotpossibleornotcost-effectiveinthepast.ForexampleWLAN-basedapplicationscanenablefine-grainedmanagementofsupplyanddistribution___24___toimprovetheirefficiencyandreduce___25___.WLANscanalsoenableentirelynewbusinessprocesses.TocitebutoneexamplehospitalsareusingWLAN-enabledpoint-of-careapplicationstoreduceerrorsandimproveoverall___26___care.WLANmanagementsolutionsprovideavarietyofotherbenefitsthatcanbesubstantialbutdifficulttomeasure.Forexampletheycanprotectcorporatedatabypreventing___27___throughrogueaccesspoints.TheyhelpcontrolsalarycostsbyallowingITstaffstomanagelargernetworkswithoutaddingstaff.Andtheycanimproveoverallnetworkmanagementbyintegratingwithcustomers’existingsystemssuchasOpenView.Fortunatelyitisn’tnecessarytomeasurethesebenefitstojustifyinvestinginWLANmanagementsolutionswhichcanquicklypayforthemselvessimplybyminimizingtime-consuming___28___andadministrativechores. 28
[说明]某省级重点中学欲构建一个局域网考虑到该中学的很多现代化教学业务依托于网络要求中学内部用户能够高速访问相关的5台内部高性能服务器并且要求通过网络的冗余性设计来获得较高的各类业务服务的可用性某系统集成公司根据该中学的相关需求将网络拓扑结构设计为双核心来进行负载均衡和容错该公司给出的网络拓扑图如图6-7所示[问题3]在校外住宿的教职工要求使用校园网部分内部服务器以满足其备课及浏览校园信息等需求系统集成公司采用了IPSecVPN的远程接入方案请从安全保证角度简要叙述实现VPN的几种关键技术
[说明]某省级重点中学欲构建一个局域网考虑到该中学的很多现代化教学业务依托于网络要求中学内部用户能够高速访问相关的5台内部高性能服务器并且要求通过网络的冗余性设计来获得较高的各类业务服务的可用性某系统集成公司根据该中学的相关需求将网络拓扑结构设计为双核心来进行负载均衡和容错该公司给出的网络拓扑图如图6-7所示[问题1]根据用户需求和设计要求请指出图6-7中不合理的设计之处并给出相应的改进方案
Whenthesystemuponwhichatransportentityisrunningfailsandsubsequentlyreatartsthe___34___informationofallactiveconnectionsislost.Theaffectedconnectionsbecomehalf-openasthesidethatdidnotfaildoesnotyetrealizethepromble. Thestillactivesideofahalf-openconnectionsusinga___35___timer.Thistimermeasuresthetimetransportmachinewillcontinuetoawaitan___36___ofatransmittedsegmentafterthesegmenthasbeenretransmittedthemaximumnumberoftimes.Whenthetimer___37___thetransportentityassumesthateithertheothertransportentityortheinterveningnetworkhasfailed.AsaresultthetimerclosestheconnectionandsignalsanabnormalclosetotheTSuser. Intheeventthatatransportentityfailsandquicklyrestarthalf-openconnectionscanbeteminatedmorequicklybytheuseoftheRSTsegment.ThefailedsidereturnsanRSTitoeverysegmentithatitreceives.WhentheRSTireachestheothersideitmustbecheckedforvaliditydasedonthe___38___numberiastheRSTcouldbeinresponsetoanoldsegment.Iftheresetisvalidthetransportentityperformsanabnormaltermination. 34
Themetricassignedtoeachnetworkdependsonthetypeofprotocol.SomesimpleprotocollikeRIPtreatseachnetworkasequals.The___44___ofpassingthrougheachnetworkisthesame;itisone___45___count.Soifapacketpassesthrough10networktoreachthedestinationthetotalcostis10hopcounts.OtherprotocolssuchasOSPFallowtheadministratortoassignacostforpassingthroughanetworkbasedonthetypeofservicerequired.A___46___throughanetworkcanhavedifferentcostsmetrics.Forexampleifmaximum___47___isthedesiredtypeofserviceasatellitelinkhasalowermetricthanafiber-opticline.Ontheotherhandifminimum___48___isthedesiredtypeofserviceafiber-opticlinehasalowermetricthanasatelliteline.OSPFalloweachroutertohaveseveralroutingtablebasedontherequiredtypeofservice. 48
Tocompeteintoday’sfast-pacedcompetitiveenvironmentorganizationsareincreasinglyallowingcontractorspartnersvisitorsandgueststoaccesstheirinternalenterprisenetworks.Theseusersmayconnecttothenetworkthroughwiredportsinconferenceroomsorofficesorviawirelessaccesspoints.InallowingthisopenaccessforthirdpartiesLANsbecome___19___.Thirdpartiescanintroduceriskinavarietyofwaysfromconnectingwithaninfectedlaptoptounauthorizedaccessofnetworkresourcesto___20___activity.Formanyorganizationshowevertheoperationalcomplexityandcoststoensuresafethirdpartynetworkaccesshavebeenprohibitive.Fifty-twopercentofsurveyedCISOsstatethattheycurrentlyuseamoatandcastle’ssecurityapproachandadmitthatdefensesinsidetheperimeterareweak.Threatsfrominternalusersarealsoincreasinglyacauseforsecurityconcerns.Employeeswithmaliciousintentcanlaunch___21___ofserviceattacksorsteal___22___informationbysnoopingthenetwork.Astheyaccessthecorporatenetworkmobileandremoteusersinadvertentlycaninfectthenetworkwith___23___andwormsacquiredfromunprotectedpublicnetworks.Hackersmasqueradingasinternaluserscantakeadvantageofweakinternalsecuritytogainaccesstoconfidentialinformation. 20
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