正确答案: D

应用层

题目：SMTP工作在OSI哪一层（）

解析：D

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举一反三的答案和解析：

[单选题]The corporate head office of Ezonexam has a teleconferencing system that uses VOIP (voice over IP) technology. This system uses UDP as the transport for the data transmissions. If these UDP datagrams arrive at their destination out of sequence, what will happen?

UDP will pass the information in the datagrams up to the next OSI layer in the order that they arrive.

解析：解析：Explanation:

[单选题]A Ezonexam technician is troubleshooting connectivity problems between two routers that are directly connected through the serial line. The technician notices that the serial line is up but cannot see any neighbors displayed in the output of the show cdp neighbors command.In which OSI layer is the problem most likely occurring?

Data link

解析：解析：Explanation:Asthequestionstatesthatseriallineisup,itmeanstheproblemisnotontheNetworklayer.Theadministratorcannotseeanyoutputbyissuingtheshowcdpneighborscommand.ItmeansthatCDPisdisabledandCDPisaprotocolthatrunsoverLayer2(thedatalinklayer)onallCiscorouters,bridges,accessservers,andswitches.

[单选题]IP地址为：192.168.50.70，掩码为：255.255.255.248，则该IP地址所在子网的子网有效IP为（）

192.168.50.65---192.168.50.70

[单选题]路由器的配置文件startup-config存放在()里

NVRAM

[单选题]路由器当前的模式为“端口模式”，要退回到“特权模式”，应该使用的快捷键为（）

ctrl+z

[多选题]The Ezonexam network administrator wants to ensure that only a single web server can connect to pot Fa0/1 on a catalyst switch. The server is plugged into the switch's Fast Eth. 0/1 port and the network administrator is about to bring the server online. What can the administrator do to ensure that only the MAC address of this server is allowed by switch port Fa0/1? (Choose two)

Configure the MAC address of the server as a static entry associated with port Fa0/1

Configure port security on Fa0/1 to reject traffic with a source MAC address other than that of the server

解析：解析：Explanation:

[单选题]On the topic of VLSM, which one of the following statements best describes the concept of the route aggregation?

Combining routes to multiple networks into one supernet.

解析：解析：Explanation:

[单选题]IP地址为：192.168.50.70，掩码为：255.255.255.248，则该IP和掩码结合，共划分了多少个子网（不包括全0子网和全1子网）（）

30