以太网的最大帧长为1518字节，每个数据帧前面有8个字节的前导字段，帧间隔为9.6μs，快速以太网100 BASE-T发送两帧之间的最大间隔时间约为( ) μs。

A. 12.1
B. 13.2
C. 121
D. 132

下列命令中，不能用于诊断DNS故障的是( )

A. netstat
B. nslookup
C. ping
D. tracert

IP数据报首部中IHL (Internet首部长度)字段的最小值为( )

A. 5
B. 20
C. 32
D. 128

TCP使用3次握手协议建立连接，以防止( );当请求方发出SYN连接请求后，等待对方回答( )以建立正确的连接; 当出现错误连接时，响应( )。（20）A．出现半连接B.无法连接C.产生错误的连接D.连接失效（21）A．SYN,ACKB.FIN,ACKC.PSH,ACKD.RST,ACK（22）A．SYN,ACKB.FIN,ACKC.PSH,ACKD.RST,ACK● ARP 协议数据单元封装在( )中传送。（23）A．IP 分组B.以太帧C.TCP 段D.ICMP 报文

在BGP4协议中，路由器通过发送( )报文将正常工作信息告知邻居。当出现路由信息的新增或删除时，采用( )报文告知对方。（24）A．helloB.updateC.keepaliveD.notification（25）A．helloB.updateC.keepaliveD.notification

IEEEE 802.11i 标准制定的无线网络加密协议( )是-一个基于( )算法的加密方案。（42）A．RC4B.CCMPC.WEPD.WPA（43）A．RSAB.DESC.TKIPD.AES

MD5是( )算法，对任意长度的输入计算得到的结果长度为( )位。（44）A．路由选择B.摘要C.共享密钥D.公开密钥（45）A．56B.128C.140D.160

在SNMP 协议中，管理站要设置被管对象属性信息，需要采用( )命令进行操作;被管对象有差错报告，需要采用( )命令进行操作。（46）A．getB.getnextC.setD.trap（47）A．getB.getnextC.setD.trap

查看OSPF接口的开销、状态、类型、优先级等的命令是( )；查看OSPF在接收报文时出错记录的命令是( )（66）A． display ospfB. display ospf errorC. display ospf interfaccD. display ospf neighbor（67）A． display ospfB. display ospf errorC. display ospf interfaceD. display ospf neighbor

The TTL field was originally designed to hold a time stamp, which was decremented by each visited router. The datagram was ( ) when the value became zero. However, for this scheme, all the machines must have synchronized clocks and must know how long it takes for a datagram to go from one machine to another. Today, this field is used mostly to control the ( ) number of hops (routers) visited by the datagram. When a source host sends the datagram, it ( ) a number in this field. Each router that processes the datagram decrements this number by 1. If this value, after being decremented, is zero, the router discards the datagram.This field is needed because routing tables in the Internet can become corrupted.A datagram may travel between two or more routers for a long time without ever getting delivered to the ( ).This field limits the ( ) of a datagram.（71）A．receivedB.discardedC.rejectedD.tansferred（72）A．maximumB.minimumC.exactD.certain（73）A．controlsB.transmitsC.storesD.receives（74）A．switchB.routerC.source hostD.destination host（75）A．lifetimeB.moving timeC.receiving timeD.transmitting time