第54題： 以下關于三層交換機的敘述中，正確的是(   )。
A.三層交換機包括二層交換和三層轉發(fā)，二層交換由硬件實現(xiàn)，三層轉發(fā)采用軟件實現(xiàn)
B.三層交換機僅實現(xiàn)三層轉發(fā)功能
C.通常路由器用在單位內部，三層交換機放置在出口
D.三層交換機除了存儲轉發(fā)外，還可以采用直通交換技術
答案解析與討論：m.xiexiliangjiufa.com/st/404761213.html

第55題： IP數(shù)據(jù)報首部中IHL (Internet首部長度)字段的最小值為(   )。
A.5
B.20
C.32
D.128
答案解析與討論：m.xiexiliangjiufa.com/st/4047728459.html

第56題： 查看OSPF接口的開銷、狀態(tài)、類型、優(yōu)先級等的命令是( 1 )；查看OSPF在接收報文時出錯記錄的命令是( 2 )。
（1）A.display ospf
B.display ospf error
C.display ospf interface
D.display ospf neighbor
（2）A.display ospf
B.display ospf error
C.display ospf interface
D.display ospf neighbor
答案解析與討論：m.xiexiliangjiufa.com/st/4047919870.html

第58題： 如下圖所示，使用基本ACL限制FTP訪間權限，從給出的Switch的配置文件判斷可以實現(xiàn)的策略是(   )。

①PC1在任何時間都可以訪問FTP
②PC2在2018年的周一不能訪問FTP
③PC2在2018年的周六下午3點可以訪問FTP
④PC3在任何時間不能訪問FTP

A.①②③④
B.①②④
C.②③
D.①③④
答案解析與討論：m.xiexiliangjiufa.com/st/4048529892.html

第59題： The TTL field was originally designed to hold a time stamp, which was decremented by each visited router. The datagram was ( 1 ) 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 ( 2 ) number of hops (routers) visited by the datagram. When a source host sends the datagram, it ( 3 ) 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 ( 4 ).This field limits the ( 5 ) of a datagram.
（1）A.received
B.discarded
C.rejected
D.tansferred
（2）A.maximum
B.minimum
C.exact
D.certain
（3）A.controls
B.transmits
C.stores
D.receives
（4）A.switch
B.router
C.source host
D.destination host
（5）A.lifetime
B.moving time
C.receiving time
D.transmitting time
答案解析與討論：m.xiexiliangjiufa.com/st/4048627556.html