问答题
【说明】某单位通过路由器实现NAT转换，网络拓扑结构如图8.26所示。其中所有服务器和客户机都使用私网地址，FTP服务器可对外提供服务。
路由器NAT映射地址及对应域名如表8.5所示。
（8）B
问答题
【说明】
某公司的网络结构如图7.14所示，所有PC共享公网IP地址211.156.168.5接入Internet，另外有两台服务器提供Web服务和FTP服务，服务器的内网和公网地址如表7.7所示。
（7）e1→2（8）ftp（9）允许
问答题【说明】Linux是一个类似UNIX的操作系统，其功能强大，适合构建网络服务平台，提供DNS、WWW、FIT、NAT等服务。
（1）/dev/hdal
（2）/dev/hdb7
（3）network
单项选择题
For (1) service, we need a virtual-circuit subnet. Let us see how that works. The idea behind virtual circuits is to avoid having to choose a new (2) for every packet sent. Instead,when a connection is established, a route from the(3) machine to the destination machine is chosen as part of the connection setup and stored in tables inside the (4) . That route is used for all traffic flowing over the connection, exactly the same way that the telephone system works.When the connection is released, the virtual circuit is also terminated. With connection-oriented service, each packet carries an (5) telling which virtual circuit it belongs to.
和
相加时溢出（b7、a7为符号标志），则（）。
