2. 计算机
  3. An inbound access list has been configured on a serial interface to deny packet entry for TCP and UDP ports 21, 23 and 25． What

An inbound access list has been configured on a serial interface to deny packet entry for TCP and UDP ports 21, 23 and 25． What

admin2019-04-08  11
问题 An inbound access list has been configured on a serial interface to deny packet entry for TCP and UDP ports 21, 23 and 25． What types of packets will be permitted by this ACL?
选项 A、FTP
B、Telnet
C、SMTP
D、DNS
E、HTTP
答案D,E
解析 有些常用的公用端口号是我们需要记住的：FTP(20,21),Telnet (23),SMTP-Email(25),DNS(53),TFTP(69),WWW(80),POP邮件(110)。在这，我们过滤了端口号为21,23和25的端口号的流量，因此就是过滤了FTP,Telnet和SMTP的流量，剩下的就是可以允许的。
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