2. 计算机
  3. Refer to the exhibit． The access list has been configured on the S0/0 interface of router RTB in the outbound direction． Which t

Refer to the exhibit． The access list has been configured on the S0/0 interface of router RTB in the outbound direction． Which t

admin2019-04-08  34
问题 Refer to the exhibit． The access list has been configured on the S0/0 interface of router RTB in the outbound direction． Which two packets, if routed to the interface, will be denied?

access-list 101 deny tcp 192．168．15．32 0．0．0．15 any eq telnet
access-list 101 permit ip any any
选项 A、source ip address: 192．168．15．5; destination port: 21
B、source ip address:, 192．168．15．37 destination port: 21
C、source ip address:, 192．168．15．41 destination port: 21
D、source ip address:, 192．168．15．36 destination port: 23
E、source ip address: 192．168．15．46; destination port: 23
答案D,E
解析 这个访问列表定义了两个语句： access-list 101 deny tcp 192．168．15．32 0．0．0．15 any eq telnet access-list 101 permit ip any any在访问列表中匹配的顺序是从上到下，如果匹配了某一句，就退出访问列表，如果没有就一直往下匹配，在访问列表中有一句隐含的拒绝所有。所以不管怎么样都有一句是能被匹配的。在上题中，他定义的第一句是拒绝到从192．168．15．32- 192．168．15．47发出的任何的telnet 的流量，然后第二句定义的就是允许所有的IP流量。而且要明确telnet的流量使用的是端口23,所以这个题的答案就很明确了。
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