在一台Cisco路由器上执行show access-lists命令显示如下一组信息 Extended IP access list port4444 permit icmp 202.38.97.0,wildcard bits 0.0.0.255 a

admin2019-01-16  25

问题 在一台Cisco路由器上执行show access-lists命令显示如下一组信息
  Extended IP access list port4444
  permit icmp 202.38.97.0,wildcard bits 0.0.0.255 any
  deny icrnp any any
  deny udp any any eq 1434
  deny top any any eq 4444
  permit ip any any
  根据上述信息,正确的access-list配置是(    )。

选项 A、Router(config)#ip access-list extended port4444
    Router(config-ext-nael)#deny icmp any any
    Router(config-ext-nae|)#deny udp any any eq 1434
    Router(config-ext-nac|)#deny tcp any any eq 4444
    Router(config-ext-nac])#permit icmp 202.38.97.0 0.0.0.255 any
    Router(config-ext-nac])#permit ip any any
B、Router(config)#access-list pon4444 permit icmp 202.38.97.0 0.0.0.255 any
    Router(config)#access-list port4444 deny icmp any any
    Router(config)#access-list port4444 deny udp any any eq 1434
    Router(config)#access-list port4444 deny tcp any any eq 4444
    Router(config)#access-list port4444 permit ip any any
C、Router(config)#ip access-list extended port4444
    Router(config-ext-nacl)#permit 202.38.97.0 0.0.0.255 any icmp
    Router(config-ext-nacl)#deny any any icmp
    Router(config-ext-nacl)#deny any any udp eq 1434
    Router(config-ext-nacl)#deny any any tcp eq 4444
    Router(config-ext-nacl)#permit ip any any
D、Router(config)#ip access-list extended port4444
    Router(config-ext-nacl)#permit icmp 202.38.97.0 0.0.0.255 any
    Router(config-ext-nacl)#deny icmp any any
    Router(config-ext-nacl)#deny udp any any eq 1434
    Router(config-ext-nacl)#deny tcp any any eq 4444
    Router(config-ext-nacl)#permit ip any any

答案D

解析 从Extended IP access list port4444可以看出,访问列表采用了扩展配置模式,且访问列表名称为port4444。命令为:ip access-list extended port4444。从permit icmp202.38.97.0,wildcard bits 0.0.0.255 an)可以看出,封禁ICMP协议,只允许202.38.97.0/24子网的ICMP报通过路由器。此外,其他的ICMP报全部禁止通过。命令为:permit icmp 202.38.97.0 0.0.0.255 any;deny icmp any any。从deny udp any any eq 1434;deny tcp any any eq4444;permit ip any any可以看出,禁止了端口为1434的UDP数据包和端口为4444的TCP数据包。命令为:deny Ladp any any eq 1434;deny tcp any any eq 4444。从permit ip any any可以看出,允许所有IP数据包通过路由器。命令为:pennit ip any any,故选择D选项。
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