1.no ip domain-lookup
这个命令必须要在global config 模式下才能执行
为的是避免这样的错误

% Unknown command or computer name, or unable to find computer address

Router>
Router>baidu
Translating "baidu"...domain server (255.255.255.255)
% Unknown command or computer name, or unable to find computer address

Router>enable
Router#google
Translating "google"...domain server (255.255.255.255)
% Unknown command or computer name, or unable to find computer address

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#no ip domain-lookup
Router(config)#google
               ^
% Invalid input detected at '^' marker.

Router(config)#exit
Router#
%SYS-5-CONFIG_I: Configured from console by console

Router#baidu
Translating "baidu"
% Unknown command or computer name, or unable to find computer address

Router#exit

这样在随意输入一个字符串以后，路由器就不会去解析域名，而把输入的字符串当作一个命令去处理

Router#baidu
Translating "baidu"
% Unknown command or computer name, or unable to find computer address