禁用DNS查找功能
R2(config)#no ip domain-lookup
DNS原理：将域名转换为IP地址
telnet —— 端口号23
ssh —— 端口号22
router(config)#hostname R2
R2(config)#ip domain-name 163.com
R2(config)#crypto key generate rsa
% You already have RSA keys defined named R2.r2.163.com .
% Do you really want to replace them? [yes/no]: yes
The name for the keys will be: R2.163.com
Choose the size of the key modulus in the range of 360 to 2048 for your
General Purpose Keys. Choosing a key modulus greater than 512 may take
a few minutes.
How many bits in the modulus [512]: 1024
% Generating 1024 bit RSA keys, keys will be non-exportable...[OK]
R2(config)#
*?? 1 0:39:4.717: R2(config)#
%SSH-5-ENABLED: SSH 1.99 has been enabled
