ip name-server xxxx和ip helper-address xxxx区别

Specifies the address of one or more name servers.

设定name server地址 即指定dns服务器 该命令影响范围只在操作环境 不包括数据流 详见上面链接

ip name-server server-address1 [server-address2...server-address6]

ip helper-address

To have the Cisco IOS software forward User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface, use the ip helper-address interface configuration command.

设定udp广播转发地址 即开启路由器转发包括dns查询在内的8种udp广播报文到指定地址的功能 该命令作用于数据报文 与操作环境无关 详见Clare Gough: Cisco CCNP Routing Exam Certification Guide (Cisco Press) 第57页至58页有关ip helper address说明