原来用 C:WINDOWSsystem32driversetchosts 指定了固定的 DNS，修改后需要

ipconfig /flushdns

刷新 DNS 缓存，使新的 DNS 生效。察看当前 DNS 缓存用

ipconfig /displaydns

ipconfig /? 完整帮助内容如下：

USAGE:

ipconfig [/? | /all | /renew [adapter] | /release [adapter] |

/flushdns | /displaydns | /registerdns |

/showclassid adapter |

/setclassid adapter [classid] ]

where

adapter Connection name

(wildcard characters * and ? allowed, see examples)

Options:

/? Display this help message

/all Display full configuration information.

/release Release the IP address for the specified adapter.

/renew Renew the IP address for the specified adapter.

/flushdns Purges the DNS Resolver cache.

/registerdns Refreshes all DHCP leases and re-registers DNS names

/displaydns Display the contents of the DNS Resolver Cache.

/showclassid Displays all the dhcp class IDs allowed for adapter.

/setclassid Modifies the dhcp class id.

The default is to display only the IP address, subnet mask and

default gateway for each adapter bound to TCP/IP.

For Release and Renew, if no adapter name is specified, then the IP address

leases for all adapters bound to TCP/IP will be released or renewed.

For Setclassid, if no ClassId is specified, then the ClassId is removed.

Examples:

> ipconfig … Show information.

> ipconfig /all … Show detailed information

> ipconfig /renew … renew all adapters

> ipconfig /renew EL* … renew any connection that has its

name starting with EL

> ipconfig /release *Con* … release all matching connections,

eg. “Local Area Connection 1″ or

“Local Area Connection 2″