国外DNS比较（建议用GOOGLE DNS：8.8.8.8、8.8.4.4）

GOOGLE DNS：8.8.8.8、8.8.4.4、4.2.2.2
OPENDNS：208.67.222.222、208.67.220.220

测评如下：
Ping statistics for 8.8.8.8:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 56ms, Maximum = 59ms, Average = 57ms

Ping statistics for 8.8.4.4:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 45ms, Maximum = 49ms, Average = 46ms

Ping statistics for 4.2.2.2:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 242ms, Maximum = 242ms, Average = 242ms

Ping statistics for 208.67.222.222:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 259ms, Maximum = 263ms, Average = 261ms

Ping statistics for 208.67.220.220:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 252ms, Maximum = 264ms, Average = 259ms

优选：8.8.8.8、8.8.4.4！