C:\WINDOWS>ping -f -l 1500 127.0.0.1
Pinging 127.0.0.1 with 1500 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Ping statistics for 127.0.0.1:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
上面的式子中,-l 是 L 的小写(不是 1 喔),1500 是我们要测的 MTU 值,结 果出现了 Packet needs to be fragmented but DF set. 这个东西,那表示MTU值 太大了,你需要更小的 MTU 值才行!好啦!那假设我们使用 1464 来测试时:
C:\WINDOWS>ping -f -l 1464 127.0.0.1
Pinging 127.0.0.1 with 1464 bytes of data:
Reply from 127.0.0.1: bytes=1464 time=10ms TTL=128
Reply from 127.0.0.1: bytes=1464 time<10ms TTL=128
Reply from 127.0.0.1: bytes=1464 time<10ms TTL=128
Reply from 127.0.0.1: bytes=1464 time<10ms TTL=128
Ping statistics for 127.0.0.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 10ms, Average = 2ms
结果出现了回应了!这表示这一个 MTU 值是可行的!不过,强烈建议找出可行的 最大 MTU 值!这样一来,在设定的时候,才可以达到最佳的网速!
找出 MTU 值:利用上面这个方法找到的数值还不是 MTU 喔!由于一些封包上面的 问题,上面这个值再加上 28 才是我们所需要的 MTU 值!所以,在上面的例子 中,我们所需要的 MTU 值是 1464+28=1492!