[协议分析] 利用PING的RTT测量

billjock

PING程序严格的说是基于TCP/IP协议中的三层与四层之间，利用应用定时器来计算ICMP分组的RTT（往返时间）。程序发送一个ICMP回显请求分组给服务器，服务器紧接着向客户回复一个回显应答分组。客户可以在回显请求分组中将发送时的时钟值作为用户可选数据记录在该分组中，然后服务器会在应答中返回这个时钟值。客户收到回显应答时，它就取当前时钟值计算出RTT，然后打印出来。以下是PING分组的格式\r\n\r\n\r\n

\r\n\r\n\r\n\r\n\r\n\r\n    PING程序允许我们指定分组中可选用户数据的长度，使我们能够测量分组长度对RTT的影响。如果用PING来测量RTT，可选数据的长度必须至少8字节。如果指定的用户数据程度少于8字节，PING也能工作，但不能计算并打印RTT。

ssffzz1

此事如何解释。\r\n\r\n\r\nD:\\>ping -l 0 192.168.1.1\r\n\r\nPinging 192.168.1.1 with 0 bytes of data:\r\n\r\nReply from 192.168.1.1: bytes=0 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=0 time=1ms TTL=255\r\nReply from 192.168.1.1: bytes=0 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=0 time<1ms TTL=255\r\n\r\nPing statistics for 192.168.1.1:\r\n    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\r\nApproximate round trip times in milli-seconds:\r\n    Minimum = 0ms, Maximum = 1ms, Average = 0ms\r\n\r\nD:\\>ping -l 1 192.168.1.1\r\n\r\nPinging 192.168.1.1 with 1 bytes of data:\r\n\r\nReply from 192.168.1.1: bytes=1 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=1 time=1ms TTL=255\r\nReply from 192.168.1.1: bytes=1 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=1 time<1ms TTL=255\r\n\r\nPing statistics for 192.168.1.1:\r\n    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\r\nApproximate round trip times in milli-seconds:\r\n    Minimum = 0ms, Maximum = 1ms, Average = 0ms\r\n\r\nD:\\>ping -l 8 192.168.1.1\r\n\r\nPinging 192.168.1.1 with 8 bytes of data:\r\n\r\nReply from 192.168.1.1: bytes=8 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=8 time=1ms TTL=255\r\nReply from 192.168.1.1: bytes=8 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=8 time<1ms TTL=255\r\n\r\nPing statistics for 192.168.1.1:\r\n    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\r\nApproximate round trip times in milli-seconds:\r\n    Minimum = 0ms, Maximum = 1ms, Average = 0ms\r\n\r\nD:\\>ping -l 128 192.168.1.1\r\n\r\nPinging 192.168.1.1 with 128 bytes of data:\r\n\r\nReply from 192.168.1.1: bytes=128 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=128 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=128 time<1ms TTL=255\r\nReply from 192.168.1.1: bytes=128 time<1ms TTL=255\r\n\r\nPing statistics for 192.168.1.1:\r\n    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),\r\nApproximate round trip times in milli-seconds:\r\n    Minimum = 0ms, Maximum = 0ms, Average = 0ms\r\n\r\nD:\\>