traceroute

Linux 默认以 UDP 为探测协议（利用 TTL，初始时把 TTL 设置为 1，路由器向源地址发送 ICMP 超时报文），会看到很多星号，因为很多网络设备并不会对 UDP 作出回应。所以我们加上 -I 改成 ICMP 协议做探测后，网络设备就有回应了。注意 Windows 默认以 ICMP 为探测协议。

$ traceroute  www.baidu.com
traceroute to www.a.shifen.com (180.101.49.12), 64 hops max
  1   10.0.2.2  0.133ms  0.131ms  0.087ms
  2   192.168.1.1  3.048ms  1.466ms  1.574ms
  3   100.65.0.1  8.975ms  3.067ms  6.472ms
  4   61.152.53.149  5.644ms  3.691ms  4.624ms
  5   61.152.24.226  5.357ms  4.393ms  4.244ms
  6   202.97.29.122  10.171ms  10.403ms  8.755ms
  7   58.213.94.118  10.707ms  11.880ms  11.441ms
  8   58.213.94.90  9.644ms  *  *
  9   58.213.96.110  12.758ms  12.095ms  11.842ms
 10   *  *  *
 11   *  *  *
 12   *  *  *
 13   *  *  *
 14   *  *  *
 15   *  *  *
 16   *  *  *
 17   *  *  *
 18   *  *  *
 19   *  *  *
 20   *  *  *

$ traceroute  www.baidu.com -I
traceroute to www.a.shifen.com (180.101.49.12), 64 hops max
  1   10.0.2.2  0.099ms  2.363ms  0.078ms
  2   192.168.1.1  3.320ms  1.220ms  1.204ms
  3   100.65.0.1  8.737ms  4.872ms  6.403ms
  4   61.152.54.125  5.035ms  3.397ms  4.288ms
  5   *  61.152.25.110  4.176ms  *
  6   202.97.101.30  7.447ms  6.399ms  5.936ms
  7   58.213.95.110  10.488ms  *  9.014ms
  8   *  58.213.95.134  11.064ms  *
  9   58.213.96.74  10.997ms  10.042ms  10.592ms
 10   *  *  *
 11   *  *  *
 12   *  *  *
 13   180.101.49.12  11.269ms  9.518ms  8.779ms

traceroute 也有一个明显的不足：它不能对这个路径做连续多次的探测，可以用 mtr 取代。