《计算机网络-自顶向下方法》第一章18题

Perform a Traceroute between source and destination on the same continent at three different hours of the day.

a. Find the average and standard deviation of the round-trip delays at each of the three hours.

b. Find the number of routers in the path at each of the three hours. Did the paths change during any of the hours?

c. Try to identify the number of ISP networks that the Traceroute packets pass through from source to destination. Routers with similar names and/or similar IP addresses should be considered as part of the same ISP. In your experiments, do the largest delays occur at the peering interfaces between adjacent ISPs?

d. Repeat the above for a source and destination on different continents.

Compare the intra-continent and inter-continent results.

Tracert(跟踪路由)是路由跟踪实用程序,用于确定 IP数据包访问目标所采取的路径。Tracert 命令使用 IP 生存时间 (TTL) 字段和 ICMP 错误消息来确定从一个主机到网络上其他主机的路由.

注意:

  1. 每次发送后的回应数据包TTL加1,与ping时TTL的递减相反。
  2. 对每台路由器测试三次。
  3. 通过加入-d参数,减少将中间IP地址通过查询DNS解析为名称,加速显示结果。
  4. 加入-m指定最大跃点数量,-w指定ICMP超时时间

在macOS和Linux中使用traceroute命令。

traceroute -m 30 -w 2 www.sysu.edu.cn

1

平均往返时延:(3.4+9+2.8)/3=5.067ms

方差:7.79556ms

共有17个路由器,ISP数量为2

在从广州电信到广州教务网的对等接口上出现最大时延。

traceroute -m 30 -w 2 www.mit.edu

2

平均往返时延:(55.8+55.7+55.6)/3=55.7ms

方差:0.00667ms

共有11个路由器,ISP数量为3

在从广州电信到上海电信和从上海电信到东京电信的ISP的对等接口上出现较大的时延。