Hands-on 5: Internet Routes and Measuring Round Trip Times

In this assignment you will get a chance to experiment with two very useful and widely-used network diagnostic tools, traceroute and ping, to expose you to some of the interesting quirks in network routing and packet round trip times.

We recommend, but do not require, that you perform this assignment on Athena. Please note that the TAs cannot guarantee tech support if you do not use an Athena workstation. In either case, make sure you use a workstation on the MIT network. Some results may be quite different if you use an off-campus network.

Measuring Round Trip Times With Ping

In the first two exercises, you will use the ping utility to send echo requests to a number of different hosts. The ping utility is one of the more useful utilities for testing a network. It allows you to measure the time that it takes for a packet to travel through the Internet to a remote host and back. The ping utility works by sending a short message, called an echo-request, to a host using the Internet Control Message Protocol (ICMP). A host that supports ICMP (and most do) and receives an echo-request message simply replies by sending an echo-response back to the originating host.

In many of the exercises, you will be referring to hosts via their DNS names rather than their IP addresses. (For more information about Internet hostnames and DNS, and how these relate to IP addresses, please see Section 4.4 of the course notes.)

For more information about ping, look at the man page on ping and the specifications for ICMP, located in RFC 792. Section 7.4.4 of the course notes describes ICMP as well.

man ping

To use the ping command on Athena, run a command such as:

ping www.google.com

Questions

Now you're ready for this week's questions.

Like before, the questions are in a read-only google doc. Make sure to enter quesitons in the page indicated (please do not erase the question text) and upload them as a PDF to Gradescope. See more detailed instructions at the end of the first week's hands-on. If you are having Gradescope problems, please post a question on Piazza!