Lab: DNS & Sockets

Introduction

In this lab, you will experiment with the operation of your DNS, Socket, Echo code by using Wireshark to analyze the network packets created by your tools.

Goals

• A real experiment, as I am unsure exactly what you will see.

Acknowledgments

Each team will see different packets and different results, thus the wireshark captures will be different. Hopefully, the questions you are to answer are common.

References

• Course FAQs, Wireshark, Book, etc.

Logistics

Once again you are to continue working as a Pair.

When recording an answer, be sure to also record the question!!!

Preparation

Assignment

Part A: DNS

Do: Fire up Wireshark. Watch your network connection. Setup Wireshark to capture your DNS requests and responses. Think about the parameters to Wireshark.
Do: Using what ever tool you want, flush your DNS cache. I believe the best (only) way you can do this is:
sudo flushdnscache:
This program, written by Tim, flushes you DNS cache. It runs 'sudo', and is the only sudo command you can run and only runs in the Rock Lab.
Do: Use your DNS tool to look up Google or Amazon (because they should return multiple addresses).
Record: Capture the exchange and determine and RECORD how many addresses were returned.
Do: Again, flush your DNS cache, i.e., sudo flushdnscache:.
Do: Use your DNS tool to look up some crazy address that should be in no one's cache...
Record: Capture the exchange and determine and RECORD how many addresses were returned.
Record: When multiple addresses are returned by DNS, How are they delinated in the return info? That is: does the DNS Response packet contain the structure defined for the getaddrinfo library call or does getaddrinfo pull the addresses out of the packet and populated the structure that is returned to the calling program?

Part B: echo

Do: Fire up Wireshark. Watch your network connection. Setup Wireshark to capture your echo packets. Again, determine the Wireshark parameters that are necessary to watch you echo exchange.
Do: Fire up your echo client and your echo server, putting the client on your lab machine and your server on knuth running via a window on your lab machine.
Record: BEFORE capturing any packets discuss with your partner what you will see. Write this up in your lab book. That is, there is echo traffic, but how does that traffic get to the knuth window running on your machine?
Record: Do a few echoes and record what you see?. Make sure that you see the echo exchange AND traffic to the window on your machine.
Do: Fire up your echo client and your echo server, putting the client on your lab machine AND your server on your lab machine.
Record: BEFORE capturing any packets discuss with your partner what you need to do to capture the exchange and again, what you will see. Write this up in your lab book. There is echo traffic, but how does that traffic get to the various windows?

What to Turn-in

• You can turn-in what ever Wireshark captures you want.
• Your lab report should include the Record: sections from above.

Assessment

To earn the equivalent of a B, complete parts A and B.

Mike Erlinger