Project 1: Setup

Operating System Installation

This project has been tested to work on Linux and Mac.

If you’re on Windows, you need to install Windows Subsystem for Linux (WSL). WSL is a tool which allows you to run a Linux environment directly on Windows. To install WSL,

  1. Open PowerShell as Adminstrator, then run wsl --install. This should install the Ubuntu distro. When prompted, restart your computer.
  2. Open the Ubuntu terminal from the Start Menu. It should prompt you to choose a username and password. Choose whatever you like and remember it.

If the installation was successful, you should see username@hostname:~$ in your terminal. If you are using VSCode, you can click on the “><” arrows in the bottom left corner and select “Connect to WSL” to open a Linux environment. Other code editors might also have options to connect to WSL.

Note on File Location (Windows Users)

After downloading the starter code (see below), do not run Linux commands on files located in the Windows filesystem (those under /mnt/c). This can be frustratingly slow because you are running Linux commands on the Windows disc. Instead,

  1. Create a project directory in your WSL home using mkdir -p ~/projects.
  2. Copy the extracted starter code into ~/projects using cp -r /mnt/c/Users/<username>/Downloads/cs168-su25-proj1-traceroute ~/projects/. You can also drag the folder into the Explorer sidebar tab if you are using VSCode.
  3. Navigate to the folder in your terminal using cd ~/projects/cs168-su25-proj1-traceroute and work from there.

Python Installation

This project has been tested to work on Python 3.11. (It probably works on newer versions of Python as well, but use at your own risk.)

If you run python3 --version or python --version in your terminal and you see output of the form Python 3.11.*, you’re all set.

Starter Code

Download a copy of the starter code here.

In your terminal, use cd to navigate to the cs168-su25-proj1-traceroute directory. All of the Python commands should be run from this directory.

To check that your setup works, in your terminal, run:

sudo python3 traceroute.py cmu.edu

If you see something like this, everything should be set up correctly:

traceroute to cmu.edu (128.2.42.10)
 1: *
 2: *
 3: *
(some lines omitted...)
26: *
27: *
28: *
29: *
30: *

You should only edit traceroute.py. There are comments clearly indicating the places where you should fill in code.

Guidelines:

  • Don’t modify any other files.
  • Don’t add any new files.
  • Don’t add any imports.
  • Don’t edit any code outside the sections indicated by the comments.
  • Don’t add any hard-coded global variables.
  • Adding helper methods is fine (and encouraged).
  • In general, if we haven’t told you to use something, you probably don’t need it. Our goal is not to trick you!

New Spec

Note: This spec has been rewritten for Fall 2024 to be clearer and provide a few extra hints. It may contain bugs.

If you would like to work off the previous version of the spec, you can find it here.

Spec changelog:

  • [Aug 29] Guide: ICMP checksum is 16 bits, not 8 bits.
  • [Sep 2] Guide: The ICMP payload contains a copy of the header of the original packet (UDP-over-IPv4) that triggered the error. It does not contain a copy of the payload of the original UDP-over-IPv4 packet.
  • [Sep 2] Guide: Added suggested reference materials.
  • [Sep 2] Test B7, Irrelevant UDP Response: The “Port Unreachable” message is ICMP-over-IP. It is not UDP-over-IP.
  • [Sep 4] Stage 1, Manual Traceroute: As seen in the starter code, there’s a range of destination port numbers you can use, not just a single one.
  • [Sep 4] Test B16, Irrelevant TTL Response: Clarified what the previous traceroute probe was doing.
  • [Sep 4] Stage 1, Manual Traceroute: Clarified some weird router behavior with endianness.
  • [Sep 19] Test B13, Duplicate Responses: Added some tips.