Networking challenges

These are the hands-on challenges for the Networking course. You build small networks inside your own laptop, break them, and read what happens.

You do not need a second computer. You do not need a router. The lab is a Linux machine that runs inside Docker on your laptop. Everything you build lives inside it. When you type exit, it is gone, and your real network is untouched.

This repository is a template. Copy it to your own GitHub account first (the green Use this template button), then clone your copy.

Two places to type commands

You will type commands in two places. Every command block in a README says which one.

Label	Where	How you know
On your computer	Your normal terminal (Git Bash, PowerShell, Terminal)	Your usual prompt
In the lab	The Linux machine inside Docker	The prompt starts with (lab)

Your real addresses, your router and the internet path are on your computer. The networks you build are in the lab.

Start the lab

1. Install Docker Desktop and start it. Read Docker's own page for what your computer needs: https://docs.docker.com/desktop/

2. On your computer, open a terminal inside this repository folder.

3. Start the lab:

   Your computer	Command
   Windows with Git Bash, macOS, Linux	bash lab/start.sh
   Windows with PowerShell	.\lab\start.ps1

4. The first time, it builds the lab image. After that it starts fast.

5. You should see a prompt that starts with (lab). Your repository folder is there as /work.

6. Leave the lab with exit.

The lab uses docker run --privileged. That gives the lab container wide power over Docker's own virtual machine. We need it so you can make virtual networks. Use it only for this lab image.

Challenges

#	Folder	Parts	You will
0	challenges/challenge-0-setup	1 install, 2 your numbers	Start the lab, pass the setup checker, and read your own network numbers
1	challenges/challenge-1-two-computers	1 virtual cable, 2 wrong mask	Make two computers talk, capture it, then make them disagree
2	challenges/challenge-2-router	1 two subnets and a router	Build a router between two networks, make a ping cross it, and see which addresses change
3	challenges/challenge-3-conversation	1 listening and the handshake	Run a server on two listening addresses, capture the handshake, and read both sides with ss
4	challenges/challenge-4-home-router	1 masquerade, 2 forwarding and a guest network	Put devices behind a router with NAT, read the NAT table, forward a port, and keep a guest away from home
5	challenges/challenge-5-dhcp-dns	1 leases and names	Make the router hand out addresses and names with dnsmasq
6	challenges/challenge-6-capstone	1 addresses and routes, 2 NAT, forwarding and isolation, 3 DHCP and DNS, 4 break and fix	Build a whole small internet from your own scripts, then find three faults that a script injects

Part 2 of the course, "Beyond your home network":

#	Folder	Parts	You will
7	challenges/challenge-7-bgp	1 three networks, 2 read and withdraw, 3 backup link, 4 hijack and filter	Run three networks that talk BGP, watch a route appear and disappear, add a backup link with your own preference, then steal a block and stop it
8	challenges/challenge-8-vpn	1 office and café, 2 the tunnel, 3 what each side sees, 4 full and split tunnel	Build a WireGuard VPN between two networks behind NAT and prove with captures what each network sees
9	challenges/challenge-9-toolbox	0 the broken network, 1 Wireshark, 2 tcpdump, 3 mtr, 4 dig, 5 nmap, 6 iperf3, 7 curl	Find four hidden faults in a broken network, one tool at a time, and save the evidence

More challenges are added as the course goes on.

How much help you get changes as the course goes on:

Challenges	Help
0 and 1	Guided. Every command is typed by you, one at a time, and every line is explained
2, 3, 4 and 5	Gapped. The script is nearly complete. A few lines are missing and marked TODO. The test tells you which gap is wrong
6	Open with hints. You get the goal, the tests and a ladder of hints. You write the scripts, starting from your own earlier ones
7, 8 and 9	Guided, then gapped. The first part of each is guided; the later parts have TODO gaps. Challenge 9 asks you to choose the tool yourself in its last round

Each part is a folder with the same files:

File	What it is
README.md	Words to know, what you build, the steps, and where each number comes from
One script	The commands, with comments. You can run it, or type its lines one by one. In challenges 2 to 5, some lines are gaps for you to fill. In challenge 6 you write it
results.md	Your own output. You fill this in and commit it
test.sh	Run it in the lab. It says PASS or FAIL for each check. When a check fails, read its message: it names the gap or the thing to look at

Run a test from the lab like this:

bash challenges/challenge-0-setup/part-1-install/test.sh

Scripts are safe to run again. Each one deletes what it built before it starts.

If something is wrong

Run the setup checker in the lab:

bash toolkit/check-setup.sh

It prints one line per check. Read the first FAIL line. The word after FAIL is the name of the problem, and the rest of the line is the fix.

Name	Meaning
not-in-lab	You are not inside the lab. Start it with lab/start.sh
no-privilege	The lab was started without --privileged. Start it with lab/start.sh
wrong-image	A tool is missing. Your lab image is old or wrong
crlf-line-endings	A script has Windows line endings. The checker prints the fix
repo-not-visible	Your repository folder is not at /work. Start the lab from inside the repository

If you are stuck on a part

Some parts build on the part before. If you are stuck, you can build the network from the end of an earlier part and keep going. Run this in the lab:

bash /work/toolkit/restore.sh --list
bash /work/toolkit/restore.sh 4.1

The first line lists the parts you can restore (2.1, 4.1, 4.2, 6.1, 6.2 and 6.3) and what each one builds. The second builds the network from the end of challenge 4, part 1. A restore changes only the lab network. It never changes your own files.

The restore builds in toolkit/restore/ are the course's own answers. Read them after you have tried, not before. If you used one, say so in your capstone demo.

What is in each folder

Folder	Contents
lab/	The lab image recipe (Dockerfile) and the start scripts
toolkit/	Shared helpers (lib.sh), the DHCP lease script (udhcpc-hook.sh), the setup checker (check-setup.sh) and the restore script (restore.sh, which runs the builds in toolkit/restore/)
challenges/	One folder per challenge, one subfolder per part

Line endings

Windows saves a new line as two characters. Linux wants one. A script with the Windows kind stops with strange errors. This repository has a .gitattributes and an .editorconfig that keep scripts in the Linux kind. If a script still has the Windows kind, the checker tells you the command that fixes it.