Getting Started with SimNet

Ready to dive into your first network security challenge? Don't worry — even if you've never touched a terminal before, you'll be up and running in minutes by following the steps below.

The Example Challenge

This template ships with one canonical example challenge: Ethernet Basics. It demonstrates the minimum viable shape of the DSL v2 schema and walks you through SimNet's packet-observation basics.

When you adopt this template downstream, follow the "Challenge authoring quickstart" steps on the challenges index to add your own challenges, modeled on the example.

Suggestion

Before getting deep into the framework, run through Ethernet Basics end to end so you understand how config.yaml maps to index.md.

Meet Your Workstation

When you open any challenge, the page loads the Simulation Engine. You'll see three main regions — together, they form your network security analysis workstation:

Region	Position (desktop)	Function	Think of it as...
Topology View	Top-left	Renders the network topology — a map of every device and link	A city map: the whole picture at a glance
Traffic Log	Top-right	Streams network packets in real time — who sent what to whom	A highway surveillance camera
Terminal	Bottom	Where you type commands — your main tool	A Linux terminal

The dividers between the three panels are draggable, so you can resize them to whatever ratio feels best.

Tablet and mobile

On a tablet or phone, the interface automatically switches to tabbed mode — use the top tabs or the bottom navigation bar to switch between regions. The features are identical; only the layout differs.

Topology View — Read the Whole Network

The boxes on the topology represent different network devices (PC, Switch, Router, Server). One of them is tagged with a YOU badge — that's your player device.

• Hover any device to see its IP address and MAC address
• Scroll to zoom the topology in and out
• Drag empty space to pan the canvas

Before you start typing commands, take a few seconds to study the topology. Know what's on the network and how it's wired up. That's step one of any security analysis — reconnaissance.

Traffic Log — Watch Packets Flow

Every time a packet crosses the network — whether you triggered it or a device sent it on its own — the Traffic Log updates in real time. You can see each packet's source, destination, and protocol.

• In traffic-analysis challenges, the Traffic Log is your key window into finding the Flag
• In attack and defense challenges, it's how you confirm that an attack actually worked or that a defense held

Terminal — Get Your Hands Dirty

The Terminal is where you actually run commands. You'll see a prompt like this:

simnet@pc1:~$

That tells you you're currently on the pc1 device. Different challenges drop you onto different starting devices.

Important

Some challenges require you to switch to another device — a router or server, for example — using the ssh command before you can complete the task. See SSH Device Switching for details.

Try It Out

Let's walk through the basic workflow using the Ethernet Basics challenge as an example.

1. See What Commands Are Available

simnet@pc1:~$ help

Hit Enter and you'll get a list of every command you can run. Forgot a command? Just type help again — anytime.

2. Check Your Own Network Settings

simnet@pc1:~$ ip addr

This shows your IP address and MAC address — much like checking the Wi-Fi connection info on your phone.

3. Ping Another Device

Find another device's IP on the topology, then use ping to test whether you can reach it:

simnet@pc1:~$ ping -c 3 10.0.0.1

If you get a reply, congratulations — you just sent your first packet. Switch to the Traffic Log and you'll see those packets show up in the list.

4. Capture Packets

simnet@pc1:~$ tcpdump -i eth0 -c 5

This listens on your network interface and stops after capturing 5 packets. Read the packet contents carefully — in some challenges, the Flag is hidden right inside a packet.

5. Submit the Flag

Once you've found the answer, type FLAG{your_answer_here} into the Flag submission box on the challenge page. If it's correct, you'll see a success message.

Tips for Beginners

• Lean on help and --help — Forgot how a command works? Run help to list the commands, then commandname --help for syntax.
• Watch the Traffic Log — Every network command you run in the Terminal shows up as a packet in the Traffic Log. Cross-reference the two and you'll start to grasp how protocols actually work.
• Study the Topology — Look at the map before you act. Once you know the shape of the network, you can reason about where packets should go.
• Don't be afraid to mess up — It's a simulator. Bad commands don't break anything. Experiment freely.
• Up/Down arrows — The Terminal has command history. Press the up arrow to recall previous commands and skip the retyping.

What's Next

You want to...	Go to
Learn every Terminal command	Terminal Command Reference
Learn SSH device switching	SSH Device Switching
Learn about defense tools	Defense Tools
Learn about repair tools	Repair Tools
Jump straight into a challenge	Challenge list