Network Simulation

A network simulator written in C that models a local network with switches and stations. Reads topology from configuration files, simulates Ethernet frame forwarding, dynamic MAC address learning, and the Spanning Tree Protocol (STP) to prevent switching loops.

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Coursework. Networking project (SAE) of the BUT Informatique at IUT Robert Schuman, Strasbourg. Written in 2025, over about two months.

Coursework. Networking project (SAE) of the BUT Informatique at IUT Robert Schuman, Strasbourg. Written in 2025, over about two months.

Features

• Topology parsing, reads .lan config files describing switches, stations, and links.
• MAC address learning, switches dynamically build forwarding tables from observed traffic.
• Ethernet frame handling, create, parse, and display Ethernet frames with proper MAC/IP addressing.
• Spanning Tree Protocol, full STP implementation: root bridge election, port roles (Root/Designated/Blocked), loop prevention.
• Forwarding simulation, frames are forwarded, flooded, or dropped based on the learned MAC tables and STP port states.

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Building

git clone https://github.com/mattow02/Projet-Reseaux.git
cd Projet-Reseaux
make

Le binaire est écrit dans out/network_sim. La compilation passe en -Wall -Wextra sans un seul avertissement.

Running

./out/network_sim mylan.lan.txt

Where mylan.lan.txt is a topology configuration file. Several examples are included in the repo (mylan.lan.txt, mylan_no_cycle.lan, w_mylan_1.lan, w_mylan_2.lan).

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Configuration format

A .lan file describes the network topology:

# Define switches and their ports
switch S1 3
switch S2 3

# Define stations
station PC1 aa:bb:cc:dd:ee:01 192.168.1.1
station PC2 aa:bb:cc:dd:ee:02 192.168.1.2

# Define links between devices
link S1:0 S2:0
link S1:1 PC1
link S2:1 PC2

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Project structure

src/
├── main.c              Entry point, loads config, runs simulation
├── config_reader.c/h   Topology file parser
├── network.c/h         Switch tables, MAC learning, frame forwarding
├── stp.c/h             Spanning Tree Protocol implementation
├── ethernet_frame.c/h  Ethernet frame construction and display
├── addresses.c/h       MAC and IPv4 address utilities
└── types.h             Core data types (MAC, IPv4, graph)

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How it works

1. The config file is parsed into an in-memory graph of switches and stations.
2. STP runs to elect a root bridge and assign port roles, blocking redundant paths.
3. Ethernet frames are injected into the network.
4. Switches learn source MAC addresses and forward/flood frames according to their tables.
5. The simulation outputs forwarding decisions and final MAC tables for each switch.