NET-Simulator

An educational virtual computer network simulator for lecturers and students learning the basics of computer networks.

Overview

NET-Simulator lets students build virtual networks in a virtual environment. It supports four kinds of virtual devices — router, desktop computer, switch, and hub — wired together with universal cables and controlled through a command-line interface that mimics real network gear. The simulator implements layers 1–3 of the ISO/OSI model.

Features

Network protocols

• Restricted IPv4 implementation (RFC 791)
• ARP service with broadcast requests to resolve IP-to-MAC bindings
• Restricted ICMP (RFC 792) supporting ping and traceroute
• Ethernet-like layer-2 protocol with 6-byte MAC addressing, auto-assigned by the simulator kernel

Virtual devices

• Router — layer-3 commutator with 8 IPv4 interfaces; forwards packets per a static routing table
• Desktop — a router with a single interface
• Switch — layer-2 commutator with 8 ports; uses MAC-learning like a real Ethernet switch
• Hub — 8-port broadcast device with no forwarding logic
• Cables — universal links with no physical characteristics and infinite bandwidth; they blink when transmitting

GUI

• Drag-and-drop devices on the virtual desktop
• Per-device context menus; double-click a device to open its virtual console
• Command history (Up/Down), Ctrl+L to refresh, Ctrl+C to abort
• Export the current network to an HTML report with a PNG diagram via a user-customizable XSLT template (cfg/tohtml.xsl)

Project files are XML, validated against src/main/resources/dtd/netsimulator.dtd.

Requirements

• Java 21 (JRE to run; JDK to build from source)
• Apache Maven 3.x to build from source

Avoid installing into a path that contains non-ASCII characters — the JVM may fail to read configuration files. See public_html/en/install.shtml for details.

Build from source

mvn package

This produces a shaded fat JAR at target/netsimulator.jar plus a distribution archive under target/ (built via the Maven Assembly plugin).

Run

On Linux/macOS:

./run.sh

On Windows:

run.bat

Both scripts launch netsimulator.jar with cfg/logging.properties as the logging config. On first launch the app opens xml/test.xml — a sample network with 4 desktops, 1 router, and 1 switch.

Quick start

1. Run ./run.sh (or run.bat). The bundled xml/test.xml opens.
2. Double-click any computer to open its virtual terminal.
3. Try ifconfig to see the configured interfaces, then ping 12.0.0.11 from Desktop 1 to send ICMP across the router to Desktop 5.
4. Type help for the full command list.

CLI reference

Command	Synopsis	Description
help	help [-h]	Display the reference guide.
ifconfig	ifconfig [-h] [-a] [<interface>] [<address>] [-broadcast <address>] [-netmask <address>] [-up|-down]	Configure a network interface, or show interface info.
route	route [-h] [{-add|-del} <target> [-netmask <address>] [-gw <address>] [-metric <M>] [-dev <If>]]	Manipulate the IPv4 routing table; without options, prints it.
ping	ping [-h] [-i <interval>] [-t <ttl>] <destination>	Send ICMP echo to check accessibility of an interface. Ctrl+C aborts.
arp	arp [-h] [-r <IP-address> <interface>]	Show the ARP table; -r resolves a MAC for a given IP via a request.
mactable	mactable [-h]	Show the MAC-address table (switch-specific).

Pass -h to any command for its full help. Shell shortcuts: Up/Down navigate history, Ctrl+L refreshes the screen, Ctrl+C aborts the running command.

Project layout

src/main/java/org/netsimulator/
├── Netsimulator.java   entry point (main)
├── gui/                Swing UI: MainFrame, NetworkPanel, device shapes, dialogs
├── net/                simulation core: devices, packets, routing, ARP, ICMP, addresses
├── term/               virtual terminal and CLI command implementations
└── util/               misc utilities (ID generator, etc.)

Runtime resources live under cfg/ (logging, XSLT export template, default config) and xml/ (sample projects).

License

NET-Simulator is licensed under the GNU General Public License v2 — see COPYING for the full text.

Links

• Upstream repository: https://github.com/checkpoint20/net-simulator
• Issue tracker: https://github.com/checkpoint20/net-simulator/issues