BadLink

Network condition testing tool for Windows. Deliberately degrade your network to test how applications handle poor connectivity. Inspired by Clumsy but built with performance, control & customization in mind.

Features

BadLink intercepts network packets at the kernel level using WinDivert and can simulate various network problems:

Feature	Description	Range/Options
Packet Loss	Drop random packets	0-100%
Latency	Adds a fixed delay to packets	0-5000 ms
Bandwidth Limiting	Uses token bucket throttling to limit bandwidth	56kbps to 100Mbps
Packet Duplication	Clone Packets	1-5 copies
Out of Order Delivery	Shuffle packet order	Configurable gap
Jitter	Adds a variable delay to packets	Separate min/max ms

Screenshots:

Built with

Written in C++ using Visual Studio 2022 IDE with C++ Desktop Development

• WinDivert 2.2 for the packet interception driver
• imgui + DirectX 12 for the UI and hardware rendering
• tomlplusplus for the configuration file

Requirements

• Windows 10/11 (64/32-bit)
• Administrator privileges (required by WinDivert driver)
• Visual C++ Redistributables 2022
• DirectX 12 compatible GPU

Building from source

Requirements:

• Visual Studio 2022 with C++ Desktop Development
• Windows SDK 10.0+

git clone https://github.com/pagewalk/badlink.git
cd badlink
# Open BadLink.sln in Visual Studio 2022
# Build in Release x64

Dependencies

All dependencies are included in the external/ folder:

• WinDivert 2.2.2 driver, libraries and headers
• imgui with DirectX 12
• tomlplusplus header-only library

Usage

1. Run badlink.exe as Administrator
2. Configure network conditions in the GUI:
   • Enable desired conditions (latency, loss, etc.)
   • Set parameters for each condition
   • Choose direction (inbound/outbound/both)
3. Set WinDivert packet filter (default "true" captures all)
4. Click "Start Capture" or use configured hotkey
5. Your network will behave as configured
6. Click "Stop Capture" to restore normal network

Preset Filters

Filter	Description	Use Case
true	All traffic	Capture everything
tcp	Only TCP packets	TCP protocol analysis
udp	Only UDP packets	UDP protocol analysis
udp.DstPort == 53	Only DNS queries	DNS monitoring/blocking
ip.DstAddr >= 192.168.0.0 and ip.DstAddr <= 192.168.255.255	Local network only	LAN traffic isolation
tcp.DstPort == 443	HTTPS traffic only	SSL/TLS traffic filtering
outbound	Only outgoing traffic	Monitor outbound connections
inbound	Only inbound traffic	Monitor inbound connections

See WinDivert Filter Language for full syntax and how to construct your own filters.

Configuration

BadLink saves settings to a badlink.toml file in the applications current directory, these settings include:

• WinDivert specific parameters (queue size, timeout, etc.)
• Performance tuning (worker threads, batch size)
• Filter presets
• Hotkey configuration

Known Issues

• Some games anti-cheat systems can flag the WinDivert driver
• Requires admin privileges (WinDivert limitation)
• Windows Defender may flag as suspicious (packet interception behavior)
• WinDivert issues and limitations can be found here: WinDivert: Known Issues

Third-party libraries

This project includes the following third-party libraries in the external/ folder:

• WinDivert - LGPL v3 or GPL v2 © basil
  Windows kernel driver for packet capture/injection
  https://github.com/basil00/Divert

• Dear ImGui - MIT License © Omar Cornut
  Immediate mode graphical user interface
  https://github.com/ocornut/imgui

• tomlplusplus - MIT License © Mark Gillard
  Header-only TOML parser and serializer
  https://github.com/marzer/tomlplusplus