Welcome to the unofficial documentation of FSD, the protocol behind the IVAO and VATSIM online networks.

This documentation was created during the reverse engineering process for FCOM, which forwards messages to a web server. FCOM's implementation of this server forwards it over Discord DM, but it's entirely possible to write a server that does anything it wants (which may or may not involve forwarding) with the forwarded messages.

Note: information may change as new information regarding FSD is discovered. This document is currently heavily focused on VATSIM's implementation (which is much "heavier" than IVAO's), but this will change in the future as I figure out which parts are unique to either network.

Generating the documentation

The documentation is written in Markdown.

To generate webpages with this documentation, use the Python tool MkDocs. It can be installed via pip:

pip install mkdocs
cd fsd-doc


To generate a live "preview" version that auto-refreshes whenever one of the Markdown files is updated:

mkdocs serve

Building the site

To finalize everything into HTML pages:

mkdocs build

Watching FSD in action

To see FSD in action, use Wireshark to monitor traffic on TCP port 6809. Here's a tutorial to get started.

As is the case with anything on the application layer that's in plaintext, FSD can be interacted with over Telnet:

telnet (server address) 6809

IVAO uses eu*.ivan.ivao.aero (replace * with the server number). A list of servers can be found at heartbeat.ivao.aero .

VATSIM uses static IPs. These IPs can be found at any of the URLs starting with url1 at status.vatsim.net. As of the time of writing, two mirrors are available (hardern.net, vroute.net)


Have something you'd like to add to the documentation? Just fork and create a pull request on the GitHub repository.