Master server is a central list of all servers currently hosting network games that have been registered by doomsday. A server admin has the option of advertising their game on the master server. If they choose not to, only computers on the local network will be able to see the game and join.
The master server is located at:
http://dengine.net/master.php
The console variable server-public determines whether a server announces itself to the master.
Due to the project's homepage relocation to dengine.net all versions up to and including 1.8.6 will (by default) be configured with the old master server address. Therefore this address must be updated manually before attempting list or join a game on the master server.