Joining a Multiplayer game
As of version 0.13, players no longer necessarily have to port-forward to play with others. Players may join each other through Steam, or by just the port-forwarded host.
Players wishing to join a game may do so in multiple ways:
- Joining by directly inputting a public IP and port into Factorio.
- Selecting the server from the active public server menu.
- Joining through Steam's services.
- Playing a local LAN game.
Joining by IP
To join a multiplayer game by IP, you will need to know the public IP of a valid server. You can find this through social media, websites, or by word of mouth. After acquiring the IP and port, simply go to play -> Multiplayer -> Connect to server, and provide all the information it asks for.
If the server has been set up correctly to accept public connections, you should be able to join the game.
Joining via server list
Factorio's devs keep a list of all public servers that declare themselves to the service, allowing players to join directly through Factorio. Most of these servers will be password-requiring, but many completely public servers can be connected to. To join via server list, go to Play -> Multiplayer -> Browse public games. Provide your Factorio.com login if asked, and a list of public servers will appear. Simply select one.
Joining through Steam
Steam provides a "game invite" system, simply use that to join. You can find more info about how to use steam in it's documentation. This is the most recommended way for the average player to use multiplayer with their friends, as it allows Steam to handle everything.