This is a basic guide on how to join or host a multiplayer server.

(Important note : if the server has any mods running you must enable them from the mod manager before connecting)

It also should be noted that both the host and the connected clients will autosave their own version of the current map whenever a autosave occurs.

The default Factorio port is 34197 (changable in the config) and only uses UDP.

1. Find a server, there are many dedactated servers that are hosted on the multiplayer board on the fourms here: http://www.factorioforums.com/forum/viewforum.php?f=53, Simply find one or you can use Hamachi or Evolve to find the ip and port of your desired host.
2. Simply place the ip and port into the Connect To Game tab under play
3. Press Connect

IMPORTANT : You will need to create your save file before you start the server, as the dedicated server REQUIRES a save file to be provided. This can easily be done by loading up a game in Single-Player and saving it right away.

1. Go to your steam Factorio folder
2. Create a text document and write in it 'Factorio.exe --start-server YOURSAVEGAME.zip' (do not include the '' at each side) (replace YOURSAVEGAME with the name of your savegame name you created above)
3. Save the file as a server.bat (note : The save as type option should read 'all files')
4. Use the server.bat to start the server
5. The console log will be shown in the window
5+. to close the server select the console and press control+c, if you close the window without doing this the game state will not be saved.
6. Forward the ports

Important: There may be no feedback that the server is running except the factorio.exe in the task manager. That means you won't see a window or a console!
This can be changed by adding /wait to the .bat-file, for example:
start /wait Factorio.exe --start-server YOUR_SAVE.zip

This is much quicker and easier than hosting a dedicated headless server.

Simply start Factiorio

1. Go to play, multiplayer, and then new game
2. Choose your desired setup and then press play
3. Your friends can now connect to your server with your ip and port as long as you have your selected port is forwarded.

Due to the fact that I did not create the guide on how to use evolve I am simply placing this link to the guide created on the fourms.

Evolve Guide, Credit to DRBLN : https://forums.factorio.com/viewtopic.php?f=133&t=7714