Since OpenTTD 12.0 multiplayer update released port forwarding is no longer needed. Just start a server and ask your friends to join, OpenTTD team will take care of the rest :)

1. From the Main Menu, click Multiplayer
2. Click Start Server
3. Pick a name for your game to help others identify it, and enter it into the Game name box
4. Configure the additional settings:

• Set Password sets a password for the server so that only users who know the password can join your game.

• Connection specifies whether the server is for local/private use only, or advertises itself to the master server so it is visible in the internet server list.

• Language Spoken is for requesting that users speak a certain language on your server.

• Max clients limits the total number of clients (players and spectators) that can connect.

• Max companies limits the number of companies at game.

• Max spectators limits the number of clients who can connect to watch but not play (not-players).

5. Click New Game (to generate random new game), or Load Game (to continue an saved game), or Play Scenario, or Play Heightmap.

Players connected to your home network should immediately see your server on the server list and be able to connect easily.

If some players are connecting via the public Internet, however, your server will only appear if you have chosen "Internet (advertise)" under "Connection" (there may be a delay of several minutes before it is visible). Otherwise, they will need to know your router's IP address, or your computer's if you aren't using a router. This can be obtained by visiting https://www.whatismyip.com/.

For your safety, do not disable your firewall entirely. Instead, configure it to allow UDP and TCP connections to port 3979. If you want your server to be visible on the public server list as well (recommended), you will also need to open port 3978 to UDP connections only.

If you are connecting to the Internet through a router you will need to tell the router to send game data from players outside of your home network to the computer that will be running your OpenTTD server. Else, the data will simply be discarded before it ever reaches the server. In this case, UDP and TCP connections to port 3979 will need to be forwarded. (If you can't use port 3979 for some reason, you can make OpenTTD use another port by entering "server_port <number>" into the game's console.)

If you want your server to be visible on the public server list (recommended), you will also need to forward UDP connections to port 3978.

There is a simple solution to avoid port forwarding tho. Just plug your Ethernet cable directly into PC and everything should work.
If you can't do that then follow the steps below to set up port forwarding:

1. Go to your routers setting. ( http://192.168.0.1/ or http://192.168.1.1/ )
2. Enter the login and password. ( Usually it's admin/admin )
3. Find the DHCP clients list and copy your PC mac adress.
4. Reserve the local IP ( for example 192.168.0.100 ) for your mac adress. You might need to reload the router afterwards.
5. Find the Port forwarding/Virtual servers tab and add the new rule.
6. Enter the service port ( 3979 for OpenTTD ) and local IP adress you just reserved for your PC. Choose both TCP and UDP connections and save the rule.
7. Make another rule for port 3938 ( UDP only ) if you want your server to appear on the OpenTTD site.
8. Reload the router

Note that you wont be able to host the server if you have a private IP. To check if it's private you should compare your WAN IP adress from router settings and the one from https://www.whatismyip.com/ .
If it's different then your IP is private and you should contact your internet provider to buy a public one. You can still host a local server using Hamachi to play with your friends only.

If you're planning on playing with your friends only or you can't set up port forwarding correctly then there is a method easier than that. You and your friends will need to install Hamachi. I'll explain how to do it, just follow the steps below:

1. Go to vpn.net.
2. Download and install Hamachi.
3. Launch Hamachi and click the Blue power button.

4. Create a Hamachi account if you don't have one already.
5. Press "Network".
6. Press "Create new network".
7. Enter the Network ID ( It's a Hamachi server name, could be anything but has to be unique ).
8. Enter the Password for your Hamachi server and press "Create"
This is all you have to do as a host. Now your friends should connect to Hamachi server you just created. This is how:

1. Download and install Hamachi, create an account.
2. Press "Network".
3. Press "Join the existing network".
4. Enter the Network ID and Password.
5. Press "Join"

Now the host can create an OpenTTD server.
In case to connect to it your friends should open the console in game (Press "~") and type connect <IP:Port>. IP is hosts IPv4 adress from Hamachi, Port should be 3979 if you didn't change it. So the command should look like this - connect 25.70.101.69:3979.

If you are expecting many players and aren't going to be using the computer running the server to play yourself, you can start OpenTTD as a Dedicated server instead of the usual interactive graphical version.

A dedicated server is a OpenTTD network game Server that does not have a local client taking part in the game. A dedicated server can run in the background on a computer.

Method 1:

• Create a shortcut to openttd.exe

• Right-click on the shortcut and click Properties

• Add -D onto the end of the Target line

• Click Apply

• Run the shortcut

Method 2:

• On the start menu click Run

• Enter: "c:\(path to openttd)\openttd.exe" -D

• Click OK

There are 3 ways to change the game options:

• Launch a single player game, change the settings, and close the game.

• Use the console commands to control the server while it is running.

• Edit the Openttd.cfg file manually.

Change the network settings in the Network section of Openttd.cfg:

• Set Lan internet to 0.

• Change Server name so you can identify the server,

• Set Server advertise to true, so it will be visible on the Server list

Configure the dedicated server to accept rcon commands:

• In the dedicated server window, type rcon_pw <password>.

Example: rcon_pw x8na7f

Connect to the server as a client:

• Launch OpenTTD normally.

• Find your server on the multiplayer list and connect to it.

• Open the console (~ key).

• Type rcon <password> "<command>".

Example: rcon x8na7f "kick 5"

In the dedicated server window (or with rcon):

• Type ls to list the files of the current directory, a number will be beside each one, which represents <number> below.

• Type cd <number> to go to that directory.

• Type load <number> to load that file.

• You can also load savegames and scenarios with the -g "<filename>", command line option.

Example: openttd.exe -D -g "scenario/echo.scn".

If you do not want to run docker: Run your dedicated server in ubuntu/debian you can download and install a init.d script You will get the following functions:

• Automatically startup when your server box bootup

• Automatically shutdown when you server box is shutdown

• Automatically saving your game at a defined interval

For more functions, install guide and download, visit: https://bitbucket.org/frodus/openttd-init