I want to host a server on my computer to play with my friends over the Internet. What do I need to do to allow my friends to connect to me?

In order for users outside your local network to connect to a server hosted on your computer, you must properly configure your network, security software, and the game so that connection requests can reach your computer.

Setting Up Your Connection

Some of the following steps may not apply to you, for example if you do not have a router and your computer is connected directly to your modem—if the step does not apply, skip the step and continue with the next one.

You will need your public Internet IP address. This can be viewed quickly by visiting a site like whatismyip.com. This address identifies your connection to the Internet, similar to how a street address identifies your house.

1. Configure your firewall
   You will need to set your firewall to allow unsolicited incoming connections for the game you intend to host. If you are unsure how to do this, please refer to the manual or contact the support provider for your firewall software, or temporarily disable your firewall for the duration that you host the server.
2. Configure your router
   Forward port 27015 on both TCP and UDP protocols. If you specify an alternate port when creating the server, forward that port instead of port 27015.
   
   For guided instructions on forwarding a port for a large selection of home routers, please visit portforward.com and select the router model you have, or that best matches the one you have. Select "Half-Life 2 Steam Server" when you reach the list of applications.
3. Start the game and create a local server
   NOTE: some of the following steps require that you enter commands into the console. If you require assistance with enabling and/or using the console, please see the Console article.
   
   
   1. Open the game and click the menu option to create a local server (typically "Create Server")
      • Note: Left 4 Dead and Left 4 Dead 2 do not feature a menu option to create a local server. Instead, you need to use the Console for the game and enter the map mapname command, where mapname is the name of the map file you want to start on. To get a list of map files, type the maps * command.
   2. Configure the server as you prefer, then start the game.
   3. Type the following commands into your console:
      
      
      • sv_lan 0
      • ip [your IP address] (replace [your IP address] with the public IP address you recorded initially, so you have a command that looks like ip 255.255.255.255)
   4. You may need to enter the heartbeat command after entering these commands in order to update your IP address with the Steam master servers. If people viewing your server still see Server is not responding, then please enter the map mapname command, where mapname is the name of the map file you want to start on. To get a list of map files, type the maps * command.

Once you have completed these steps, users should be able to join your currently running game. You will need to repeat the in-game steps if you exit the game.