Enter the network name, password and click "Create".

Step 2: Ask your friends to join the network
Send your friends the name of the Radmin VPN network and the password to join to this network.

Step 3: Run Left 4 Dead 2

Step 4: Add the game to the firewall exceptions
You need to add rules to the firewall. Open Radmin VPN -> System -> Firewall Exceptions and add "left4dead2.exe" to the exceptions.

Step 5: Enable the "Developer Console"
Go to the game main menu and click "Options". Click "Keyboard/Mouse". 

Click "Allow Developer Console" and set "Enabled".

Step 6 (optionally): Automatic detection of LAN games
You can also enable automatic detection of LAN games for convenience of friends who want to join your game. To do this you need to click "Options" at the game main menu. Than click "Multiplayer". Click "Automatically Discover LAN Games" and set "Enabled".

Step 7: Create Left 4 Dead 2 LAN game
1. Open the "Developer Console" by pressing "~" on your keyboard (its the key below Esc).

2. Type in the console "sv_lan 0" and press "Enter".

3. Type in the console "sv_allow_lobby_connect_only 0" and press "Enter".

4. In the console type "map" then press "Space". All playable maps will be shown.

5. Use the arrow keys on your keyboard to navigate to the desired map. Press "Enter".

General command to create a local game is: "map mapName gameMode"

List of all maps:

• Dead Center: "c1m1_hotel", "c1m2_streets", "c1m3_mall", "c1m4_atrium"
• The Passing: "c6m1_riverbank", "c6m1_port", "c6m2_bedlam"
• Dark Carnival: "c2m1_highway", "c2m2_fairgrounds", "c2m3_coaster", "c2m4_barns", "c2m5_concert"
• Swamp Fever: "c3m1_plankcountry", "c3m2_swamp", "c3m3_shantytown", "c3m4_plantation"
• Hard Rain: "c4m1_milltown_a", "c4m2_sugarmill_a", "c4m3_sugarmill_b", "c4m4_milltown_b", "c4m5_milltown_escape"
• The Parish: "c5m1_waterfront", "c5m2_park", "c5m3_cemetery", "c5m4_quarter", "c5m5_bridge"

List of all gameModes: "campaign", "mutation", "realism", "scavenge", "survival", "versus".

Default gameMode is a "campaign" with normal difficulty. To choose another gameMode, type the desired gameMode after the mapName in the console (example: "map c1m4_atrium realism").

Game client setup

Step 1: Install Radmin VPN and connect to the network
Download and install Radmin VPN. In the main Radmin VPN window, click "Join Network". Enter the Network Name and Password and click "Join". 

Make sure you and your friends are on the same network.

Step 2: Run Left 4 Dead 2

Step 3: Add Rules to the Firewall
You need to add rules to the firewall. Open Radmin VPN -> System -> Firewall Exceptions and add "left4dead2.exe" to the exceptions.

Step 4: Join the game
When the game is created and "Automatically Discover LAN Games" is enabled, your game may appear in the main menu. And your friends can use it to join your game.

Alternative way is open the "Developer Console" by pressing "~" on your keyboard (its the key below Esc) and type there the command to join "connect gameIP" (example: "connect 26.12.125.71:27015").

Troubleshooting

If you can't see your friends or any servers in the game:
1. Make sure you all have the same game version.
2. Make sure you did all the steps in the instruction above.
3. Make sure you added the game to the firewall exceptions.