Some old games can only be played over LAN. There are multiple ways to do this, including GameRanger.
However, GameRanger does not support all games, such as COD: WAW. Lets see how to make it work using Hamachi.
This tool creates a virtual network you can use to play with your friends, without opening any ports to the outside world.
The only downside is that the free version allows a maximum number of 5 people in a single network. You can however, create as many networks as you want.
Downloading and installing Hamachi
This is really simple, go to https://vpn.net and click the big green download now button (it's not an ad, I swear ;))
Follow the instructions in the installer, after which you will be greeted with the Hamachi window.
Registering for Hamachi
The first time you launch or power on Hamachi, you will have to create an account. Go ahead and do that now.
After powering on, you will see a virtual IP in the form of 25.x.x.x. Now you are able to join virtual networks.
You can create and join networks from the 'network' tab. Be sure to put a password, so random people can't join.
The Hamachi network adapter requires a low metric to function properly. To configure this:
Open start menu
Type ncpa.cpl and hit enter
Right click Hamachi adapter, then properties
Select Internet Protocol Version 4, then properties
At the bottom, make sure automatic metric is unticked
Set the metric to 1 and hit OK and close on all dialogs
On a standard Windows installation, your Windows Firewall will be switched on.
You can completely disable it for the Hamachi domain, which will allow people to join you as a host.
Search for "Windows Firewall" in the start menu
Click on Advanced Settings then Windows Defender Firewall Properties.
For the three profiles : Domain/Private/Public you can click "Customize" near Protected Network Connections
Hit OK and close on all dialogs
After Hamachi is powered on and you are in a network, you can host a game like you would normally on a LAN.
To join a game, you can right click any user in the Hamachi network to copy their IPv4 address. Connect like normally, or use a server browser if the game has one.
Hope this helps!