Even though Mplayer, Heat.net, and Gamespy are shut down, you can still connect to other people. The 3 basic steps to get multiplayer to work is to unblock the game from your firewall, forward three ports, and enable DirectPlay.

Firstly, make sure your firewall isn't blocking the game (it will usually ask you after you close the game). The program should say "wheels.exe" as the file name.

If you're wanting to play online and not locally, you will need to forward the following ports on your router:
TCP/UDP 2300
TCP/UDP 47624
UDP 6073
If you need help on how to forward ports, check out our Troubleshooting page.

Finally, you will need to enable DirectPlay. A lot of games relied on this to play online, but was disabled after Windows 7. Goto your Control Panel (Windows settings), click on Programs and Features, click on Turn Windows Features On/Off at the left hand side, click the + next to Legacy Components, tick the box next to DirectPlay to enable it, click OK. Sometimes, Windows will automatically ask you to enable this feature when trying to play an old game, but it seems to be random.

To join an internet-based game, you will need to go to Multiplayer at the main menu, click on Internet (TCP), click Join, enter the host's IP address, then click on the Internet button above. The game will now search for the host and should connect, assuming everyone has forwarded the necessary ports and unblocked it from the firewall.

If you wish to play LAN on Windows 10, along with the same steps above at the beginning, all of the PCs must be on the same home network (such as using the same wifi). In the usual multiplayer menu, simply use the Internet button, but leave the IP address box blank. It will search for games on the same network, and it should show up.

If you want to play LAN but don't have internet, and only have ethernet cords to connect, you must download and install IPXWrapper. Versions after Windows Vista no longer supports the IPX interface and so a wrapper must be used. Extract the files of the ZIP into its own folder, copy the 4 DLL files (dpwsockx, ipxwrapper, mswsock, wsock32), paste them into your main Redline folder, go back to the other folder and double click the directplay-win64 file (unless you're running a 32-bit Windows, which in that case use directplay-win32), and click OK to add to the registry. The LAN option in the Multiplayer menu should now appear and you can use an ethernet cable to connect the PCs.

There's also an old program called Kali that exists since 1995, and supports Redline as well. Although as of this writing, it has not been properly tested.

To host a multiplayer game, be sure to do all the steps at the beginning of this page up above. Then, you will need to give your IP to everyone who intends to join. The best way to figure out your IP address is to type what is my ip in to Google. By hosting a game, you are able to change various options, such as:

Note that 3 of the maps are strictly for Capture the Flag mode.
If someone selects the same gang, the score is counted as a team. This can be turned on or off.
This can be turned on or off, which means if someone is on the same team, they cannot hurt each other.
The map will end once a certain score or time is reached.
The amount of players that is allowed in the server, 12 is the max.
If this is enabled, that means for the 3 specific CTF maps, a point cannot be gained from a captured flag unless your team's flag is still at your base. If this is disabled, that means a point can be gained from a captured flag, regardless if your team's flag is in possession of the enemy, or not.
This will enable everyone's weapon crosshair to turn red if hovered over something that can be destroyed, such as another vehicle or player.
Obviously, this sets the name of your server.
If you want to run a dedicated server (which is a condensed version of Redline, a small window that can be ran in the background), create a shortcut of your redline.exe file (right click it and then click Create shortcut), then right-click the new shortcut, goto Properties, click the Shortcut tab, and in the Target box after it says \redline.exe", type in +console and click OK.