Multiplayer refers to games against other humans, in contrast to single player. It is still possible to add AI opponents if desired.
One player is the host of the game and others join. The methods of hosting are below. It should be noted that the host's computer manages AI and projectiles, so the person with the fastest CPU should always host in arranged matches, unless their connection speed is inadequate.
It is possible to host a game in Supreme Commander and Supreme Commander: Forged Alliance if you know the IP address of the host. If the host is on the LAN (houshold, office, internet café) you can find it within the game.
Finding a person hosting can be managed by the GPGNet program included with Supreme Commander and FA. Games managed by GPGNet include custom and ranked games. Ranked games affect a player's rating, to help match players of relatively equal skill. It should be noted that Gas Powered Games published an official multiplayer FAQ. GPG net is currently offline.
The Steam version of Supreme Commander Vanilla and FA use a seperate Steam hosting system. A helpful tip for those who still have their Supreme Commander keys is that if you use them to obtain the game on Steam it will work.
(fyi i am edting this )steam does not have supreme commander any more.
Due to GPG net's state of decay and possible future shutdown members of the Supreme Commander community put together Forged Alliance Forever (FAF). The goal of this multiplayer server is to allow Supreme Commander: Forged Alliance games to be played even if GPG Net is shut down. FAF's website is www.faforever.com.
Forged Alliance Forever offers a multiplayer ladder, competitive tournaments, a map vault, a replay vault and integrated mods. Those mods include: LAB wars, Blackops, FAF (the basic game which has some bug fixes and Sorian AI), Murder Party, Nuke For The Win, Wyvern Battlepack, and X'treme Wars.