- Doom uses a peer to peer model with no central server.
- In the original DOS release IPX 4 player games and serial cable or modem 2 player games were supported out of the box.
- Later versions added the Death Manager! tool to make it easier to set up games.
- User made utilities allows for 4 player over serial or modem links, usage of a parallell cable, TCP/IP and NetBIOS.
Deathmatch is a multiplayer game style pioneered by Doom in which players face off against each other, their computers connected to each other.
- A point, called a frag, is granted to a player whenever they kill an opponent.
- Frags are deducted when a player commits suicide, or dies in a crusher or damaging floor.
- Upon death, players restart at a random deathmatch start.
- Players spawn with all keys, and keys are never placed on the map (there is currently no clean way to circumvent this).
- When the level ends, the intermission screen gives each player's frag count. (Note that many PWADs specialized for deathmatch play do not contain exits.)
- Due to bugs in the code, some players have more latency added to their movement than others. To compensate for this in duels it is customary to swap colors and play two games to negate the advantage.
A deathmatch game may use either normal or altdeath rules. In more recent times, classic deathmatch has become known as FFA (free-for-all), in order to differentiate it from other player-vs-player game modes.
Cooperative gameplay, often referred to as co-op or coop, is a multiplayer game mode in which human players cooperate against a given game's monsters. Cooperative play is the default game mode if deathmatch mode is not explicitly specified at the command line.
Because the players are not adversaries under coop rules, they are visible on one another's automaps, and each can even "look through the eyes" of his companions (perhaps inspired by Electronic Arts' 1993 tactical game Space Hulk), though their status bars cannot be viewed.
Some source ports allow for a variant of cooperative gameplay known as survival, in which each player has only a finite number of lives.
Vanilla Doom has support for up to four players in multiplayer games. The players are made distinct from each other by altering the suit color of each player. Player 1's suit is green, player 2's is indigo, player 3's brown and player 4's red. Many source ports increase the number of players supported and several ports also support custom player skins and skin colors.
Differences from single player mode
In vanilla Doom, certain game interface features behave differently in multiplayer mode. For example, any player can pause or unpause the game at any time, and using the "save" command causes the game to be saved in the same slot on each machine. Also, when accessing the in-game menus (options, sound, save, load, etc) the game does not pause.
During the design of a map, objects can be flagged to appear only in multiplayer games. In stock maps, this is normally used to insert extra weapons and powerups, which provide a more balanced supply of armaments in cooperative play and more interesting "arms races" during deathmatch play. Beginning with Doom II, some of the stock levels also contain extra monsters, usually boss monsters; these provide more fearsome opposition for cooperative play and act as booby traps in deathmatch play. (Because of the extra monsters, some speedrunners enjoy the challenge of completing max runs in multiplayer mode, using DOS utility programs to create a fake "second player" who neither moves nor attacks.) Some level designers use the multiplayer flag to block off shortcuts introduced for singleplayer compatibility, like the torches in Memento Mori's maps 14, 15 and 29.
VanillaDM is both a GUI launcher and a multiplayer utility made by Hypnotoad. It seeks to improve vanilla Doom multiplayer sessions when using the DOSBox MS-DOS emulator through a collection of tightly configured programs running underneath the VanillaDM GUI using IPX tunneling through TCP/IP.
Chocolate Doom is a source port which attempts to mimic almost all of vanilla Doom's original behaviour. This port remains highly compatible with Doom, and recent development versions are also compatible on a network level since it supports both TCP/IP and IPX.
Multiplayer-focused source ports
Players in search of co-op allies or deathmatch opponents should refer to this tutorial, which includes instructions on connecting to multiplayer servers and playing local splitscreen games.
ZDoom uses a TCP/IP architecture for all network play; the game state is tracked on a peer-to-peer system. Four further ZDoom-family ports have improved netplay by incorporating client-server network architecture:
- csDoom, based on ZDoom version 1.22, was the first client/server multiplayer port. Now deprecated by Odamex.
- Odamex, derived from csDoom 0.62 (with a new maintainer), aims to retain compatibility with vanilla Doom while providing client/server netplay.
- Zandronum, derived from Skulltag 0.98d, features compatibility with modern editing features such as DECORATE as well as several new gamemodes.
- ZDaemon, derived from csDoom by its ex-developer NightFang, originally used csDoom's ZDoom 1.22 version. It has since updated to ZDoom version 1.23 beta 33.
These ports are capable of running large-scale multiplayer games more smoothly, as they were written specifically with network play in mind. For multi-port use, Doom Explorer is recommended to see all available servers.
Multiplayer in Doom 3 is limited to deathmatch, with the exception of the Xbox Live port which supports two-player cooperative with modified maps. Although the BFG edition added six multiplayer-specific achievements, multiplayer was entirely removed in the 2019 re-release of the game.
The game features five dedicated deathmatch levels, as the campaign maps only support single-player.