Unlike single-player, multiplayer games present a diverse set of environments.
Some of these approaches don't scale well or restrict performance.

Types of games:
1.Fully instanced world for limited number of players(Diablo2).
Players select a game instance/map to enter.
Each game is a new instance of the world. Multiple servers for multiple games.

2.Open world shared, instanced dungeons for parties(typical MMO).
Each server usually has a capacity for thousands of players and hosts the entire map.
Players have to choose server before login, but only one account is needed.

3.Decentralized Open World:different servers are responsible for each region(Second Life).
Each server hosts only a specific region or instance. Players travelling from server1-zone1 to server2-zone2 expirienced loading delays.

4.Sharded Open World: multiple servers host each copy of the world and are assigned duties dependent on load.Typically all servers are connected within one building and communicate extensively to sync content. This design is present in some MMOs hosted in cloud/datacenters.

5.Peer2peer multiplayer: most complex of multiplayer, where each player loads a copy of the world and others player clients have to sync world state. Allows true decentralization and unlimited scalability(provided bandwidth is sufficient: most ISPs limit upload bandwidth)

6.Player-Hosted multiplayer:one player acts as server(Diablo1). Common with single-player games with "multiplayer mode" over the internet.

7.LAN multiplayer: a local game mode where player are using low-latency connection to each other. Can be #6 or #5. Provides best gaming experience due low overhead of connections.

8.Proximity multiplayer(various mobile games): players are communicating with nearby players in wireless range. Augmented reality games use this method to enhance immersion.

9.Proxied World Servers: Players choose a world server, but are connected to it through proxy servers(a dedicated game server proxy) routing their packers inside same building(datacenter). The actual world server expiriences less latency because its communicates with nearby servers and not players themselves(reducing load).

10. Independent World Servers: similar to #2 except each world has its own login and account.
Players choosing a server, have to create an account for each server they want to play in.
Used for quick scaling and low-population servers(less than a thousand players).
Each game world is isolated entirely on one server.

11.Zone servers:similar to #3 and #4 with each zone in a region having its own server, used for concentrated PvP or player cities(this allows tiny areas to be served by dedicated servers, with empty zones handles by regional server). Each zone server syncs with region server which all sync with world server(the one player choose at login).