Multiplayer Networking

Authoritative servers, client prediction, and state synchronization define robust multiplayer.

net_enet_expert_config.gd

Expert logic for tuning ENet channels, compression, and bandwidth thresholds.

net_packet_bit_packer.gd

Professional manual serialization tools for bit-packing data into PackedByteArray.

net_headless_server_auto_start.gd

Logic for detecting dedicated server mode and parsing CLI arguments for headless launch.

net_heartbeat_monitor.gd

RTT (Round Trip Time) and Jitter monitoring system for high-fidelity lag tracking.

net_lan_discovery.gd

UDP broadcasting system for local server discovery without master servers.

net_adaptive_sync_throttle.gd

Dynamic synchronization manager that adapts sync-rates to peer connection quality.

net_anti_desync_reconciler.gd

Server-authoritative state validation and forced-correction logic.

net_visibility_grid_culling.gd

Interest Management system for optimizing bandwidth in large-scale worlds.

net_packet_rate_limiter.gd

Essential flood-protection and anti-spam manager for RPC security.

net_custom_id_mapper.gd

Mapping utility for linking permanent UserIDs to volatile Network PeerIDs.

NEVER Do (Expert Networking Rules)

Core Architecture

NEVER use Reliable for high-frequency data (Position/Movement) — Reliable packets block all following packets until acknowledged (Head-of-Line blocking). Use UnreliableOrdered.
NEVER trust the client for shared state (Health/Money/Inventory) — Clients should only suggest actions. The Server MUST validate and broadcast the result.
NEVER hardcode the Server IP — Always allow for discovery (net_lan_discovery.gd) or pass the IP via CLI/UI.

Performance & Bandwidth

NEVER send the same data every frame — Use net_adaptive_sync_throttle.gd to only send updates when state changes significantly or at fixed Hz intervals (e.g., 20Hz).
NEVER use JSON for high-speed synchronization — String serialization is massive over the wire. Use bit-packing (net_packet_bit_packer.gd) to keep packets under 100 bytes.
NEVER broadcast to all peers if it's not needed — In large worlds, use Interest Management (net_visibility_grid_culling.gd). A player in the forest doesn't need the position of a player in the city.

Security

NEVER allow unlimited RPC calls per second — An attacker can flood the server with 1,000 "Attack" RPCs to crash the game. Use net_packet_rate_limiter.gd.
NEVER expose PeerIDs to the end-user — PeerIDs are internal. Always map them to persistent UserIDs (net_custom_id_mapper.gd) from a database.
NEVER run a dedicated server with a GUI enabled — Use --headless (net_headless_server_auto_start.gd) to save resources and ensure stability.

Authoritative Server Model:

Server validates all game state
Clients send inputs, receive state
Prevents cheating

Peer-to-Peer:

Direct player connections
Good for small player counts
No dedicated server needed

Basic Setup

Create Multiplayer Peer

extends Node

var peer := ENetMultiplayerPeer.new()

func host_game(port: int = 7777) -> void:
    peer.create_server(port, 4)  # Max 4 players
    multiplayer.multiplayer_peer = peer
    print("Server started on port ", port)

func join_game(ip: String, port: int = 7777) -> void:
    peer.create_client(ip, port)
    multiplayer.multiplayer_peer = peer
    print("Connecting to ", ip)

Connection Signals

func _ready() -> void:
    multiplayer.peer_connected.connect(_on_peer_connected)
    multiplayer.peer_disconnected.connect(_on_peer_disconnected)
    multiplayer.connected_to_server.connect(_on_connected)
    multiplayer.connection_failed.connect(_on_connection_failed)

func _on_peer_connected(id: int) -> void:
    print("Player connected: ", id)

func _on_peer_disconnected(id: int) -> void:
    print("Player disconnected: ", id)

func _on_connected() -> void:
    print("Connected to server!")

func _on_connection_failed() -> void:
    print("Connection failed")

Remote Procedure Calls (RPCs)

Basic RPC

extends CharacterBody2D

# Called on all peers
@rpc("any_peer", "call_local")
func take_damage(amount: int) -> void:
    health -= amount
    if health <= 0:
        die()

# Usage: Call on specific peer
take_damage.rpc_id(1, 50)  # Call on server (ID 1)
take_damage.rpc(50)  # Call on all peers

RPC Modes

# Only server can call, runs on all clients
@rpc("authority", "call_remote")
func server_spawn_enemy(pos: Vector2) -> void:
    pass

# Any peer can call, runs locally too
@rpc("any_peer", "call_local")
func player_chat(message: String) -> void:
    pass

# Reliable (TCP-like) vs Unreliable (UDP-like)
@rpc("any_peer", "call_local", "reliable")
func important_event() -> void:
    pass

@rpc("any_peer", "call_local", "unreliable")
func position_update(pos: Vector2) -> void:
    pass

MultiplayerSpawner

# Add MultiplayerSpawner node
# Set spawn path and scenes

extends Node

@onready var spawner := $MultiplayerSpawner

func _ready() -> void:
    spawner.spawn_function = spawn_player

func spawn_player(data: Variant) -> Node:
    var player := preload("res://player.tscn").instantiate()
    player.name = str(data)  # Use peer ID as name
    return player

MultiplayerSynchronizer

# Add to synchronized node
# Set properties to sync

# Scene structure:
# Player (CharacterBody2D)
#   ├─ MultiplayerSynchronizer
#   │    └─ Replication config:
#   │         - position (sync)
#   │         - velocity (sync)
#   │         - health (sync)
#   └─ Sprite2D

Lobby System

# lobby_manager.gd (AutoLoad)
extends Node

signal player_joined(id: int, info: Dictionary)
signal player_left(id: int)

var players: Dictionary = {}

func _ready() -> void:
    multiplayer.peer_connected.connect(_on_peer_connected)
    multiplayer.peer_disconnected.connect(_on_peer_disconnected)

func _on_peer_connected(id: int) -> void:
    # Request player info
    request_player_info.rpc_id(id)

func _on_peer_disconnected(id: int) -> void:
    players.erase(id)
    player_left.emit(id)

@rpc("any_peer", "reliable")
func request_player_info() -> void:
    var sender_id := multiplayer.get_remote_sender_id()
    receive_player_info.rpc_id(sender_id, {
        "name": PlayerSettings.player_name,
        "color": PlayerSettings.player_color
    })

@rpc("any_peer", "reliable")
func receive_player_info(info: Dictionary) -> void:
    var sender_id := multiplayer.get_remote_sender_id()
    players[sender_id] = info
    player_joined.emit(sender_id, info)

State Synchronization

extends CharacterBody2D

var puppet_position: Vector2
var puppet_velocity: Vector2

func _physics_process(delta: float) -> void:
    if is_multiplayer_authority():
        # Local player: process input
        _handle_input(delta)
        move_and_slide()
        
        # Send position to others
        sync_position.rpc(global_position, velocity)
    else:
        # Remote player: interpolate
        global_position = global_position.lerp(puppet_position, 10.0 * delta)

@rpc("any_peer", "unreliable")
func sync_position(pos: Vector2, vel: Vector2) -> void:
    puppet_position = pos
    puppet_velocity = vel

Authority

# Check who owns this node
func _ready() -> void:
    # Set authority to owner peer
    set_multiplayer_authority(peer_id)

func _process(delta: float) -> void:
    if not is_multiplayer_authority():
        return  # Skip if not owner
    
    # Only authority processes this

Best Practices

1. Validate on Server

@rpc("any_peer", "call_local")
func player_action(action: String) -> void:
    if not multiplayer.is_server():
        return  # Only server validates
    
    var sender := multiplayer.get_remote_sender_id()
    if not _is_valid_action(sender, action):
        return
    
    _apply_action.rpc(sender, action)

2. Use Unreliable for Frequent Updates

# Position: unreliable (frequent)
@rpc("any_peer", "unreliable")
func sync_position(pos: Vector2) -> void:
    pass

# Damage: reliable (important)
@rpc("authority", "reliable")
func apply_damage(amount: int) -> void:
    pass

3. Interpolation for Smooth Movement

var target_position: Vector2

func _process(delta: float) -> void:
    if not is_multiplayer_authority():
        position = position.lerp(target_position, 15.0 * delta)

Reference

Godot Docs: High-level Multiplayer

Master Skill: godot-master

godot-multiplayer-networking