Networking Internals

Architecture Overview

┌─────────────────────────────────────────────────────────────────────────┐
│                     Game Server Container                                │
├─────────────────────────────────────────────────────────────────────────┤
│  ┌─────────────────┐  ┌─────────────────┐  ┌────────────────────┐       │
│  │ LidgrenServer   │  │ GalaxyNetServer │  │ SteamGameServer    │       │
│  │ (Direct IP)     │  │ (GOG P2P)       │  │ NetServer (SDR)    │       │
│  └─────────────────┘  └─────────────────┘  └────────────────────┘       │
└─────────────────────────────────────────────────────────────────────────┘
                                   │
                                   │ HTTP (lobby creation)
                                   ▼
┌─────────────────────────────────────────────────────────────────────────┐
│                     Steam Auth Container                                 │
├─────────────────────────────────────────────────────────────────────────┤
│  Creates Steam lobbies via SteamKit2                                     │
│  Lobby metadata includes GameServer's Steam ID for client discovery      │
└─────────────────────────────────────────────────────────────────────────┘

Connections:
  Steam Client ──► Valve SDR Relay ──► Game Server
  GOG Client ──► Galaxy P2P ──► Game Server
  Any Client ──► Direct IP (UDP 24642) ──► Game Server

Connection Methods

Steam SDR (Steam Datagram Relay)

Steam clients connect through Valve's relay network:

1. Server logs in anonymously to Steam's GameServer API
2. Valve assigns the server a Steam ID
3. Steam-auth service creates a lobby with this ID
4. Players join the lobby and connect via Valve's relay

Benefits:

• No port forwarding required
• NAT traversal handled automatically
• ~99% connection success rate

GOG Galaxy P2P

GOG clients connect using Galaxy's P2P networking:

• Invite codes prefixed with "G"
• Works through most NATs without port forwarding
• Lower success rate (~50%) than Steam SDR

Direct IP (Lidgren)

Direct IP connections for specific use cases:

• Disabled by default
• Requires port forwarding (UDP 24642)
• No user ID tracking (farmhand ownership issues)

Key Implementation Files

File	Purpose
SteamGameServerService.cs	GameServer API and SDR initialization
SteamGameServerNetServer.cs	Steam client connection handling
GalaxyNetServer.cs	GOG client connection handling
steam-service/Program.cs	Lobby management HTTP endpoints

Steamworks API Usage

The server uses GameServer mode, not Client mode:

Feature	Client Mode	GameServer Mode
Init	SteamAPI.Init()	GameServer.Init()
Callbacks	SteamAPI.RunCallbacks()	GameServer.RunCallbacks()
Networking	SteamNetworkingSockets	SteamGameServerNetworkingSockets
Matchmaking	SteamMatchmaking	Not available (via steam-auth)

Lobby Creation

Steam lobbies require an authenticated Steam client. Since the GameServer API runs headless, the steam-auth container creates lobbies:

1. Steam-auth logs in with user credentials
2. Creates lobby via SteamMatchmaking
3. Sets lobby metadata with server's Steam ID
4. Clients discover server through lobby system

Ports

Port	Protocol	Purpose
24642	UDP	Steam SDR game port
27015	UDP	Steam SDR query port
5800	TCP	VNC web interface
8080	TCP	HTTP REST API
3001	TCP	Steam auth internal API

NAT Traversal

Steam SDR

Traffic routes through Valve's global relay network, handling NAT automatically.

GOG Galaxy

Uses STUN/TURN-like mechanisms for P2P connections. Less reliable than Steam SDR.

Direct IP

Requires port forwarding or open NAT (Full Cone).

Diagnosing Connection Issues

The netdebug tool provides network diagnostics:

docker compose exec server netdebug nat    # Check NAT type
docker compose exec server netdebug ping   # Test GOG server latency
docker compose exec server netdebug speed  # Test bandwidth

References

• Steam Datagram Relay
• ISteamNetworkingSockets
• Steamworks.NET