A Nitrox server is what turns Subnautica, a single-player game, into multiplayer, and “unable to connect to remote server” (the exact message reads “Unable to contact the remote server at:”) is what you see when friends can’t reach it. Nitrox is a free, open-source fan mod, not an official Unknown Worlds feature. The host runs the Nitrox server, everyone installs the same Nitrox version, and players connect on UDP port 11000. This guide covers setup, settings and commands, then every reason that connection fails.
What Nitrox is (and isn’t)
Nitrox is an unofficial multiplayer mod for the original Subnautica, built by volunteers and released under the GPLv3 license. It is still described by its own team as in development, so expect bugs. The latest release is 1.8.1.0 (January 2026), which works with the Steam, Epic Games and Microsoft Store versions of the game; the Microsoft Store version needs extra setup, explained on the Nitrox Discord. Nitrox runs on Windows and Linux.
Is Nitrox free and safe? It’s free: the team doesn’t even take donations. The source code is public on GitHub, and the official download is on nitrox.rux.gg. Get it there, not from a re-upload.
Subnautica 2 is different. It came out in Early Access on 14 May 2026 with its own online co-op for up to four players (you and three friends), so it doesn’t need Nitrox. Everything below is about the original Subnautica.
Requirements for hosting a Nitrox server
- The game: every player needs their own copy of Subnautica and the same Nitrox version as the server. Nitrox refuses mismatched versions.
- RAM: 4–8 GB for the server. Nitrox tracks world state the base game never had to save (every player’s position, vehicles, bases), so it is heavier than people expect.
- Network: UDP port 11000 open to the internet, or a VPN tool like Hamachi that puts everyone on one virtual network.
- Players: the Nitrox team lists a maximum of 100, but recommends 5. It’s built for a group playing through the story together.
How to install Nitrox
- Download Nitrox from nitrox.rux.gg.
- Unzip it to a folder of its own. Don’t run it from inside the zip: it won’t save its progress and gets buggier.
- Run NitroxLauncher as Administrator.
- Open Options, click Change and point it at your Subnautica folder, for example
C:\Program Files\Steam\steamapps\common\SubnauticaorC:\Program Files\Epic Games\Subnautica.
Everyone who plays does this, host included.
How to host a Nitrox Subnautica server
The host starts the server from the Nitrox Launcher, opens UDP port 11000 (or lets Nitrox open it automatically through UPnP), and gives friends their public IP. Unlike a Minecraft server, there’s no separate server download: the server ships inside Nitrox, as NitroxServer-Subnautica.exe. The steps:
- Run NitroxLauncher as Administrator.
- Click Server, create or pick a world, then Start Server.
- Read the server window. It shows the game mode, the server password, the admin password, your local IP (for LAN play or joining yourself) and the IP others need if you port forward.
- Make sure UDP 11000 reaches the host. Nitrox tries UPnP first (
AutoPortForwardis on by default), but many routers have it switched off, so forward it by hand if friends can’t connect. - Allow
Subnautica.exeandNitroxServer-Subnautica.exethrough the firewall, on the host and on each player’s PC.
Want a true dedicated server, one that stays up when the host logs off? Run the Nitrox server on a machine that stays on, or rent one with Subnautica: Nitrox server hosting. Your friends can keep building at night while you sleep.
How to join a Nitrox server
- Open the Nitrox Launcher (as Administrator) and press Multiplayer.
- Press Add server IP, give the server a name and type the host’s IP under Host. Add
:portonly if the host changed it from 11000. - Click Connect to…, pick a username and a color, and press Join.
On the same network as the host, use the host’s local IP; Nitrox also answers LAN discovery requests by default. Outside it, use the public IP from the server window.
Fix “unable to contact the remote server” in Nitrox
“Unable to contact the remote server at:” means your game sent a request to that address and got no answer. Either the address is wrong, the server isn’t running, or something between you blocks UDP 11000. A version mismatch shows a different message (“Your Nitrox installation is out of date” or “The server runs an older version of Nitrox”). Work through the checks in order:
- Is the server actually running? The server window should be open and finished loading. A big world can take a while on first start.
- Right IP? Friends outside your home need your public IP. Players on your network need the local one. The server window shows both.
- Port 11000 UDP open? Forward UDP (not just TCP) 11000 on the host’s router to the host PC. If UPnP failed, Nitrox says so in the server log.
- Firewall exceptions? Both
Subnautica.exeandNitroxServer-Subnautica.exe, on both ends. Antivirus suites with their own firewall count too. - Behind CGNAT? Some ISPs share one public IP across many homes, and then no port forward will ever work. If the IP on your router’s WAN page differs from the one “what is my IP” shows, that’s you. Use a VPN tool like Hamachi, or host somewhere with a real public IP.
- Did Subnautica just update? A game patch can break Nitrox until a matching Nitrox build comes out, and that presents as being unable to connect. Check the Nitrox Discord before you take your router apart.
- IPv6: Nitrox 1.8.1.0 added IPv6 support. If you’re on an older build, everyone should update.
| What you see | Cause | Fix |
|---|---|---|
| “Unable to contact the remote server at: …” | No answer from that IP and port | The checklist above: server running, IP, UDP 11000, firewall, CGNAT |
| “Your Nitrox installation is out of date” | Your Nitrox is older than the server’s | Update to the server’s version |
| “The server runs an older version of Nitrox” | The host is behind | Host updates the server, or you downgrade |
| “Server password required” | ServerPassword is set |
Ask the host for it |
| Can’t connect right after a game patch | Subnautica changed, Nitrox hasn’t caught up | Wait for a Nitrox update |
Nitrox server settings (server.cfg)
Each world has its own folder under %AppData%\Nitrox\saves\, with a server.cfg inside. The launcher’s server settings screen edits the same file. Stop the server before changing it by hand. The settings that matter:
| Key | Default | What it does |
|---|---|---|
ServerPort |
11000 | The UDP port players connect to |
ServerPassword |
empty | Password to join; empty means open |
AdminPassword |
random, 12 characters | Used with /login to become admin |
GameMode |
SURVIVAL | The world’s game mode |
Seed |
random | World seed; leave blank for a random spawn position |
KeepInventoryOnDeath |
false | Players keep their items when they die |
PvPEnabled |
true | Player-versus-player damage |
MaxConnections |
100 | Player cap |
SaveInterval |
120000 | Autosave every 2 minutes (in milliseconds) |
MaxBackups |
10 | How many automatic backups to keep |
AutoPortForward |
true | Try to open the port through UPnP |
LANDiscoveryEnabled |
true | Answer LAN discovery so local players find the server |
LocalhostIsAdmin |
true | Players on the host’s own machine get admin automatically |
DefaultPlayerPerm |
PLAYER | Permission level for new players |
The save folder is also your backup: copy the whole world folder while the server is stopped and you have everything, server.cfg included. To reset a Subnautica server, stop it and start a new world rather than deleting files from a live one. The server’s --data-path argument moves all of Nitrox’s files (saves, logs, cache) somewhere else.
Nitrox server commands
Type commands in the server console, or in game chat with a / in front. In game you need the right permission level, so log in first with /login <AdminPassword>.
| Command | Permission | What it does |
|---|---|---|
help |
Player | Lists the commands you can use |
list |
Player | Shows who’s online |
login <password> |
Player (in game only) | Logs you in as admin |
whisper, whois |
Player | Private message; player info |
save |
Moderator | Saves the world now |
kick, mute / unmute |
Moderator | Remove or silence a player |
broadcast |
Moderator | Message everyone |
time |
Moderator | Changes the time of day |
teleport, warp, back |
Moderator | Move yourself or other players |
promote |
Moderator | Sets a player’s permission level |
op / deop |
Admin | Gives or removes admin |
backup, autosave |
Admin | Makes a backup; toggles autosave |
pvp, keepinventory |
Admin | Toggles PvP; keep items on death |
changeserverpassword, changeadminpassword |
Admin | Changes the passwords |
changeservergamemode, gamemode |
Admin | World or per-player game mode |
aurora, sunbeam |
Admin (in game only) | Control story events |
stop |
Admin | Stops the server |
Finding Nitrox servers and the community
In the launcher you add servers by IP, so you need the address from the host. To find other players or public Nitrox servers, use the official Nitrox Discord (linked from nitrox.rux.gg) or the r/SubnauticaNitrox Reddit community. The Nitrox team doesn’t run those public servers and doesn’t moderate them. The Discord is also where bugs and new versions get discussed first.
Skip the setup: rent a Nitrox server
A home-hosted Nitrox world closes when the host’s PC sleeps, and UDP forwarding, UPnP and CGNAT cause most “unable to contact the remote server” evenings. Subnautica: Nitrox server hosting on GameTeam runs the server around the clock with a real public IP, so friends paste one address and dive in. You pay per GB of RAM ($0.49/GB a week on Budget, or $1.99/GB billed monthly), so a 4 GB world is $1.96 a week. The built-in AI copilot keeps the server’s Nitrox version straight and tells you when a Subnautica update has broken it. Tell it “turn on keep inventory, set a server password and back up the world” and it edits server.cfg, restarts the server and confirms the change. When the ocean is explored, the same server can switch to another game, like Minecraft or Valheim.
FAQ
Is there any way to play Subnautica multiplayer?
Only through the Nitrox mod. Subnautica itself is single-player, and Nitrox adds the server, the syncing and the chat. Subnautica 2 has its own built-in co-op.
Is Nitrox for Subnautica free?
Yes. Nitrox is free and open source, and its team doesn’t accept money. Each player still needs to own Subnautica.
Is Nitrox safe?
The official build comes from nitrox.rux.gg and its source code is public on GitHub. It’s an unofficial mod in development, so back up your saves, and expect the occasional desync or bug.
How do I start a Subnautica server?
Install Nitrox, run the Nitrox Launcher as Administrator, click Server, then Start Server. Share the IP from the server window and open UDP 11000.
Why can’t I connect to the Nitrox server?
Usually UDP 11000 isn’t reaching the host (no port forward, UPnP off, a firewall, or CGNAT), the IP is wrong, or a recent game update broke Nitrox. The full checklist is above.
What port does a Subnautica Nitrox server use?
UDP 11000 by default. Change it with ServerPort in server.cfg and have players add :port after the IP.
Is there a Subnautica dedicated server without Nitrox?
No. The original game has no server software of its own. A “Subnautica dedicated server” is a Nitrox server running on a machine that stays online.