Letting players reach your machine

If your machine is at home, your friends on the same Wi-Fi can join straight away. Players outside your home can only join if your router lets them in. That's called port forwarding.

In Warp View, every machine has a Can players reach this machine? button. It tries your machine from the internet, the way a player would, and tells you which ports are open.

Friends can't join? Quick checks

1. Is the server running in Warp View, and are your friends using the join address shown on the server's page?
2. Press Can players reach this machine? on the machine. Anything marked Not reachable needs a port forward (below).
3. If every forward is in place and it still says Not reachable, you may be behind CGNAT (see the end of this guide).
4. Can't make it work at home? A cloud server in your own account needs no port forwarding.

What port forwarding is

Your router has one address on the internet, shared by everything in your home. When a player connects, the router has to know which device to send them to. A port forward is a rule on the router: "traffic for port 2456 goes to the computer at 192.168.1.50".

You add one rule for each port a server uses.

Which ports to forward

Each server's ports are listed on its card in Warp View. A new server normally gets these (TCP+UDP means forward both):

If you run more than one server of the same game, or the usual ports were taken, a server gets ports between 30000 and 30199 instead. Always check the server's card.

Don't forward admin ports. Palworld's and ARK's RCON port and 7 Days to Die's Telnet port are for managing the server, not for players. Leave them closed to the internet. The reachability check doesn't test them.

Cosmic Warp itself also needs TCP 8080. Port 8080 lets Cosmic Warp's control panel talk to your machine securely: it's how Warp View starts, stops and swaps your servers (the program listening there is called Wings, and the connection is encrypted). Players never use it. Forward it too, unless you use tunnel mode (below).

Tunnel mode (Linux machines): if you'd rather not open 8080, install with Cloudflare Tunnel mode instead. You need a free Cloudflare account and a domain on it. In Cloudflare, create a tunnel, copy its token, and give it a public hostname (for example node1.example.com) that points to https://localhost:8080. Then add --tunnel <tunnel token> --tunnel-hostname node1.example.com to the end of the install command from Warp View (the install-node.sh line). The installer sets up Cloudflare's cloudflared and doesn't open 8080 on the machine. Tunnel mode is new and not yet tested on many machines, and the Windows 11 installer doesn't offer it yet. It only covers Cosmic Warp's connection: your game ports still need forwarding for players.

How to add the forwards

1. Find your machine's local address. On the machine: Linux hostname -I (the first address); Windows, Settings, Network, your connection, "IPv4 address". It usually looks like 192.168.x.x or 10.x.x.x.
2. Give it a fixed address. In the router, look for "DHCP reservation", "static lease" or "address reservation", and reserve that address for the machine. Otherwise the forward can point at the wrong device after a restart.
3. Open the router's settings page. Type your router's address into a browser: usually 192.168.1.1, 192.168.0.1 or 10.0.0.1 (often printed on a sticker on the router). Some providers use an app instead (Xfinity, Eero, Google/Nest Wifi).
4. Find port forwarding. It may be called "Port Forwarding", "Virtual Server", "NAT" or "Applications and Gaming", often under Advanced.
5. Add one rule per port: the port number (same outside and inside), the protocol (TCP, UDP or both) and the machine's local address.
6. Check it. Back in Warp View, press Can players reach this machine?.

UPnP: opened automatically

Many routers have UPnP, which lets programs open ports by themselves. Machines connected with Cosmic Warp Setup or the Linux installer try it: while a server runs, its ports are opened on your router, and closed when it stops. Your machine's card in Warp View then says Opened automatically. If your router has UPnP turned off (or doesn't have it), nothing happens and the card says Direct: add the forwards by hand as above. Forwards you add by hand keep working either way.

When forwarding can't work: CGNAT

Some internet providers (common with fixed wireless, 5G home internet, some fiber and cable plans, and many mobile hotspots) share one public address between many homes. This is called CGNAT. With CGNAT, nothing you set on your router lets players in, because the address the internet sees isn't your router's.

How to tell:

• The reachability check says your machine reported a CGNAT address (100.64.x.x to 100.127.x.x), or that its address doesn't match where its heartbeats come from.
• Or check yourself: compare the "WAN" or "Internet" address on your router's status page with what a site like whatismyip.com shows. If they're different, you're behind CGNAT (or a second router).

What to do:

• Use the Cosmic Warp relay (paid plans; Starlink included). Tick Starlink, 5G home internet, or can't forward ports? in Connect a machine before generating the command (Linux and Windows). The machine keeps an outgoing, encrypted tunnel to our relay; players join at the relay's address that Warp View shows, and nothing has to be opened on your router. The relay passes only your servers' own ports, and game servers see players as coming from the relay (so per-player IP bans don't work through it). Each plan includes a monthly amount of relay traffic: Pilot 100 GB, Commander 300 GB, Host 1 TB; past that it slows down rather than stopping. An already-connected machine moves to the relay by removing it in Warp View and connecting it again with the relay ticked.
• Ask your provider for a public IPv4 address. Many will turn it on for free or a small monthly fee.
• Use tunnel mode when installing a Linux machine (--tunnel, see above), so Cosmic Warp's control panel reaches the machine without port 8080 being open. Players still need a way in for the game itself, so this helps with managing the machine, not with players joining. It's new and not yet tested on many machines.
• Run the server somewhere else: a cloud server from your own account (Launch a cloud server in Warp View).

Still stuck

• Two routers (for example your provider's modem-router plus your own Wi-Fi router): forward on the first one to the second, and on the second to the machine. Or put the provider's box in "bridge mode".
• A firewall on the machine: Cosmic Warp's installer opens the ports in Ubuntu's firewall (and, on Windows 11, in Windows Firewall).
• The check says "Unknown" for UDP: some games can't be tested automatically. Ask a friend outside your home to try joining.