Hosting Over The Internet

On a home network, players join by typing your local address and it simply works. Over the internet you have to let traffic in, and the whole job is four ports and a firewall.

The ports

Both 1864 and 1865 are required. This is the mistake worth avoiding: forwarding only 1864 gets players a console page that loads, looks right, and never comes alive, because the page arrived over 1864 and the game connection it then tries to open on 1865 is blocked. A console that loads but stays in its waiting state is almost always this.

Forwarding the whole range 1864–1867 is simplest and costs you nothing.

1. Forward the ports on your router

Every router's interface differs, but the setting is called Port Forwarding, sometimes under a "virtual servers" or "NAT" heading. Add one entry:

• External port range: 1864–1867
• Internal port range: 1864–1867
• Protocol: TCP
• Internal address: the local IP of the machine running Horizons

The server prints its local address when it starts — that is the one to use. Give that machine a static or reserved address in your router's DHCP settings while you are in there; otherwise it will get a different one eventually and the forward will quietly point at nothing.

2. Let the host machine's own firewall through

The router forward gets traffic to the machine. The machine's firewall still has to accept it. On Windows, allow Horizons through Windows Defender Firewall on both private and public networks, or add inbound TCP rules for 1864–1867.

Third‑party security software is the usual culprit when the router is right and it still does not work — some suites silently block unrecognised listening programs. Check any antivirus or "network protection" feature separately from the Windows firewall.

3. Find your public address

Your local address means nothing to someone outside your network. Visit whatismyip.com and note the IPv4 address it reports.

Most home connections change this address from time to time, so check it again before each session rather than reusing last week's link. If you host often, a dynamic DNS name saves you the trouble.

4. Share the link

http://203.0.113.45:1864/

The :1864 is not optional — without it the browser tries port 80 and gets nothing. Players see the same station selection page as everyone else.

Checking it from outside

Testing your public address from inside your own network is unreliable: many routers will not route a connection back to themselves, so it can fail while working perfectly for everyone else. Ask someone outside your network to try it, or use a phone on mobile data with Wi‑Fi turned off.

Things that catch people out

• Two routers. A router behind an ISP modem‑router means two sets of forwards. Forward on both, or put one in bridge mode.
• Carrier‑grade NAT. Some ISPs, especially mobile and some fibre providers, do not give you a real public address at all — port forwarding cannot work and no amount of configuration will change it. If your router's WAN address is in the 100.64–100.127 range, this is your situation. A VPN between players, or hosting elsewhere, is the way round it.
• Upstream bandwidth. Consoles are lightweight, but the host is serving every one of them. A weak upload will show as consoles lagging behind the simulation rather than as a failure to connect.
• Handing out an admin station. Anyone who reaches your server can choose any visible station, including Game Master. Over the internet, that is a stranger with your session controls. There is no per‑station password: treat the link as the credential and only share it with your players.