FS2004 online multiplayer still works by direct IP. Learn the DirectPlay ports, public IPv4 and NAT setup, plus the supported VATSIM client.
Yes. Microsoft Flight Simulator 2004 (FS2004/FS9) private multiplayer still works through DirectPlay and TCP/IP when the host has a reachable public IPv4 address and the required ports are open. Microsoft’s old public lobby is gone, and FS2004 sessions are not compatible with FSX, Microsoft Flight Simulator 2020 or Microsoft Flight Simulator 2024.
What parts of FS2004 multiplayer still work?
The Microsoft public lobby does not work, but direct-IP, LAN and privately networked sessions do. FS2004 does not need a central Microsoft server when one player hosts and the others connect directly.
| Connection method | Use it when | Main requirement |
|---|---|---|
| LAN | Everyone is connected to the same home or club network | Players join using the host’s LAN IPv4 address |
| Direct internet connection | A known group wants a private flight | The host needs reachable public IPv4, firewall permission and router forwarding |
| Trusted private virtual network | The host is behind difficult NAT or participants want a private virtual LAN | Every participant must join the same trusted network and use its assigned IPv4 address |
| Organised flying network | Pilots want shared traffic and structured air traffic control | A supported pilot client is used instead of FS2004’s built-in session |
FS2004 direct multiplayer synchronises player aircraft, not the whole simulator state. It is not a native shared-cockpit system, and local AI traffic, ATC, weather and add-on behaviour may differ between computers.
How do I host and join an FS2004 multiplayer session?
Set up the host’s addresses and network rules before creating a password-protected TCP/IP session inside FS2004.
- Match the FS2004 installations. Everyone should run FS2004 at the same update level. If necessary, use our guide to installing the FS9.1 update and other FS2004 patches.
- Enable DirectPlay on modern Windows. Open Windows Features and enable
Legacy Components > DirectPlay. Windows may instead prompt to install it when FS2004 first accesses multiplayer. - Find the host’s LAN IPv4 address. On the host PC, run
ipconfigand read the IPv4 Address under the active Ethernet or Wi-Fi adapter. Do not use the Default Gateway or an address belonging to a disconnected virtual adapter. - Identify the internet-facing public IPv4 address. Check the Internet or WAN status on the outermost router. Remote players need this address, while players on the same LAN use the address found with
ipconfig. If the router shows a private or carrier-grade address, use the NAT diagnosis below. - Reserve the host’s LAN address. Create a DHCP reservation in the router so it always assigns the same LAN IPv4 address to the host PC. This prevents port forwarding from silently pointing to another device after a restart.
- Configure the host firewall and router. Permit
fs9.exeon the network profile being used, then forward the DirectPlay UDP ports to the reserved LAN address. LAN-only sessions do not need internet port forwarding. - Create the FS2004 session. Open FS2004’s multiplayer screen, choose its TCP/IP connection option, create the session and set a password. Share the password and address only with the intended pilots. Menu wording can vary slightly between installations.
- Join using the correct address. A LAN participant enters the host’s LAN IPv4 address. An internet participant enters the public IPv4 address. A private virtual-network participant uses the host’s address on that virtual network.
- Test with stock aircraft. Put two default aircraft at the same airport and confirm that both users can connect and see one another. Introduce add-on aircraft, weather tools and other utilities one at a time after the basic session works.
Our original direct-IP multiplayer walkthrough covers the in-simulator connection procedure. Groups wanting a persistent private hub can also examine the MP-Lite Server 2.1 package for FS2004 hosting, but a third-party server utility may use different ports from FS2004’s built-in session.
Which firewall and router ports does FS2004 multiplayer need?
FS2004’s built-in multiplayer uses DirectPlay 8, whose normal inbound port set is UDP 6073 and UDP 2302–2400.
| Purpose | Protocol | Port | Where it is required |
|---|---|---|---|
| DirectPlay connection and session discovery | UDP | 6073 | Host firewall and internet-facing router |
| DirectPlay session traffic | UDP | 2302–2400 | Host firewall and internet-facing router |
Although the FS2004 menu describes the connection as TCP/IP, the normal DirectPlay 8 traffic that needs forwarding is UDP. Older generic DirectPlay instructions often list TCP 47624 and TCP/UDP 2300–2400; those are DirectPlay 7-era values and should not be the starting rules for FS2004’s built-in DirectPlay 8 session.
Create the forwarding rules only after reserving the host PC’s LAN address, and direct every rule to that address. In Windows Firewall or a separate security suite, restrict permission to fs9.exe and the network profile in use where possible. A virtual network adapter may be classified as a Public network, so check its profile rather than enabling every profile indiscriminately.
Does every FS2004 player need port forwarding?
No. Port forwarding is normally required only on the router protecting the host; joining clients make outbound connections and usually need no inbound mapping.
Remove the router forwarding and any temporary firewall rules when the group has finished using them. Never disable the firewall or put the FS2004 computer in an unrestricted DMZ as a troubleshooting shortcut.
Why can nobody join the FS2004 session?
Most failed internet sessions come from using the wrong address, forwarding to an old LAN address, or trying to host behind NAT that cannot accept inbound IPv4 traffic.
| What the host sees | Likely cause | What to do |
|---|---|---|
Address begins 10., 192.168. or 172.16–172.31 | Private LAN address | Use it only for local players; remote players need the outermost router’s public IPv4 address |
| Personal router’s WAN address is private | Double NAT | Configure the upstream router as well, use bridge or passthrough mode if appropriate, or choose another hosting method |
WAN address is within 100.64.0.0–100.127.255.255 | Carrier-grade NAT | Ask the ISP for reachable public IPv4, let another player host, or use a trusted private virtual network |
| No usable WAN IPv4 address is assigned | IPv6-only service or provider translation | Request public IPv4 or use an IPv4-capable private virtual network |
| The session worked previously but stopped after a router reconnect | Dynamic public IPv4 changed | Check the public address again and send the new value privately to participants |
| LAN players cannot connect | Wrong adapter, firewall rule, guest Wi-Fi or client isolation | Use the host’s active LAN address and ensure both devices can communicate on the local network |
How do I fix double NAT?
Double NAT exists when the host is behind two routing devices, such as an ISP gateway followed by a personal router. The downstream router receives a private WAN address, so forwarding ports on that router alone cannot make FS2004 reachable from the internet.
If you administer both devices, either place the ISP gateway into a suitable bridge or passthrough mode, or forward the same UDP ports through the upstream gateway to the personal router and then from that router to the host PC. Changing gateway mode can affect every device in the home, so use another host or a trusted private virtual network if the routing arrangement is unclear.
What if the ISP uses carrier-grade NAT or IPv6-only service?
Router settings cannot create a public IPv4 address that the ISP has not assigned. Ask the provider for a reachable public IPv4 address, allow a participant with suitable service to host, or use a trusted virtual-LAN arrangement that gives invited computers mutually reachable IPv4 addresses.
A normal privacy VPN is not automatically a solution; many add another layer of NAT and block inbound connections. Choose a service designed to create a private network between trusted participants rather than exposing the host publicly.
Why can the host not test the public address from home?
Some routers do not support NAT loopback, so a computer inside the LAN cannot connect to its own public IPv4 address even though outside players can. Test locally with the LAN address and have someone on a genuinely separate internet connection test the public address while the FS2004 session is running.
Why does another player’s aircraft appear incorrectly?
FS2004 does not transfer add-on aircraft files between players. If the same model is unavailable on another computer, the remote aircraft may be replaced by a stock model, displayed incorrectly or not represented usefully.
Prove the connection with default aircraft first. Once it works, install compatible models on each computer and add complex aircraft one at a time; do not mistake a model-matching problem for a failed network connection.
Can FS2004 connect to VATSIM instead?
Yes. For FS2004, VATSIM’s supported pilot-client route is swift, which is separate from the simulator’s built-in multiplayer system.
Legacy instructions for SquawkBox or FSInn should not be treated as supported VATSIM setup advice, and vPilot is not an FS2004 client. Follow our FS2004-to-VATSIM connection guide for the simulator integration and pilot-client process.
An organised network normally uses outbound client connections, so it does not require the host-style router forwarding described above. It can also place pilots using different supported simulators in the same online airspace, but that does not make their built-in multiplayer modes cross-compatible.
Can FS2004 play online with FSX, MSFS 2020 or MSFS 2024?
No. An FS2004 direct multiplayer session accepts FS2004 participants; it cannot be joined through FSX, Microsoft Flight Simulator 2020 or Microsoft Flight Simulator 2024.
FSX has a different multiplayer implementation, while MSFS 2020 and MSFS 2024 use their own online systems. External organised networks can represent users of several supported simulators together, but they do so through separate pilot clients rather than FS2004’s DirectPlay session.
FS2004 is a civilian flight simulator, not Microsoft’s Combat Flight Simulator series. These DirectPlay instructions should not be assumed to apply to a general combat flight simulator or its multiplayer system.