To make an AssettoServer host reachable from outside your home network, forward 9600/TCP, 9600/UDP, and 8081/TCP on your router to the PC running the server, then allow AssettoServer.exe through the host firewall. Start the server, use the join link printed by its console, and have an outside player test it. If the log says ERROR, INVALID SERVER, CHECK YOUR PORT FORWARDING SETTINGS, one of those forwarding or firewall controls is still wrong.
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What you need to forward
AssettoServer’s documented defaults use three inbound rules. Two carry the game traffic and one carries the server’s HTTP service:
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| External port | Protocol | Forward to | Purpose |
|---|---|---|---|
| 9600 | TCP | The host PC’s private IPv4 address | AssettoServer game connection |
| 9600 | UDP | The host PC’s private IPv4 address | AssettoServer game traffic |
| 8081 | TCP | The host PC’s private IPv4 address | AssettoServer HTTP service |
Forwarding a port means telling the router where an unsolicited connection arriving on your public internet connection should go. It does not automatically permit the traffic through Windows Firewall. The router rules and the computer’s firewall rule are separate controls, so both must be configured.
This procedure concerns Assetto Corsa running with the AssettoServer project. Assetto Corsa EVO is a different game with separate server software and ports; do not apply these values to EVO.
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Before you create rules
Choose the computer that will host the server
Run AssettoServer on a PC that stays powered on and connected to the same router whose public connection your friends will use. The forwarding destination must be that PC’s private IPv4 address, not your public address.
Find the address in Windows with ipconfig and note the IPv4 address for the active Ethernet or Wi-Fi adapter. It commonly belongs to a private range such as 192.168.x.x, 10.x.x.x, or 172.16.x.x–172.31.x.x. Ignore disconnected adapters, virtual adapters, and IPv6 addresses when entering the router rule.
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A DHCP lease can change after a reboot or lease renewal. If the router later gives the host a different address, the forwarding rules still point at the old computer address and the server appears offline. Reserve the address for the host in the router’s DHCP reservation or “static lease” area. An equivalent local configuration can also keep it stable, but the exact method depends on the network equipment. This is practical networking guidance rather than a universal AssettoServer project requirement.
Record the host address, the router’s administrator address, and the account needed to change network settings before you begin. Do not confuse the router’s private address with the public address your friends use to reach your internet connection.
Confirm AssettoServer’s ports
Open the server configuration you intend to run and verify that its game service uses port 9600 for both TCP and UDP and its HTTP service uses 8081/TCP. These are the documented defaults. If you deliberately changed a value, the router and firewall rules must use the changed value instead; forwarding 9600 while the process listens somewhere else cannot work.
AssettoServer can be launched in two ways:
| Approach | Best for | Trade-off |
|---|---|---|
| Content Manager preset | Getting a configured server running quickly from an existing Assetto Corsa setup | Convenient, but the preset and launcher environment are tied more closely to that installation |
| Dedicated AssettoServer folder | Portable, repeatable, or more advanced installations | Requires you to manage the folder and launch AssettoServer.exe yourself |
The forwarding procedure is the same either way because the router only cares which computer and listening ports receive the traffic.
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Create the three router port-forwarding rules
Router menus vary substantially by model and internet provider. Look for Port Forwarding, NAT, Virtual Server, or a similarly named section. The AssettoServer guide does not prescribe a universal click path because there are effectively unlimited router and ISP combinations. Use the router’s manual or search for the router model and ISP name if the menu is unclear.
- Sign in to the router. Open its administration page from a device on your home network and enter the administrator credentials.
- Open the forwarding page. Select Port Forwarding, NAT, Virtual Server, or the equivalent feature. Avoid a similarly named outbound “port triggering” page unless your router specifically requires it for permanent inbound rules.
- Add the TCP game rule. Set the external/start and internal/end port to
9600, choose TCP, and enter the host PC’s reserved private IPv4 address as the destination. - Add the UDP game rule. Create another entry for external and internal port
9600, this time choosing UDP, with the same destination address. - Add the HTTP rule. Create a third entry for external and internal port
8081, choose TCP, and send it to the same host address. - Save or apply. Some routers require a separate Apply, Save, or reboot action. Wait until the router confirms the rules are active.
Use distinct names such as AssettoServer-9600-TCP, AssettoServer-9600-UDP, and AssettoServer-8081-TCP. Labels are for your reference; they do not change how the ports work. If the interface has separate “external” and “internal” fields, keep the same number in both fields for each rule.
Allow the server through Windows Firewall
When Windows Firewall or Windows Defender asks whether to allow AssettoServer, allow the application on the network profiles you actually use. If the server was already installed and no prompt appeared, create an inbound firewall exception for AssettoServer.exe.
The exception must apply to the executable that you launch. A shortcut, Content Manager preset, or a second copy in another folder may point to a different executable, so check the path if several installations exist. A router rule that points correctly can still fail when the host firewall silently drops the connection.
- Confirm that the exception is an inbound rule, not only an outbound permission.
- Permit both TCP and UDP traffic needed by the server, or permit the application when Windows offers an application-based rule.
- After changing the firewall, restart AssettoServer so the process is listening under the intended configuration.
- Do not disable the firewall globally as a substitute for a specific exception.
Launch the server and read the log
Dedicated-folder launch
Open the folder containing the intended installation and run AssettoServer.exe. Keep the console visible while testing. It shows startup information, registration attempts, and the join link generated for players.
Content Manager launch
Run the configured server preset from Content Manager. Verify that the preset uses the same AssettoServer installation and configuration in which you checked the 9600 and 8081 values. Starting a different preset can make you troubleshoot the wrong folder or process.
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Recognize the forwarding error
An incorrect or incomplete setup can produce this message:
Error during Kunos lobby registation: ERROR, INVALID SERVER, CHECK YOUR PORT FORWARDING SETTINGS
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Give outside players the correct join link
Do not use Content Manager’s Invite button blindly. The documented warning is that the button can copy the host’s local IP address, which is useful only inside the same local network and is unreachable for people on the internet.
Copy the link generated in the AssettoServer console instead. Share that console-generated link with friends outside your network. A player on your home Wi-Fi may be able to connect with a local address even when the public path is broken, so a genuine outside test is important.
Local versus outside testing
- Local test: a second device on the same home network checks that the server process and local firewall permit connections.
- Outside test: a friend on a different internet connection uses the console link and confirms that the public route reaches the server.
Testing from a phone’s cellular connection or asking a friend elsewhere avoids the misleading result that can occur when a router does not support connecting to its own public address from inside the LAN.
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Diagnose a server that still appears invalid
Check the destination address first
Run ipconfig again and compare the active adapter’s IPv4 address with every forwarding rule. A changed DHCP address is one of the most common reasons a previously working server stops receiving traffic. Correct the reservation or update the rules, then restart the server.
Check all protocols, not just port 9600
Port 9600 requires two entries: one TCP and one UDP. A single “9600” rule with the wrong protocol does not replace both entries. Port 8081 is a separate TCP rule and must target the same host.
Check the host firewall separately
Temporarily changing a firewall rule for diagnosis is different from leaving the firewall disabled. Confirm that the inbound exception names the running AssettoServer.exe, covers the required protocols, and applies to the active Windows network profile. Re-enable normal protection immediately after any controlled test.
Check that the process is listening
Make sure the server window remains running and that you launched the intended copy. If the process exits, reports a configuration error, or uses a different configuration than expected, no router rule can deliver a working session. Read the console from startup through the lobby-registration attempt.
Check the link you shared
Ask the outside player to use the link printed by the server console, not a link copied from Content Manager’s Invite control. A local address in the link will not route across the public internet.
Consider network topology only after the basic checks
The available AssettoServer documentation does not establish whether a particular internet connection uses carrier-grade NAT, double NAT, or an inbound-port restriction. Those are network-specific possibilities, not confirmed causes for every failed server. If the three rules, firewall exception, stable address, running process, and console link are all correct but an outside connection still cannot reach the host, inspect whether there is a second router between the host and the internet, whether the router receives a real public IPv4 address, and whether the ISP blocks inbound connections. Your router manual or ISP support can identify the appropriate diagnostic for that equipment.
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Understand the router layouts you may encounter
Different firmware may ask for slightly different fields. Map them to the same values:
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| Router field | Value for the game TCP rule | Value for the game UDP rule | Value for the HTTP rule |
|---|---|---|---|
| Service or rule name | Any descriptive name | Any descriptive name | Any descriptive name |
| External/WAN port | 9600 | 9600 | 8081 |
| Internal/LAN port | 9600 | 9600 | 8081 |
| Protocol | TCP | UDP | TCP |
| Internal host/server IP | The host PC’s stable private IPv4 address | ||
If the router offers a single “TCP/UDP” choice, use it only when the interface genuinely creates both protocol permissions. Otherwise, create separate TCP and UDP rules so you can verify each one independently. If it asks for a port range, enter the same start and end value rather than opening a wider range.
Security and maintenance considerations
Port forwarding exposes selected services from your home network to unsolicited internet traffic. Forward only the three documented ports, keep AssettoServer and Windows updated, and avoid broad “DMZ host” settings that expose the entire computer. Use a dedicated Windows account or server folder when practical, and do not share router administrator credentials with players.
Keep a short record of the host’s reserved address, rule names, AssettoServer folder, and configuration values. If you replace the router, change ISP equipment, move from Wi-Fi to Ethernet, or reinstall the server, this record makes it easier to reproduce the setup without accidentally forwarding to an obsolete address.
When you no longer host publicly, remove or disable the three forwarding rules and the associated firewall exception if it is not needed for another purpose. A rule that remains after the server is gone serves no useful function.
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AssettoServer’s feature scope
AssettoServer is a custom server aimed at freeroam-oriented use. Its project introduction says that race sessions, qualifying sessions, and lap times are not supported yet. Port forwarding only makes the service reachable; it does not add those unsupported workflows. If your group specifically needs conventional race or qualifying administration and lap-time handling, confirm that the server implementation you choose supports those functions before spending time on network configuration.
Complete verification checklist
- The server PC has a stable private IPv4 address.
- The configuration uses 9600/TCP, 9600/UDP, and 8081/TCP, unless you intentionally changed the ports and matched every rule to those changes.
- The router forwards each protocol and port to the server PC’s current private address.
AssettoServer.exehas an inbound Windows Firewall exception.- The intended AssettoServer instance is running from the correct folder or Content Manager preset.
- The console does not continue to report the invalid-server registration error.
- Players outside the home network receive the console-generated link, not a local-IP Invite link.
- An outside player has tested the connection from a different internet connection.
If every item is true and the server remains unreachable, the remaining investigation is specific to the router and ISP path. Gather the router model, whether another router sits upstream, and the address shown on the router’s internet/WAN page before contacting the ISP or consulting its documentation.
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