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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsTo let players outside your home network join an AssettoServer session, forward the server’s documented game and HTTP ports from your router to the PC running the server, then allow AssettoServer.exe through the host computer’s firewall. The router rules and the Windows firewall exception are separate requirements. Finally, give friends the join link generated by the server console—not a Content Manager invite link that contains your private, local IP address.
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Which ports an AssettoServer host needs
The current beginner setup documented for AssettoServer uses three inbound rules. All three rules must point to the same computer’s private IPv4 address. Create separate entries for TCP and UDP even when your router offers a combined “TCP/UDP” choice; selecting both protocols is acceptable only if the router clearly applies both protocols to the same port.
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| External port | Protocol | Forward to | Role |
|---|---|---|---|
| 9600 | TCP | The PC running AssettoServer | Assetto Corsa game traffic |
| 9600 | UDP | The same server PC | Assetto Corsa game traffic |
| 8081 | TCP | The same server PC | AssettoServer HTTP service |
These are the documented defaults represented by the AssettoServer configuration. If you deliberately changed a port in your server configuration, the router rule must match that changed value; do not blindly forward the defaults while the server is listening elsewhere. The guide does not provide a universal router screen because menus differ between router models and internet providers.
What port forwarding actually does
A home router normally keeps devices on a private network and does not accept unsolicited connections from the internet. Port forwarding creates a NAT (Network Address Translation) rule: traffic arriving at a specified public port is sent to one private IPv4 address inside your network. In this case, the destination is the Windows PC that runs AssettoServer.
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Forwarding is not the same as opening a port in Windows. The router can deliver a packet to the PC while Windows Firewall still blocks the application, or Windows can allow the application while the router sends traffic to the wrong device. Both controls must be correct. Port forwarding also does not make a private address publicly routable; friends outside your home network need the server’s externally usable join link.
Before changing the router
Identify the server computer’s private IPv4 address
On the PC that will host AssettoServer, identify its local IPv4 address. In Windows, opening Command Prompt and running ipconfig displays the address under the active Ethernet or Wi-Fi adapter. Use the IPv4 address for the network connection that actually reaches your router, not a VPN adapter, virtual machine adapter, or disconnected interface.
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Keep the host on the same network
Do not create a rule for an address belonging to a different computer, a guest network, or a second router. If the host moves from Ethernet to Wi-Fi, the adapter may receive a different private address and the old forwarding rule will no longer reach it. A reserved address tied to the adapter you use for hosting prevents that common failure.
Decide how you will launch the server
AssettoServer can run directly from a dedicated folder or through a preset in Content Manager. Choose one method before troubleshooting so that you know which configuration and executable are active. A Content Manager preset and a separately launched folder can use different settings, including different port values.
Confirm AssettoServer’s configuration
- Open the configuration used by the instance you intend to publish.
- Verify that the game ports correspond to
9600for both TCP and UDP. - Verify that the HTTP port corresponds to
8081over TCP. - If you changed any value, record the actual value and use it in the router rules instead of the default.
- Save the configuration and close any duplicate server instance before testing.
The three documented defaults are a starting point, not a guarantee that every custom preset still uses them. A port-forwarding rule can only work when the server is listening on the same port and protocol that the router forwards.
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Create the router forwarding rules
Open the administration page for the router that is directly connected to your internet service. Look for a section named Port Forwarding, NAT, Virtual Server, or a similar term. Because there are many router and ISP combinations, the exact labels, login process, and save buttons vary; use the router manual or search for instructions using your router model and ISP name.
- Sign in to the router’s administrator interface.
- Open the port-forwarding, NAT, or virtual-server page.
- Create a rule for external port
9600, protocol TCP, with the destination set to the host PC’s private IPv4 address and internal port9600. - Create a second rule for external port
9600, protocol UDP, using the same destination address and internal port. - Create a third rule for external port
8081, protocol TCP, again targeting the same host address and internal port. - Enable each rule and apply or save the router configuration.
If the router asks for a service name, use descriptive names such as “AssettoServer 9600 TCP,” “AssettoServer 9600 UDP,” and “AssettoServer 8081 TCP.” The name is only an administrator label; the port, protocol, and destination address are what control traffic.
Some interfaces ask for a port range. For a single port, enter the same number as the start and end, rather than forwarding an unnecessarily broad range. Do not expose unrelated ports just because the router offers a preset for another game.
Allow AssettoServer through the host firewall
When Windows Firewall or Windows Defender prompts about AssettoServer, allow the application on the network profiles you use for hosting. If the server was already installed and no prompt appears, create an inbound exception for AssettoServer.exe in the firewall’s allowed-app or inbound-rule settings.
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The exception must apply to the executable that you actually launch. If you have multiple copies in separate folders, allowing one copy does not automatically allow another. Keep the rule limited to the required application and, where your firewall offers the choice, enable only the private network profile used by the server rather than permitting every network type.
A firewall exception does not replace the router rules. Conversely, a correct router configuration cannot bypass a host firewall that rejects the incoming connection.
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Start the server and read the log
Launch AssettoServer.exe directly from its dedicated folder, or run the intended preset from Content Manager. Keep the console or log visible while the instance starts. A successful start should show the server binding to the configured ports and attempting to register with the Kunos lobby.
If the log displays the exact message Error during Kunos lobby registation: ERROR, INVALID SERVER, CHECK YOUR PORT FORWARDING SETTINGS, treat it as a prompt to verify the complete path from the internet to the process:
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- Check that each rule targets the host PC’s current private IPv4 address.
- Check the protocol: 9600 requires both TCP and UDP, while 8081 is TCP.
- Confirm that the active configuration still uses the forwarded ports.
- Confirm that the firewall exception names the executable you launched.
- Restart the server after correcting a configuration or firewall rule.
The misspelling “registation” is part of the displayed log text; search for the distinctive INVALID SERVER portion if you are looking through a long log.
Share the right join link
Content Manager’s Invite button can copy a link containing the host’s local IP address. That address is meaningful only inside your home network, so an outside player cannot use it. The AssettoServer guide specifically instructs hosts not to use that Invite button for internet players.
Instead, use the link generated in the server console after the server starts and registration succeeds. Copy that console-generated link exactly and send it to friends. Players on the same home network may be able to connect using a local address, but that is a different path from the publicly usable link.
Test the setup in the right order
Test from the host
First make sure the server starts without configuration errors and remains running. A stopped process cannot answer a forwarded connection, regardless of the router state.
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Test from another device on your home network
Use another computer on the same private network to establish that the server itself is reachable locally. If local access fails, inspect the AssettoServer configuration and Windows firewall before investigating the internet connection. A router cannot fix a service that is not listening or is blocked on the host.
Test from outside the home network
Ask a friend on a different internet connection to use the console-generated link. Testing from inside the same network can be misleading because some routers do not support NAT loopback (also called hairpin NAT), even when outside access works. Conversely, a local test can succeed while a forwarding rule is still wrong because local traffic may bypass the router’s public-side translation.
Troubleshoot by symptom
The server is visible locally but not to outside players
- Recheck that the router’s destination address matches the host’s current private IPv4 address.
- Verify separate TCP and UDP handling for port 9600 and TCP handling for 8081.
- Confirm the rules are on the internet-facing router, not an access point or secondary device.
- Check that the server process is still running when the outside player attempts to join.
- Send the console-generated link rather than a link copied from Content Manager’s Invite button.
The forwarding rule works until the PC reconnects
This usually indicates that the host received a different local address. Recheck the address shown by ipconfig, update the rule if necessary, and configure a DHCP reservation or equivalent stable-address arrangement.
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The log still reports an invalid server
Compare the active server configuration with every router entry, including protocol and internal port. Then inspect the firewall exception for the exact executable path. Running a second instance from another folder can make you check the wrong configuration, so close duplicates and launch only the intended copy.
Nothing changes after correct-looking rules
Some networks place another router between the host and the internet, or use carrier-grade NAT or an inbound-port restriction. The available AssettoServer documentation does not establish which of these conditions applies to any particular reader. If the three rules, the host firewall, the active configuration, and the external link are correct but outside connections still fail, identify whether the router’s public-facing address is actually assigned to your equipment and ask the ISP which inbound-connection limitations apply. Do not assume one of these blockers without checking the specific network.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Content Manager or a dedicated folder?
| Approach | Best fit | Trade-off |
|---|---|---|
| Content Manager preset | Quick setup and convenient launching for a host already managing Assetto Corsa there | It is easier to select the wrong preset or copy a local-IP invite link; verify which configuration is active. |
| Dedicated AssettoServer folder | Portable, explicit files and greater flexibility for advanced arrangements | You must manage the folder, executable, configuration, and updates yourself. |
Both approaches still require the same network path: matching server ports, router forwarding to the host, a firewall exception, and the correct externally usable link. The choice changes how you launch and maintain the process, not what the router must deliver.
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AssettoServer versus the original server workflow
AssettoServer is a custom, freeroam-oriented server implementation. Its project introduction states that race sessions, qualifying sessions, and lap-time workflows are not supported yet. That makes it a poor fit when your group’s essential requirement is a conventional race weekend with those session types and timing records.
Choose the implementation based on the driving format you need, not only on whether a port appears open. AssettoServer’s forwarding instructions in this guide apply to the documented AssettoServer setup; they should not be silently transferred to Assetto Corsa EVO, whose server tooling and ports are separate.
Home hosting and external hosting are different decisions
Forwarding ports lets your own internet connection publish the server. It does not establish a price, uptime guarantee, bandwidth allowance, or security posture for an external hosting service. The available documentation provides no provider-specific plan or performance comparison, so those factors must be evaluated separately if you decide not to host at home.
For a home host, keep the PC powered on, connected to the reserved network address, and running the same server configuration that you forwarded. If any of those conditions changes, outside players may lose access even though the router entries remain visible.
Security and maintenance checklist
- Forward only the documented ports required by your active AssettoServer configuration.
- Keep the server executable and Assetto Corsa installation updated through your normal trusted process.
- Use a firewall exception for the specific
AssettoServer.exepath rather than opening unrelated applications. - Review the destination address after replacing the network adapter, changing routers, or resetting DHCP reservations.
- Remove obsolete forwarding rules when you stop hosting or move the server to another PC.
- Do not distribute a local-IP invite link to internet players; generate the link from the server console.
Quick reference: the complete procedure
- Find the host PC’s private IPv4 address and reserve it in the router’s DHCP settings or use an equivalent stable local configuration.
- Verify the active AssettoServer configuration: 9600/TCP, 9600/UDP, and 8081/TCP unless you intentionally changed those values.
- Forward each port and protocol from the internet-facing router to that host address.
- Allow the exact
AssettoServer.exethrough Windows Firewall. - Launch the server from the intended dedicated folder or Content Manager preset.
- Inspect the log, correcting any
INVALID SERVER, CHECK YOUR PORT FORWARDING SETTINGSerror before inviting players. - Copy and share the console-generated join link.
- Have someone outside your home network test the connection.
When all three forwarding rules, the firewall exception, the active configuration, and the console-generated link agree, friends outside your network have the network path required to join an AssettoServer session.
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