If a Factorio server is not responding, first prove that the server process has loaded a save and accepts a local connection. Then verify that every client has the same game version and mods, and finally test the Internet path: Factorio uses UDP only, with 34197/UDP as the default port. A local connection that works while an Internet connection fails points to port forwarding, a firewall, Docker publishing, an incorrect address, or ISP NAT—not usually to the Factorio simulation itself.
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What “server not responding” usually means
Factorio can fail at several different layers, and the error message does not identify which layer failed. The practical way to diagnose it is to move outward from the server:
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- Application: the dedicated process did not start, could not load the save, or is listening on a different port.
- Compatibility: the client and server are on different game versions or have different mods.
- Host network: the operating-system firewall, antivirus, or security group is dropping traffic.
- Router or container network: the port is not forwarded, is forwarded to the wrong private address, or is published with the wrong protocol.
- Internet edge: the address being shared is private, the ISP uses carrier-grade NAT (CGNAT), or the connection does not provide an inbound public path.
Do not begin by changing router settings. A local test tells you whether Factorio is working before you spend time on the public-network boundary.
1. Confirm the dedicated server is running and has a save
Start the headless server with a known save
A dedicated instance is started with the --start-server option followed by the save file. For example:
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factorio --start-server my-save.zipUse the executable and working-directory conventions for your operating system. Keep the server console visible while testing. It should show that the save was opened and that the server is listening. If the process exits, reports a missing save, or shows a bind/listen error, fix that first; router changes cannot make a stopped process reachable.
Test from the same machine
Use a Factorio client on the server computer and connect to localhost (or 127.0.0.1) on the configured port. The command-line reference also supports a direct connection test with:
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Test from another device on the LAN
From a second computer on the same home or office network, connect to the server’s private LAN address, such as its 192.168.x.x or 10.x.x.x address, using the configured Factorio port. Do not use the public address for this test. Some routers do not support hairpin NAT (also called NAT loopback), so a public-address test from inside the same network can fail even when Internet access is correctly configured.
If localhost fails, troubleshoot Factorio itself. If localhost works but the LAN test fails, inspect the host firewall, the private address, and whether the server is bound to the expected interface. If LAN works, proceed to the Internet checks below.
2. Make versions and mods identical
Every game instance joining a multiplayer session must use exactly the same game version and mods. This is a compatibility requirement, not a port-forwarding issue. The official multiplayer guidance states: “All game instances need the installation of exactly the same game-versions and mods.”
Check the game version
- Read the version displayed by the server and by each client.
- Ensure that an automatically updated client has not moved ahead of a server that was left on an older build.
- If the server is managed through a script or container image, verify which Factorio version that image actually starts.
Check the complete mod set
- Compare mod names and versions, not just the number of installed mods.
- Install or remove mods until the lists match exactly on the server and every client.
- After changing mods, restart the server and reconnect; a running process may still have the previous set loaded.
Resolve version and mod mismatches before investigating forwarding. A perfectly reachable server can still reject a client that does not match.
3. Use UDP and the correct port
Factorio uses UDP only for multiplayer traffic. The default server port is 34197/UDP, although the port can be changed in the server configuration. Do not forward only TCP 34197: a TCP-only rule does not satisfy Factorio’s traffic requirement.
Record the actual configured port
Write down the port shown in the server configuration or startup output. If you changed it from 34197, use the new value consistently in the server, firewall, router, Docker mapping, and client connection. A common failure is forwarding 34197 while the process is listening on another port.
Allow the port on the host
Create an inbound firewall rule for the configured UDP port on the computer running Factorio. Check both the operating-system firewall and any antivirus or endpoint-security product that includes network filtering. If the host is a virtual machine or cloud instance, also check its provider-level security group or network ACL.
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When testing, avoid disabling all security controls permanently. A narrowly scoped UDP rule for the Factorio port is safer and makes the final configuration easier to audit.
4. Separate LAN problems from Internet problems
| Observed result | Most likely boundary | Next action |
|---|---|---|
| Localhost cannot connect | Factorio process, save, or local bind | Review startup output, save path, and the configured port. |
| Localhost works; LAN client cannot connect | Host firewall, private address, or interface binding | Allow UDP on the host and connect to the server’s LAN address. |
| LAN works; Internet clients cannot connect | Router forwarding, public address, firewall, Docker, or ISP NAT | Verify the WAN address, UDP forwarding, and whether the ISP permits inbound traffic. |
| Some Internet networks work and others fail | Address-family, ISP, or network-policy difference | Compare the working and failing networks and check the public path with the ISP or host. |
The official multiplayer guidance requires a publicly accessible IP for Internet play behind NAT, or a port-forwarding solution. LAN players should use the server’s private LAN address. A public address copied from a “what is my IP” page is useful only if it is the address assigned to the router and the ISP is not placing another NAT layer in front of it.
Find the correct private address
Give the router a stable destination for the server. If the server’s private address changes through DHCP, a forwarding rule can silently point to the wrong machine the next day. Use a DHCP reservation in the router or a carefully configured static address, then confirm that the forwarding rule targets that address.
Compare the router’s WAN address with the observed public address
Log in to the router and note its WAN or Internet address. Compare it with the public address shown by an external service. If the router shows a private-range address or an address different from the observed public one, another NAT device may be upstream. In that situation, you may need forwarding on the upstream device, bridge mode, or an alternative hosting arrangement. If the upstream NAT is controlled by the ISP, you may be behind CGNAT and unable to accept unsolicited inbound connections through ordinary home-router settings.
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- Assign the server computer a stable private LAN address.
- Open the router’s port-forwarding or virtual-server page.
- Create a rule for the configured Factorio port, using UDP as the protocol.
- Set the destination to the server computer’s private address, not the router address and not another device.
- Save or apply the rule, then confirm that it remains present after the router reloads.
- Keep the client’s address format straight: LAN users connect to the private address; remote users connect to the public address and forwarded port.
If the server uses a non-default port, forward that port rather than 34197. Some router interfaces offer “TCP/UDP” as a combined option; because Factorio is UDP-only, a UDP-specific rule is clearer, while a combined rule is acceptable only if the router still forwards UDP correctly.
Do not test the public path only from inside your home
Use a friend on another network, a mobile hotspot, or another external connection. A failure from a computer on the same LAN may be caused by missing NAT loopback rather than a broken Internet configuration. Conversely, a port-checking website that tests TCP is not evidence that a UDP Factorio port is reachable.
6. Check Docker and other network layers
Containerized servers add another boundary between the Internet and Factorio. The port must be published from the host to the container with the UDP protocol, and the container must expose the same port on which Factorio listens.
Verify the mapping
- Confirm the container is running and that its logs show a loaded save and a listening server.
- Check the host-to-container mapping for the configured port and protocol. A mapping that publishes only TCP is wrong for Factorio.
- Ensure the router forwards to the Docker host’s private address, not to an internal container address that the router cannot route to.
- Check host firewall rules in addition to container settings.
For a conventional mapping, the syntax commonly includes the protocol suffix, such as 34197:34197/udp; adapt it to the image’s documented configuration and the port you actually selected. Do not assume that a container’s internal port is automatically visible on the LAN.
Account for server-browser detection
Container documentation notes that port mappings can affect how the server browser detects a server port. If direct connection works but browser discovery does not, compare the externally published UDP port with the port advertised by the server and the port configured in the container. Treat browser visibility and direct reachability as separate tests.
7. Use controlled diagnostics instead of random changes
Change one boundary at a time
Keep a short test record: client location, address used, port, result, and any console message. Start with localhost, then LAN, then an external network. If you change the server port, firewall, and router at once, you will not know which change mattered.
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Use an external player as the decisive WAN test
Ask a player outside your home network to connect directly to the public address and configured UDP port. Have them retry after the router rule is applied and after the server is restarted. A direct external test is more meaningful than a local scan because it crosses the NAT boundary that is failing.
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A March 2025 Factorio forum discussion suggested checking firewall rules, trying a local client, and using an SSH tunnel as a diagnostic when a direct UDP connection receives no response. Treat that as a troubleshooting idea, not a universal fix. Basic SSH forwarding is primarily TCP-oriented and does not magically turn a blocked UDP path into a permanent Factorio solution. If you use a tunnel, document exactly what is being forwarded and use it only to isolate whether the direct network path is the problem.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.8. Recognize common failure patterns
“Could not establish network communication” immediately
First verify that the server is still running and that the client is using the right address and port. Then check version and mod equality. If the client is remote, confirm UDP forwarding and the host firewall before changing any game settings.
Server appears in a list but joining fails
Discovery does not guarantee that the advertised endpoint is reachable. Check the published UDP port, Docker mapping, router destination, and whether the server is advertising a stale or private address.
It worked yesterday but not today
Check for a changed private address, an automatic game or mod update, a changed public address, a router reboot that removed a rule, or a server process that stopped after a save or system restart.
Only one friend cannot join
Have that player verify their game version and mods first. If other remote players can connect, the server’s forwarding is probably functional and the remaining issue may be the friend’s local firewall, network policy, or address entry.
LAN players work while every remote player fails
This is the classic public-boundary case. Recheck UDP forwarding, the host firewall, the router’s WAN address, Docker publication, and CGNAT. Do not keep reinstalling Factorio when the LAN test already proves that the local process is reachable.
9. Decide whether self-hosting is still the right remedy
Self-hosting is appropriate when you want full control of saves, mods, versions, backups, and operating-system settings, and you can provide a reachable public network path. It also requires you to maintain the router, firewall, server updates, storage, and recovery plan.
Managed Factorio server hosting can remove router, firewall, and operating-system administration. It does not remove the need to verify compatibility or understand how your saves and mods are handled. Evaluate a provider using the following questions before moving a world:
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| Decision area | Self-hosted server | Managed hosting |
|---|---|---|
| Internet reachability | You configure public addressing, forwarding, and firewall rules. | The provider normally supplies the Internet-facing endpoint. |
| Administration | You maintain Linux, Windows, or Docker and all updates. | The provider handles the platform; your control depends on the plan and panel. |
| Mods and versions | Maximum control, but you must keep every client aligned. | Check which Factorio versions, mod installation methods, and mod limits are supported. |
| Saves and backups | You choose storage and backup frequency and retain direct files. | Confirm backup schedule, retention, restore process, and whether you can download the save. |
| Performance | Depends on your hardware, connection, and concurrent players. | Ask about allocated resources, player limits, and upgrade options. |
| Cost and support | Uses existing hardware and your time. | Recurring charges and support quality vary; verify current regional terms directly. |
Move to managed hosting only after deciding that the recurring cost and reduced administration outweigh the control of your own machine. Preserve a local copy of the save before migration.
10. A concise recovery checklist
- Keep the server console open and start it with
--start-server SAVE. - Connect locally with
localhost; if that fails, fix the process or save. - Connect from another LAN device using the server’s private address.
- Make game versions and mod lists exactly identical.
- Record the configured port; default Factorio traffic is UDP 34197.
- Allow that UDP port through the host firewall and any cloud security group.
- Forward the same UDP port from the router to the server’s stable private address.
- If using Docker, publish the UDP port on the host and forward the router to the Docker host.
- Compare the router WAN address with the externally observed public address.
- Test from a genuinely external network, not only from inside the LAN.
- If LAN works but WAN never does, investigate upstream NAT or CGNAT and consider a managed server.
What the successful result looks like
A healthy setup has a running server process with a loaded save, matching game versions and mods, a client that can connect over the LAN, and an external player that can reach the configured UDP port through the public address. Each layer has a single, consistent port and address: Factorio listens on the server, the host firewall permits UDP, Docker (if present) publishes UDP, the router forwards UDP to the correct private machine, and the ISP provides a usable inbound public path. When those conditions are met, “server not responding” is no longer a mystery message; the failing boundary is identifiable and repairable.
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