When a Space Engineers server is visible but will not let you join, check the exact game build on the server and every client first. A version mismatch is the most frequently reported cause. If the versions match, the next priority is the server’s UDP port (27016 by default) on both the router and the server computer’s firewall. Only after those checks should you change MTU settings, disable network utilities, clear caches, or remove mods.
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This guide separates failures that affect a local connection from failures that affect Internet players, gives an ordered recovery procedure, and identifies which community fixes are anecdotal rather than confirmed by Keen Software House.
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The same “server not responding” symptom can be produced by different layers: an incompatible build, a blocked port, a damaged local file, or a mod that sends too much data during connection. Use the symptom that best matches your case to choose the first test.
| What you observe | Most likely area | First action |
|---|---|---|
| The join message says the host denied access because of a version mismatch. | Server and client builds are different. | Set the dedicated server and every player’s Steam Betas setting to None, update, and compare the displayed version numbers. |
| You can join on the same LAN, but friends outside your home cannot. | Router forwarding, firewall, or a changing server-PC address. | Forward UDP 27016 to the server PC, allow it through the OS firewall, and make the PC’s local address stable. |
| No one can join, including from the server’s own machine. | Version, server process, files, or local firewall. | Verify versions, test a local/Direct Connect attempt, and validate files before changing the router. |
| The server appears in a browser but clients time out while loading. | Large mod or plugin payload, or a network path problem. | Temporarily test an unmodded world and disable optional preload features. |
| Only one player fails while others join. | That player’s branch, files, cache, or background network software. | Check that player’s Betas setting and files, then test with overlays and network optimizers disabled. |
Do not change several variables at once. A one-change test leaves you with a result you can interpret.
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1. Make the server and clients run the exact same version
Keen Software House support says a dedicated server and every connecting client must use the same game version, even when no one changed a mod. Steam can update a desktop client while a dedicated-server installation remains on an older build. The support guidance is summarized in Keen’s version-mismatch discussion: Keen version-mismatch support thread. A separate Keen thread links the same issue to widespread “server not responding” reports: Keen server-not-responding thread.
Reset the Steam branch on the dedicated server
- Close the dedicated server and any running game client.
- In Steam, open the dedicated-server tool’s Properties.
- Open the Betas tab and select None. This returns the installation to the normal branch rather than a test branch.
- Allow Steam to finish downloading, then start the server once so it writes the updated files.
Reset every player’s branch
- For the base game in Steam, open Properties and then Betas.
- Set the selection to None for every player who cannot connect.
- Let Steam complete the update before launching the game.
- Check that the server’s mod list and the client’s subscribed/enabled mods are identical. A matching base-game build does not make an incompatible mod set valid.
The denial dialog can show both numbers. One player reported an example of “Your version: 1204015; Server version: 1204017” in this Steam discussion: version-denial report. Update the side with the lower number, then recheck rather than assuming the newest-looking installation is correct.
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Stop the server completely and verify that Steam is updating the same dedicated-server directory that you launch. As a last-resort community report, one administrator closed the server, removed the dedicated-server files, and reinstalled them; that fixed the mismatch for that installation. This is a single-user report, not a guaranteed remedy, so copy your worlds, configuration, and scripts before removing anything.
When the fault is on an official server
If the problem occurs on an official public server, the host may be running the incompatible build. Check whether other players report the same outage before changing your own installation. A local reinstall cannot repair a host-side mismatch.
2. Open the listening port for Internet players
The default dedicated-server listening port is UDP 27016. It can be changed in the server configuration tool. For players outside your home network, the router must forward incoming traffic on that UDP port to the computer running the server, and the computer’s operating-system firewall must allow it.
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Give the server PC a stable local address
Port-forward rules target an internal address such as 192.168.1.25. If the router later gives the server PC a different address, the rule points at the wrong device. A forum answer identifies a static address for the server PC as necessary for a forwarding rule to remain valid; treat that advice as low-confidence community guidance and use a DHCP reservation when your router offers one. The discussion is at Steam LAN/public-server thread.
Create the Windows firewall rule
Run an elevated Command Prompt on the server PC and allow the same UDP port:
netsh advfirewall firewall add rule name="Space Engineers Dedicated Server" dir=in action=allow protocol=UDP localport=27016The advfirewall form is the current syntax shown in this community guide: Steam dedicated-server networking guide. The older netsh firewall syntax is obsolete. If you selected a non-default server port, substitute that number in both the router rule and the firewall rule.
Forward the port in the router
- Log in to the router’s administration page.
- Create a port-forward entry for UDP 27016 (or your configured port).
- Set the destination to the server PC’s reserved local address.
- Save/apply the rule and restart the server process.
- Test from a different Internet connection, such as a phone hotspot; testing from inside the same LAN can produce misleading results because some routers do not support NAT loopback.
Multiple servers on one computer
Each running instance needs a unique port. Forwarding one port to two processes cannot work reliably; assign a separate port in each configuration and create a corresponding firewall rule and router entry.
What about TCP or UDP 27015?
The available guidance is inconsistent. Keen’s reported direction specifies UDP, while one discussion claims both UDP and TCP and another guide mentions UDP 27015 for discovery. Those extra requirements are not confirmed in the supplied Keen material. Start with the documented UDP 27016 listener, then consult the game’s current dedicated-server documentation if packet captures or logs show a different port. Do not expose additional ports blindly.
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3. Separate a LAN problem from an Internet problem
A server visible on LAN proves that the process is advertising locally; it does not prove that the router is accepting unsolicited Internet traffic. Use these tests in order:
- Join from the server PC. If this fails, concentrate on the server process, version, files, and local firewall rather than port forwarding.
- Join from another computer on the same LAN. A successful LAN join indicates that the world and basic local networking work.
- Try Direct Connect from a remote network. Have a friend use the public address and forwarded port. If LAN works but this fails, inspect the router rule, the server PC’s address, and the ISP’s inbound filtering.
- Compare with another player. If one person cannot join while others can, troubleshoot that player’s branch, files, cache, or background software.
When an official public server is failing for many people at once, wait for host-side recovery rather than repeatedly reinstalling your clients.
4. Test less-common network causes one at a time
Router MTU
A single Tom’s Hardware forum report blamed an MTU of 1400 between the router and an ISP gateway; changing it to 1500 restored connectivity: MTU report. This is an anecdote, not a game-wide requirement. Test MTU only after versions and port forwarding pass. Record the original value, change one device at a time, and revert immediately if other Internet services degrade. Your ISP may require a lower MTU for a particular tunnel, so do not assume 1500 is universally correct.
Network optimizers and overlays
One player reported that ASUS ROG GameFirst blocked multiplayer connections. Temporarily exit network-prioritization tools, gaming overlays, packet filters, and “optimizer” utilities, then retry. The report is documented in this Steam troubleshooting thread: GameFirst connection report. If disabling a utility fixes the problem, add an exception for the game and server rather than leaving security software disabled permanently.
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A community reply describes connection problems when the dedicated server and the game run on one computer and suggests a separate machine. This is low-confidence advice, not a stated hardware requirement: same-PC hosting discussion. Test a separate computer only after the lower-risk checks pass. If the separate host works, compare firewall profiles, available memory, and which local address each process binds to.
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5. Repair files and caches safely
Use file cleanup only after recording your settings and backing up worlds. Cache deletion can remove local data that is not synchronized elsewhere.
Validate the game installation
- In Steam, open the game’s Properties.
- Choose Installed Files.
- Select Verify integrity of game files and wait for Steam to reacquire missing or damaged files.
- Restart Steam and retest the connection before deleting user data.
Clear shader and temporary content
Community fixes include deleting the game’s ShaderCache folders and the TempContent folder in the Steam installation. Another report recommends clearing most of AppDataRoamingSpaceEngineers while retaining Blueprints, Saves, and Screenshots: Steam cache-cleanup discussion. Folder names can vary by installation. Copy the entire SpaceEngineers folder elsewhere first, then remove only the cache or temporary directories you can identify. Never delete saves before confirming that a backup opens.
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Reinstall the dedicated-server files
If the server installation itself is damaged or stuck on an old build, reinstalling its files may help, as described in the single-user mismatch report above. Preserve SpaceEngineers-Dedicated.cfg, world folders, and any scripts before uninstalling. Reapply the saved configuration after Steam finishes installing.
6. Reduce mod and plugin connection payloads
A server can be reachable yet time out while sending world or mod data. Test with a new, unmodded world or temporarily disable nonessential mods to distinguish a content problem from a network problem. Change one mod group at a time so you can identify the offender.
In a Steam Workshop discussion, a Torch administrator reported that disabling Essentials’ planet-data preload reduced client data from about 26 MB to under 1 MB and stopped timeouts for that server’s users: Torch planet-data preload report. The figures are a forum report with no stated year or independent measurement, so use them as an example of payload reduction, not as a guaranteed amount for your world. If disabling the preload helps, re-enable features one by one and monitor which setting causes the timeout.
7. A low-risk recovery sequence
Follow this order to minimize downtime and avoid destructive changes:
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- Write down the exact error text and any version numbers shown.
- Set the server and every client to Steam Betas: None, finish updates, and confirm mods match.
- Attempt a join from the server PC, then from another device on the same LAN.
- If LAN works but remote users fail, reserve the server PC’s local address, forward UDP 27016, and add the Windows firewall rule.
- Test one remote connection from a different Internet service.
- Temporarily disable network optimizers and overlays.
- Validate Steam files; back up saves before clearing shader or temporary folders.
- Test an unmodded world and disable heavy preload/plugin features.
- Only then investigate MTU or move the server to another computer.
This sequence distinguishes a build problem from an access problem before you make changes that could erase local data.
How the fixes compare
| Change | Scope | Risk and cost | Evidence strength |
|---|---|---|---|
| Set Betas to None and update | Server and all clients | Low risk; downloads required | Medium; based on Keen support guidance |
| Forward UDP 27016 and allow the firewall | Internet joins | Low software cost; requires router access | Medium; community guide and reported Keen direction |
| Reserve/static local address | Internet joins over time | Low; router configuration | Low; forum guidance |
| Disable overlays or optimizers | Affected client or host | Low; reversible | Low; single-player report |
| Validate files or clear caches | Affected installation | Low to medium; backup required for user data | Low; community reports |
| Disable mod preload/features | Servers with heavy content | Low; may remove a feature temporarily | Low; one Torch administrator’s report |
| Change MTU or move to another PC | Specific network or host | Medium; can affect other traffic or require hardware | Low; anecdotal reports |
What to send Keen support if nothing works
Collect the information before opening a support request. Keen asks for the server configuration file SpaceEngineers-Dedicated.cfg, located in the AppDataSpaceEngineersDedicated folder, a list of recent mod, setting, or system changes, and whether you can join over LAN or Direct Connect. The request checklist appears in Keen support topic 48608.
- Attach the current configuration file, after removing passwords or private addresses if necessary.
- State whether the server is visible, whether LAN joining works, and whether Direct Connect from outside the LAN works.
- Include the exact version numbers from the denial message and the Betas setting on both sides.
- List every recent mod, plugin, preload, router, firewall, MTU, or operating-system change.
- Describe which troubleshooting step changed the symptom and which did not.
Current branch names and version numbers can change, so rely on the numbers Steam displays on the day you troubleshoot rather than an old screenshot or forum post.
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