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Fix an SCP: Secret Laboratory server by identifying which layer is failing: startup, direct connectivity, public-list visibility, or one player’s connection. Do not change random settings first. Capture the exact console or client error, confirm that the client and dedicated server use compatible builds, then test the server locally and from another network. A server that works on the host but not over the internet almost always needs a firewall, port-forwarding, NAT, or public-address check rather than a game reinstall.
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Classify the failure before changing anything
The same “server not working” description can mean several unrelated problems. Use the symptom and the first successful test to choose the right branch.
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Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →| What you observe | Most likely layer | First useful action |
|---|---|---|
| The dedicated process closes, crashes, or never reaches a ready state | Build, operating system, configuration, permissions, or plugin startup | Save the complete console output and verify supported versions before changing network settings. |
| The server is running, but nobody can join directly | Firewall, wrong port, bind address, router/NAT, or an unreachable public IP | Test the configured port on the host, then test the same public endpoint from another network. |
| Direct connection works, but the server is absent from the in-game list | Northwood verification or listing settings | Check verification, private status, contact_email, and online_mode. |
| Only one player cannot connect | That client’s build, firewall, ISP, VPN, DNS, or local installation | Have another player try the same endpoint and compare versions and error text. |
| The client says “The specified host is not available” | Incorrect public IPv4 address, port forwarding, CG-NAT/double NAT, or firewall | Recheck the endpoint and prove that the game port is reachable from outside your network. |
| The list displays HTTP Error 500 | Client-to-list service path, often IPv6/ISP/geolocation related | Add --ipv4 to the game’s Steam launch options and retry. |
| The console says “Specified port is not registered” | Northwood server verification did not register the endpoint | Restart for another verification attempt, remove blocking rules, then escalate with the exact details. |
Confirm supported builds and operating systems
After Update 14.0, Northwood lists the client requirement as “Windows 10/11 21H1+ (build 19043+) x64.” Its dedicated-server requirement is Windows Server 2022 or newer, or Ubuntu 22.04 or newer, both x64. Steam lists the client’s baseline as 64-bit Windows 10 21H1 or Windows 11, at least 4 GB of RAM, broadband internet, and 8 GB of storage. These are different requirements: a machine that can run the client is not automatically a supported dedicated-server host.
- Update the game client and dedicated server from the same release channel. A client that is newer or older than the server can fail before networking is relevant.
- Check that the server operating system is 64-bit and meets the current minimum. Unsupported older Windows or Ubuntu releases can produce startup failures that look like missing server connectivity.
- Record the exact game version, server version, operating system and architecture from the console before troubleshooting. Keep those details for support if the problem persists.
- If the problem began immediately after an update, first test the unmodified supported server build. Add plugins back only after the clean server starts and accepts a local connection.
When the server will not start
Read the first meaningful error
Do not rely on the final line alone. Copy the first exception, failed dependency, configuration parse error, or port-binding message, together with the lines immediately before and after it. A later “server stopped” line is usually a consequence, not the cause.
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Check the configured port and bind addresses
Find the port printed by the server console and in its active configuration. Editing a different port directory does nothing to the running instance. For a normal single-interface host, leave ipv4_bind_ip as 0.0.0.0 and ipv6_bind_ip as ::; these values listen on the available interfaces. A specific address is appropriate only when you deliberately run multiple interfaces and know which one should serve the game.
Isolate plugins and damaged configuration
- Stop the server cleanly.
- Back up the complete configuration and plugin directories.
- Disable the newest plugin or mod, especially one updated just before the failure.
- Start the server on a clean, supported build and test locally.
- Re-enable plugins one at a time, restarting after each change, until the incompatible component is identified.
LabAPI is Northwood’s official server-side plugin loader and framework. Check each plugin against both the installed server version and the installed framework version; a plugin compiled for another release can prevent startup or break networking after the process appears to launch.
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Use the actual game port
Forward and allow the port shown by the running server, not a remembered default or a port belonging to another instance. Steam documents the default dedicated/listen-server assignments as TCP local port 27015 for SRCDS RCON and UDP local port 27015 for gameplay traffic. If you changed the game port, substitute that value everywhere: server configuration, router rule, host firewall, and the address players enter. Steam also documents additional remote UDP and TCP ranges used for Steam operation; a restrictive corporate or hosting firewall may need those rules as well.
| Traffic | Default documented local port | Why it matters |
|---|---|---|
| Gameplay | UDP 27015 | Players need this path to reach the game server. |
| SRCDS RCON | TCP 27015 | Remote administration uses TCP when RCON is enabled; do not confuse it with gameplay. |
| Steam operation | Additional UDP/TCP ranges | Restrictive networks may require the ranges documented by Steam, not just the game port. |
Allow the executable through the host firewall
On Windows, open Windows Defender Firewall and allow the SCP: Secret Laboratory executable (shown as scpsl in the technical-support guidance) on both Private and Public networks. An inbound rule for only one profile can work on a home network and fail when the profile changes. Third-party endpoint-security products have their own firewalls, so create an equivalent allow rule there or temporarily disable that product only for a controlled test.
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Also create an inbound rule for the actual gameplay UDP port and, if you use remote administration, the RCON TCP port. Limit the rule to the required program and port after testing rather than leaving broad “allow all” rules in place.
Forward the port to a stable private address
- Give the server machine a DHCP reservation or another stable private IPv4 address.
- Create a router port-forward rule for the game’s UDP port to that address. Add the TCP rule only where the service requires it, such as RCON.
- Check that the router’s WAN address is the same public IPv4 address players are using. If the router shows a private or carrier-grade address, it is not the internet edge.
- If there is a second router, modem, mesh gateway, or virtual network layer, either remove the extra NAT or forward the port through every NAT device.
- Test from a different internet connection, such as a phone hotspot. A test from inside the same LAN can succeed because of NAT loopback even when outside players are blocked.
Carrier-grade NAT (CG-NAT) prevents unsolicited inbound connections even when your own router rule is correct. Ask the ISP for a public IPv4 address or use a hosting arrangement that supplies one. A VPN is not a universal fix: it may help with an ISP, hardware, or geolocation problem, but individual SCP: Secret Laboratory servers can reject VPN connections.
Verify that the process is listening
Run the check on the host while the server is running. On Windows, netstat -ano | findstr 27015 shows whether something has opened the expected port; replace 27015 with the configured value. On Linux, ss -lunp | grep 27015 checks for a UDP listener. These commands prove local binding only, not internet reachability. If no listener appears, return to the server console, port value, bind addresses, permissions, and plugin isolation.
For a TCP-only diagnostic, PowerShell’s Test-NetConnection 127.0.0.1 -Port 27015 can test the local RCON-style port. It does not prove that UDP gameplay traffic is passing. The decisive test is a real game connection from outside the host’s network.
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Interpret “The specified host is not available”
That message means the client could not reach the endpoint it was given; it does not identify which layer failed. Confirm the public IPv4 address, the port in the direct-connect entry, the router’s forwarding target, the host firewall profile, and CG-NAT or double-NAT status. If a local player can join but a player on another network cannot, focus on those external-path checks instead of reinstalling the client.
Make a working server appear in the public list
Reachability and listing are separate. Northwood’s public in-game list is the Verified List, so a server can accept a direct connection while remaining invisible there.
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- The server is private: remove the
!privatestate if you intend public listing. contact_emailis stilldefault: set a real contact address inconfig_gameplay.txtas required by the hosting guidance.online_modeisfalse: the hosting guidance states that this prevents public-list visibility. Use the supported online mode when you need the public list.
After changing a listing setting, restart the server and allow time for verification. Do not troubleshoot the router solely because the list is delayed when direct connection already works.
Fix “Specified port is not registered” verification errors
The console message Could not update server data on server list - [SECURITY VIOLATION] Specified port is not registered indicates that central verification did not accept the endpoint. The support guidance notes that the IP may already be registered with the central servers.
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- Stop and restart the server to trigger another verification attempt.
- Confirm that the advertised public IP and game port are the same values exposed by the router and firewall.
- Ensure no host firewall, upstream firewall, proxy, or security appliance blocks the verification traffic.
- Check that another server process is not using the same public IP and port registration.
- If the message returns, contact Northwood support or your hosting provider with the server IP, game port, exact console line, operating system, game/server version, and a relevant log excerpt.
Fix HTTP Error 500 on the server list
The SCP: Secret Laboratory client support instructions recommend forcing IPv4 when the server-list page reports HTTP Error 500. In Steam, open Library, right-click SCP: Secret Laboratory, choose Properties, and enter --ipv4 in Launch Options. Start the game again and reload the list.
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Edit the right configuration and plugin directories
Port-specific files are a frequent cause of changes having no effect. The documented path pattern is /.config/SCP Secret Laboratory/config/<Port>/, with analogous port-specific directories for EXILED and LabAPI plugins. On Linux, the leading dot denotes a hidden directory under the relevant user’s home directory. On Windows or a managed host, use the provider’s mapped configuration root, but retain the same port-specific relationship.
- Identify the port printed by the running instance.
- Open the configuration folder carrying that exact port number.
- Preserve each key’s spelling and indentation.
- Change only the value after the colon; do not replace the whole file with a template from another server version.
- Stop and restart after saving, then verify the new value in the console.
If a setting appears correct but the server behaves as before, you probably edited another instance’s folder, another port directory, or a file overwritten by a control panel on restart.
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A clean recovery sequence
Use this order so every test has a clear result:
- Capture the exact client message, server console error, timestamp, game version, server version and operating system.
- Confirm supported x64 operating-system versions and matching client/server builds.
- Stop plugins, back up configuration, and start a clean server.
- Verify the active game port and bind addresses.
- Allow the executable and required ports through Windows Defender Firewall or the host’s equivalent, including both Private and Public profiles where applicable.
- Confirm a local listener with
netstatorss, then make a local game connection. - Forward the game port to a stable private IP and test from another network.
- If external direct connection works, fix list visibility by checking verification,
!private,contact_email, andonline_mode. - Re-enable plugins individually and keep the first component that reproduces the failure disabled until a compatible release is available.
When self-hosting remains unreachable
A managed host can remove CG-NAT and router administration, but it does not remove the need to verify versions and plugins. Compare providers on the points that affect this specific failure:
| Decision point | Questions to ask |
|---|---|
| Version support | Does the service offer the current SCP: Secret Laboratory release and update it promptly? |
| Location and latency | Where is the server region, and can players reach it without an avoidable long-distance route? |
| Verification | Who handles Northwood verification, and what information is required when registration fails? |
| Network control | Can you set the game port, firewall rules, bind behavior, and RCON access? |
| Plugins and frameworks | Are LabAPI and the required plugin versions supported, and can you restart into a clean build? |
| Diagnostics | Do you receive live console logs, historical logs, backups, and restore controls? |
| Protection and support | What DDoS protection is included, and how quickly does support respond to a port or verification incident? |
Do not choose solely on an advertised price or a server-list screenshot. A host that cannot expose logs, control the actual game port, or explain its NAT and verification setup will make the same troubleshooting harder.
Escalate with evidence
Northwood says its official Discord is the main communication channel and directs users to its support site for FAQs and ban appeals. For a verification case, use the listed server-verification contact or your hosting provider. Include the server’s public IP, game port, exact error text, operating system and version, client/server versions, whether local and external tests succeeded, and the smallest relevant console or log excerpt. This lets support distinguish a registration conflict from a blocked port instead of sending you through generic reinstall steps.
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