Most Arma 3 dedicated-server failures fall into one of three boundaries: the server cannot be reached, Steam cannot list it, or the client is rejected after connecting. Check those boundaries in that order. Confirm a real public IPv4 address, verify the game and query ports, remove conflicting manual Steam-port settings, start the server before Steam, and then align mods, signatures and BattlEye settings.
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Start with a quick symptom check
Use the symptom that matches what you see to choose the first test. Do not change mods or reinstall until you know whether the failure occurs before connection, during the handshake or after entry.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware match| Symptom | Most useful first test | What the result means |
|---|---|---|
| Server is absent from the LAN or Internet browser | Try Direct Connect to the server’s public IP on port 2302. | If Direct Connect works, the server is reachable and the problem is listing, filtering or listing delay. |
| Direct Connect times out | Check the public IPv4 address, router forwarding, firewall rules and ICMP response. | The failure is at the network or host boundary, before Steam’s browser is relevant. |
| “Session Lost” while joining | Read the server log and compare every client and server mod version and signature. | A mismatch or failed signature check is a leading cause once basic reachability is proven. |
| “BattlEye: client not responding” | Troubleshoot the connecting computer’s BattlEye installation and security software first. | The hosting machine is not automatically at fault; this kick is commonly client-side. |
| Players connect but experience desync | Watch server CPU load while the mission is busy. | High CPU use, excessive mods or a demanding mission can be the bottleneck even when bandwidth is adequate. |
1. Confirm that the server can be reached from the Internet
You need a real public IPv4 address
The Bohemia Interactive community wiki’s dedicated-server guidance requires a public IPv4 address. An IPv6-only connection and DS-Lite tunnel are not supported for this use. A router can appear to have an Internet address while the actual host remains behind carrier-grade NAT; in that case, forwarding a port in your own router will not make the server public.
Compare the address shown by your router’s Internet or WAN page with the address shown by an external “what is my IP” service. If the two addresses differ, or the router shows a private or carrier-grade range, ask your Internet provider for a public IPv4 address or place the server on a connection that supplies one. Do this before changing Arma settings: no local configuration can overcome upstream NAT that you do not control.
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Make the host answer and permit the required traffic
The dedicated server should answer ICMP echo requests (ordinary ping) and its game traffic must be allowed through the host firewall and router. Create a forwarding rule from the router’s public side to the server computer’s fixed local address, then allow the same traffic in the operating-system firewall. Keep the local address stable with a DHCP reservation or equivalent, otherwise a reboot can silently send the forwarding rule to another device.
Test from a different network, such as a phone hotspot. Testing from inside the same LAN can give a false result when the router does not support NAT loopback. A successful local connection does not prove that an Internet player can connect.
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On Windows, the dedicated-server notes call out network discovery and the UPnP Device Host and SSDP Discovery services. If you rely on automatic port mapping, confirm those services are running and that UPnP is enabled on the router. If automatic mapping is unreliable or your network policy forbids it, use an explicit forwarding rule instead. Do not enable both approaches with stale duplicate rules and then assume the first mapping is the one Arma is using.
UPnP is a convenience, not a substitute for a public address. It cannot create inbound reachability through DS-Lite or carrier-grade NAT, and it may stop working after a router restart. Record the local server address and the mapped ports so you can verify them after any network change.
2. Start the dedicated server before the Steam client
The Bohemia Interactive guidance recommends starting the dedicated server before starting the Steam client. Starting Steam first can create Steam-port conflicts that prevent clients from connecting even though the server process appears to be running.
- Stop the dedicated-server process and exit Steam completely, including its background process.
- Confirm that the server’s configuration and executable are the ones you intend to use.
- Launch the dedicated server and wait for its console or log to show that initialization has completed.
- Only then start Steam and test a client connection.
If this order fixes the problem, keep it as part of the host’s startup routine. A scheduled task or service can launch the server first, while Steam remains a separate, later step for administration.
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3. Remove conflicting manual Steam-port settings
Arma 3 uses a game port plus Steam query ports. A hosting-provider guide describes the automatic arrangement as steamPort = game port + 1 and steamQueryPort = game port + 2. For the common game port 2302, that means the adjacent ports are selected automatically.
Inspect server.cfg and any startup parameters for old, manually assigned steamPort or steamQueryPort lines. Remove obsolete manual entries rather than replacing them with another guess. Incorrect manual values can be worse than leaving the fields unset because the server may advertise a port that is not forwarded or is already occupied.
After removing the lines, restart the server, confirm which ports the process actually binds, and update the router and firewall rules to match the active game port and its two adjacent Steam ports. If you deliberately use a non-default game port, apply the same offset rather than copying a rule written for 2302.
4. Validate server.cfg syntax before investigating clients
The configuration parser is strict: one malformed line can stop startup or leave the server in a state where it never becomes joinable. A missing quote, unmatched brace, stray character or incorrectly formatted value can have the same visible symptom as a network failure.
A safe configuration check
- Make a backup of the last configuration that started successfully.
- Compare the current file against that backup one change at a time.
- Temporarily remove recently added optional lines, especially manually assigned Steam-port settings.
- Start the server and read the earliest error in the log; later messages can be consequences of the first parse failure.
- Add changes back individually, restarting after each addition.
Do not paste a configuration fragment from a different Arma version or hosting template without checking its punctuation and option names. A server that reaches the desktop or leaves a process in Task Manager is not necessarily a server that parsed its full configuration.
5. Separate browser listing problems from connection problems
Allow for listing delay
The Steam server browser does not update in real time. The low.ms dedicated-server guide says a restarted server can take a minute or two to appear through Steam’s master server. Wait through that interval after a clean restart, then refresh the browser rather than repeatedly restarting the process.
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Filters can hide a healthy server. Clear password, mission, ping, player-count, version and mod filters while testing. Make sure the client is looking at the correct Internet or LAN tab and that the server’s reported version matches the client.
Use Direct Connect as the decisive test
Use Arma 3’s Direct Connect option with the server’s public IP address and port 2302 when that is the configured game port. If Direct Connect succeeds while the browser remains empty, the network path and server process are working; concentrate on master-server listing, filters, query-port settings and propagation time. If Direct Connect fails, return to public IPv4, forwarding, firewall and startup-order checks instead of trying to repair the browser.
When testing from the hosting machine, use an external network where possible. A successful connection to a private LAN address only proves local routing.
6. Fix “Session Lost” by aligning mods and signatures
Once a client can reach the server, “Session Lost” is commonly associated with a mod-version mismatch or a failed signature check. The server and every joining client must use the same mod versions, and the server’s signature files must match the content it is serving.
Build a single mod inventory
- Record the exact mod set enabled by the server, including required dependencies.
- Compare that list with the client’s enabled set; an extra client mod can be as disruptive as a missing one.
- Check that the actual files are the same release, not merely folders with the same name.
- Regenerate or replace signatures when the server’s mod files have changed.
- Restart the server after changing content so it does not retain an old file or signature in memory.
Read the server log for the first missing-file, version or signature message. Fix that item before interpreting later disconnect lines. If an unmodded test mission works, add the production mods back in small groups to identify the incompatible package instead of changing all of them at once.
7. Repair a damaged Workshop or manual mod installation
A Steam Workshop discussion reports that one broken dedicated-server setup was fixed by reinstalling the server and subscribing to the required mods through the in-browser Workshop. This is an anecdotal remedy, not a guarantee, but it is useful when the server’s files are incomplete, owned by the wrong account or were copied from a different installation.
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Use a clean rebuild only after preserving evidence
- Save
server.cfg, startup parameters, mission files and a copy of the server log. - Write down the mod names and versions that the server is supposed to load.
- Stop the server and remove only the damaged installation or mod cache, not your backups.
- Install the dedicated server again and obtain the required Workshop content through the account and method used for the server.
- Restore the known-good configuration, start without optional mods, then add the mod set in stages.
A reinstall should not be the first response to an unopened port or an IPv6-only connection; it changes files, not network reachability.
8. Check mission initialization and the autoinit parameter
If clients connect to a server that has no mission loaded, a Steam discussion user reported that adding the autoinit startup parameter helped. Treat this as a targeted, anecdotal workaround: first verify that the mission is present, named correctly in the configuration and compatible with the active mod set.
Use autoinit when the log shows a clean server start but the mission-selection or initialization stage never completes. Remove it again if it masks a configuration error or causes an unintended default mission to start; the log should remain the authority on what mission actually loaded.
9. Treat BattlEye kicks as a client-side investigation first
The message “BattlEye: client not responding” is often caused by the connecting client rather than the dedicated host. On the affected computer, close the game and Steam, verify the game installation, repair or reinstall the BattlEye component supplied with the game, and check whether antivirus or endpoint security is blocking its service.
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Test with one client that can join other BattlEye-enabled servers. If that client fails everywhere, continue on the client. If several otherwise healthy clients are kicked only by this server, compare the server’s BattlEye configuration and log, then verify that the server and clients are running compatible game and mod versions. Do not disable security software permanently; use a temporary, controlled test and restore protection immediately.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.10. Diagnose desync as a CPU and mission-load problem
The low.ms guide attributes many desync complaints to CPU pressure rather than insufficient bandwidth. Monitor the dedicated-server process while players are active and while the mission reaches its busiest state. A saturated CPU can delay simulation and network processing even when the Internet connection has plenty of unused capacity.
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Reduce load in a controlled order
- Run the same mission with optional mods disabled.
- Reduce the number of active mods, especially scripts that add frequent AI, persistence or telemetry work.
- Test a simpler mission with the same player count.
- Compare CPU load and desync messages before and after each change.
This approach distinguishes a hardware or host-load limit from a particular mission or mod. Increasing bandwidth will not correct a simulation thread that is already CPU-bound.
11. A complete recovery runbook
Follow these steps in order, recording the result of each one. The first step that fails identifies the boundary to repair.
- Identify the address: confirm the host has a real public IPv4 address, not IPv6-only service, DS-Lite or carrier-grade NAT.
- Verify reachability: from an external network, confirm the host answers ping and that the game port and adjacent Steam ports are allowed through the router and firewall.
- Stabilize the host: reserve the server’s local IP and confirm Windows network discovery, UPnP Device Host and SSDP Discovery where those services are required.
- Clean the startup: stop Steam, launch the dedicated server first, wait for initialization, then launch Steam.
- Clean the configuration: remove stale manual
steamPortandsteamQueryPortlines and checkserver.cfgpunctuation and values. - Read the first log error: correct parse, port, mission, mod or signature errors before moving on.
- Test outside the browser: try Direct Connect to the public address on port 2302 when using the default game port.
- Wait and clear filters: if Direct Connect works, allow a minute or two for Steam listing and remove restrictive browser filters.
- Standardize content: make the server and clients use identical mod versions, dependencies and signatures.
- Isolate performance: if joining works but play desyncs, compare CPU load with fewer mods and a simpler mission.
12. Do not generalize listen-server port advice to dedicated servers
A 2021 Steam thread suggested forwarding UDP ports 2302 through 2306 and enabling UPnP, but that discussion concerned listen servers and is not a verified universal rule for dedicated servers. Dedicated-server port requirements depend on the configured game port, the automatically selected Steam ports and the server’s own networking setup. Use the ports shown by the running dedicated server and its documentation rather than copying a listen-server recipe.
What to keep in the server log
Save a log from a failed start and one from a successful start. Note the exact time, the configured game port, the startup parameters, the first configuration error, the loaded mod list, signature warnings, mission initialization result and any BattlEye kick text. This turns “not working” into a reproducible boundary that can be tested after each change.
A healthy recovery has a clear sequence: the dedicated process starts without a configuration parse error, binds the intended game and Steam ports, initializes a mission, accepts Direct Connect from an external network and then appears in the browser after propagation. If any one of those stages fails, repair that stage before changing the next one.
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