Most Arma 3 dedicated-server failures come from one of six places: the server is not reachable from the internet, it was started in the wrong order, server.cfg contains an invalid line, Steam has not listed a recent restart yet, client and server mods do not match, or BattlEye and CPU performance are interrupting connections. Check those causes in that order instead of repeatedly reinstalling the game.
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The procedure below separates a server that is genuinely unreachable from one that is merely missing from the browser, then deals with Session Lost, BattlEye kicks and desynchronisation.
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First, identify what “not working” means
Different symptoms point to different layers of the setup. Use this table before changing settings.
| Symptom | Most likely area | First test |
|---|---|---|
| Server is absent from both LAN and Internet lists | Addressing, firewall, port forwarding, services or startup order | Try Direct Connect to the host’s public IPv4 address and port 2302. |
| Server appears, but joining fails immediately | Mod versions, signatures, BattlEye or a configuration error | Read the server log and compare the complete mod set on every machine. |
| Direct Connect works, but the browser is empty | Steam master-server listing delay or browser filters | Wait one or two minutes after a restart and clear restrictive filters. |
| Session Lost appears while joining | Usually a mod-version or signature mismatch | Make the server and every client use identical mod files and signatures. |
| BattlEye: client not responding appears | Usually the connecting client rather than the dedicated server | Test another client and inspect the affected client’s BattlEye state and logs. |
| Players connect but suffer severe desync | Server CPU load or mission/mod complexity | Watch CPU usage while the problem occurs and simplify the mission or mod set. |
1. Prove that the server can be reached
Confirm a real public IPv4 address
The Bohemia Interactive community wiki’s dedicated-server guidance says an Internet server needs a public IPv4 address. IPv6-only connectivity and DS-Lite tunnels are not supported for this purpose. A router address in a private range, or a connection where the provider places you behind DS-Lite, can make local testing look successful while outside players can never connect.
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Check the IPv4 address shown by the server’s Internet connection and compare it with the address visible from an external network. If the connection has no publicly routable IPv4 address, port-forwarding rules on your own router cannot make the server reachable; ask the ISP for a public IPv4 service or host the server on a network that provides one.
Make the host answer and open the required traffic
The same wiki guidance says the machine must answer ICMP echo (ping) and that the game’s TCP and UDP traffic must be allowed through the host firewall and router. Forward the game port to the computer running the dedicated server, and create matching inbound firewall rules. Apply the rule to the correct private address; a DHCP change can silently leave a forward pointing at another device.
Do not test only from another computer on the same home network. A router may allow a local connection even though the Internet-facing rule is wrong. Test from a different network, such as a mobile hotspot, or ask a remote player to try while you monitor the server.
Check Windows discovery and UPnP services
For Windows hosts, the wiki specifically notes Network Discovery, UPnP Device Host and SSDP Discovery. Open the Windows Services console, locate those entries and confirm that they are present and running when you expect the server to publish or discover network information. A disabled discovery service can make a working process appear invisible on a LAN.
UPnP can create router mappings automatically, but it is not a substitute for a public IPv4 address. If automatic mapping is unreliable, use explicit forwarding and firewall rules and treat UPnP as optional.
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2. Start the dedicated server before Steam
Bohemia Interactive’s dedicated-server instructions note that the dedicated process should be started before the Steam client. Steam-related port handling can fail when Steam is already running and the server is launched afterward.
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- Start the Arma 3 dedicated-server process and wait until its console or log shows that initialization has progressed without an immediate configuration error.
- Only then start Steam on that computer.
- From a remote machine, test Direct Connect before judging whether the public browser has updated.
If you normally start both programs through a script or a hosting panel, change the sequence there. Restarting only the game client does not correct a dedicated process that was launched after Steam.
3. Correct Steam query ports and server.cfg
Remove stale manual Steam-port lines
A low.ms hosting guide reports that Arma 3 automatically derives steamPort and steamQueryPort from the game port: the first is the game port plus one and the second is the game port plus two. With the usual game port 2302, that means 2303 and 2304. If you changed the game port, the derived values change with it.
The guide recommends removing old, manually entered steamPort and steamQueryPort lines from server.cfg rather than preserving values copied from another installation. Incorrect manual values can be worse than leaving the settings out and allowing automatic assignment. After removing them, restart the server and forward the resulting ports as required by your firewall and router.
Find a strict-parser failure
The same guide warns that the configuration parser is strict: one malformed line can stop startup or leave the server only partially initialized. This commonly follows a recent edit, a missing quote or brace, an invalid separator, or a line copied from a different configuration example.
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- Stop the dedicated server and make a backup of the current
server.cfg. - Compare the last edited lines with a known-good configuration for the same Arma 3 server build.
- Temporarily remove nonessential custom settings, especially manually assigned Steam-port entries.
- Start the server and read the first error in the console or log, not only the final shutdown message.
- Reintroduce optional settings in small groups until the offending line is identified.
A server that closes immediately, never reaches normal initialization, or produces no browser entry after a configuration change should be treated as a syntax problem until the log proves otherwise.
4. Separate a listing problem from a connection problem
Use Direct Connect to the default game port
The low.ms guide recommends Direct Connect to the server’s public IP address and port 2302 when that is the configured game port. This bypasses the public-server browser.
- Direct Connect succeeds: the network path and game process are working. The remaining issue is likely Steam listing delay, a browser filter, or a query-port problem.
- Direct Connect fails: continue with public IPv4, forwarding, firewall, startup order, configuration and mod checks. The browser is not the root cause.
Do not conclude that a restart failed merely because the server is absent immediately afterward. The low.ms guide says Steam’s master-server listing can take about one or two minutes to reflect a restart. Wait that long, then refresh the browser and remove filters for password, ping, difficulty, version and mods that could hide the entry.
Check the address and port you are actually publishing
Use the server’s current public IPv4 address, not its private LAN address, when testing from outside the network. If you deliberately changed the game port, substitute that port for 2302 and ensure the corresponding forwarding rule and derived Steam ports follow the same change.
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5. Fix Session Lost and mod/signature mismatches
The low.ms troubleshooting guide attributes many Session Lost errors to a mod-version mismatch or a failed signature check. A server and all connecting clients need the same mod versions and signatures; having a mod with the same name is not enough if one side has been updated, partially downloaded or manually replaced.
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Compare the complete installation, not just the visible list
- Record the mods enabled by the server and the exact versions currently installed there.
- Have each client compare its enabled set and installed files with that server list.
- Remove stale or duplicate copies before reinstalling the required version.
- Restart the dedicated server after correcting files so it loads the new signatures.
- Test with one client before inviting the whole group; this prevents several mismatches from producing overlapping errors.
If one player is rejected while others join successfully, focus on that client’s files and signatures first. If every client is rejected after a mod update, inspect the server’s copy and its startup parameters before changing router settings.
When a manual upload has broken the setup
A Steam Workshop discussion describes one user fixing a damaged server by reinstalling it and subscribing to the required mods through the in-browser Workshop. That is an anecdotal report, not a guaranteed repair, but it suggests a useful recovery when manually uploaded files are incomplete or out of sync: remove the suspect installation, reinstall cleanly, obtain the same Workshop content on the server and clients, and retest before adding custom files.
When no mission loads
One Steam discussion reports that adding the autoinit startup parameter helped when the server had no mission loaded. This is a community suggestion rather than a universal requirement. Consider it only after reachability and configuration are working, and confirm in the log that a mission actually initializes. Do not use autoinit to mask a failed network or mod setup.
6. Handle BattlEye kicks on the client side first
A BattlEye kick reading BattlEye: client not responding is often a client-side problem, according to the low.ms guide. Before rebuilding the dedicated server, check whether another player can join. A successful connection from a second client strongly shifts the investigation to the rejected computer.
- Have the affected player restart the game and reconnect after the server has fully initialized.
- Inspect that client’s BattlEye messages and logs for a timeout or failed startup.
- Confirm the client is connecting to the same server version and mod/signature set as everyone else.
- Temporarily compare behavior on another network or computer to distinguish a local client problem from a server-wide failure.
If every client receives the same BattlEye message, return to the server log and startup sequence. A server that never completes initialization can cause clients to time out, but one isolated kick is not evidence that the host is broken.
7. Reduce CPU pressure when players desynchronise
The low.ms guide says many Arma 3 desynchronisation problems are CPU-bound rather than bandwidth-bound. A fast Internet connection cannot compensate for a server thread that is overloaded by a complex mission or a large mod set.
Measure during the failure
Watch the dedicated host’s CPU load while players report desync. Note whether the load rises when a particular mission starts, when many AI units spawn, or when a scripted event runs. Compare a simple mission with the usual mission; the comparison is more useful than an idle CPU reading.
Reduce the workload methodically
- Remove nonessential mods and test again.
- Use a less complex mission or reduce its active AI and scripted activity.
- Change one major factor at a time so you can identify what relieved the load.
- Keep the smallest stable mod and mission combination as a recovery profile.
Do not automatically purchase more bandwidth or blame a player’s connection when the server CPU is saturated. If CPU load remains normal and only one player desynchronises, investigate that player’s client and route separately.
Dedicated server versus listen-server advice
A 2021 Steam thread suggested forwarding UDP ports 2302 through 2306 and enabling UPnP. The discussion concerned listen servers, and the exact thread details were not confirmed, so it should not be treated as a general dedicated-server rule. Dedicated servers should follow the game-port and automatically derived Steam-port behavior described above, then verify the result with Direct Connect and the server log.
A clean recovery sequence
Use this order after a failed setup or a major configuration change. It minimizes the chance of fixing one layer while another remains broken.
Quick Recap
- Network: verify a public IPv4 address, confirm the host answers ping, and check inbound TCP/UDP firewall and router rules.
- Windows services: confirm Network Discovery, UPnP Device Host and SSDP Discovery are available and running when needed.
- Configuration: back up
server.cfg, remove manually assignedsteamPortandsteamQueryPortlines, and correct any parser error. - Startup: exit Steam, launch the dedicated server first, wait for initialization, then start Steam.
- Connection: Direct Connect to the public IP and port 2302, or to your changed game port.
- Listing: if Direct Connect works, wait one or two minutes, refresh the browser and remove filters.
- Content: align mod versions and signatures on the server and every client; read logs for the first rejection.
- Security: investigate an isolated BattlEye: client not responding kick on that client before rebuilding the host.
- Performance: if connections succeed but desync persists, measure CPU load and simplify the mod or mission workload.
Common mistakes that waste time
- Forwarding ports on a router that has no public IPv4 address.
- Changing several firewall and configuration values before trying Direct Connect.
- Leaving copied manual Steam-port lines in
server.cfgafter changing the game port. - Assuming a missing browser entry means the server is unreachable without waiting for listing propagation.
- Comparing only mod names instead of versions, signatures and actual installed files.
- Blaming the host for one BattlEye client timeout when other players can join.
- Adding more bandwidth when the dedicated process is CPU-bound.
- Applying listen-server port advice unchanged to a dedicated server.
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