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If Arma Reforger reports Server Unreachable, the game is usually running but clients cannot reach its UDP endpoint. Start with the documented ports, then verify the server’s registered address, host firewall, router forwarding and NAT type. The fastest isolation test is to join the server from the same LAN by its private IP; that separates a local configuration fault from an Internet-routing problem.
What the error means
Arma Reforger uses a dedicated server socket and a backend registration entry. A client must reach the game’s UDP port, while the server browser uses a separate query port to discover and display the instance. A failure at either stage can look like the same symptom: the server is absent from the browser, appears briefly and then disappears, or produces Group 1 Replication reason=11 Server Unreachable after a connection attempt.
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This is a connectivity problem, not a missing-content or purchase problem. Mods, maps and player permissions matter only after a client can establish the network session. Fix the network path first.
Use the correct default ports
Unless you deliberately changed them, use these documented defaults:
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| Purpose | Protocol | Default port | Where it must be allowed |
|---|---|---|---|
| Game host socket | UDP | 2001 | Server process, operating-system firewall and router/NAT rule |
| Steam/A2S server-browser query | UDP | 17777 | Server process, operating-system firewall and router/NAT rule when browser visibility is required |
| RCON remote administration | UDP | 19999 | Only when RCON is enabled and remote administration is needed |
Port 2001 carries game traffic. Port 17777 is for server-browser queries, so forgetting it can leave a healthy server invisible even though a direct connection works. Port 19999 is optional; do not expose it merely because a hosting guide lists it. Keep RCON closed when you do not use it.
The official defaults are UDP. Documentation and community guides disagree about whether a TCP 2001 rule is useful. Treat UDP as the supported baseline and do not add broad TCP forwarding unless a specific, current server or network requirement tells you to.
Check the server configuration before changing the network
The backend advertises the address and port values in the server configuration. A typo, stale public address or mismatched port can make a correctly forwarded server unreachable.
| Field | Function | Default or documented behavior | What to do |
|---|---|---|---|
bindAddress |
Local interface to which the UDP socket binds | 0.0.0.0 when omitted |
Usually omit it so the server listens on all IPv4 interfaces. |
bindPort |
Local UDP socket port | 2001; valid range 1–65535 | Generally omit it so it follows publicPort. |
publicAddress |
Public address registered for clients | Automatically detected when missing or empty | Leave empty unless automatic detection publishes the wrong address. |
publicPort |
UDP port registered in the backend | 2001 | Make it match the externally forwarded game port. |
IPv6 is not supported for this server path. Use an IPv4 address. If your machine has several network adapters, a VPN, a virtual switch or both Wi‑Fi and Ethernet, an explicitly entered address can easily point clients to the wrong interface.
Use current field names
Build 0.9.8.73 renamed two settings. Replace gameHostBindPort with bindPort, and replace gameHostRegisterBindAddress with publicAddress. Guides that still show the old names are written for an earlier build and can lead you to edit settings the current server no longer reads.
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When to set a public address manually
Start with publicAddress absent or empty. The backend then detects the address. Set it only when the server registers a private address, an obsolete ISP address or another unreachable interface. Enter the host’s current public IPv4 address, not its LAN address such as 192.168.x.x, 10.x.x.x or 172.16–31.x.x. If your ISP changes the public address, update the setting or return to automatic detection.
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Fix the host firewall
Port forwarding on the router cannot bypass a firewall on the server computer. Create inbound UDP allowances for every port you actually use.
- Stop the dedicated server.
- Open Windows Security, choose Firewall & network protection, then Advanced settings.
- Select Inbound Rules and create a new Port rule.
- Choose UDP, enter the game port (normally
2001), allow the connection, and apply it to the network profiles that describe your host. - Create a second UDP rule for
17777if you need server-browser visibility. - Create a UDP rule for
19999only when RCON is enabled and must be reachable remotely. - If you previously blocked the game executable or BattlEye, inspect existing rules and remove the block or add a narrowly scoped allow rule.
- Restart the server and confirm that the rules remain enabled.
Some third-party firewall products silently place the game or BattlEye back on a blocked list after an update. Check the product’s blocked-app and quarantine views, not only the Windows rules. Avoid downloading or running PowerShell “fix” scripts posted in forums; inspect and create the rules yourself.
Forward the ports on the router
Router forwarding maps an Internet-facing UDP port to the host’s private IPv4 address. The destination must be the computer running the Reforger server, not the router and not another machine that happens to run the game client.
- Give the server computer a DHCP reservation or static LAN address so it does not change after a reboot.
- Sign in to the router and open Port Forwarding, NAT or Virtual Server.
- Add a UDP rule for external port
2001to the host’s private IP and internal port2001. - Add UDP
17777to the same host if browser discovery is required. - Add UDP
19999only for remote RCON administration; restrict its source addresses when the router supports that option. - Save the rules, apply the router configuration and restart the server process.
Keep external and internal ports identical unless you have a reason to translate them. If you choose a different external game port, set publicPort to that value and ensure the server’s bind setting follows it. A mismatch between the forwarded port and the value registered in the backend produces an unreachable listing.
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Test from inside the same network
Many consumer routers do not support NAT hairpinning (also called NAT loopback). That means a device inside your home network may fail when it tries to reach your public IP even though players on the Internet can connect. Do not treat that single test as proof that forwarding is broken.
- Find the server computer’s private IPv4 address in the operating system’s network details.
- From another device on the same LAN, use the game’s direct-connect option or server list and target that private address.
- If the LAN connection succeeds, the server process, local firewall and game port are probably working. Concentrate on the router’s WAN rule, public address and ISP NAT.
- If the LAN connection fails, inspect the server process, bind settings and host firewall before changing the router.
Do not use the public address for this test. A successful LAN test and a failed public test indicate two different classes of problem; keeping them separate prevents unnecessary configuration changes.
Determine whether your ISP uses CGNAT
Carrier-grade NAT (CGNAT) places another translation layer between your router and the Internet. In that arrangement, your router may show a WAN address that differs from the public IPv4 address visible to outside services. Port forwarding on your own router cannot accept unsolicited traffic through the ISP’s upstream NAT.
- Compare the router’s WAN IPv4 address with the public IPv4 address reported by a trusted network-information service.
- If they differ, or the router WAN address is in a private or shared range, ask the ISP whether the connection uses CGNAT.
- Request a public IPv4 address or a suitable static address if the ISP offers one. IPv6 is not a workaround here because the documented server path does not support IPv6.
When CGNAT is confirmed and the ISP cannot provide a public IPv4 address, no local port-forwarding combination will make the server directly reachable from the Internet. Use a network service that supplies a public endpoint or host the server on a connection without that restriction.
Check the address and port that the backend registered
A server can be running and listening locally while advertising an address clients cannot use. Look at the server configuration and startup output for the registered public address and port.
- Confirm that the registered address is the host’s current public IPv4 address, or remove
publicAddressand let the backend detect it. - Confirm that
publicPortis the same UDP port forwarded on the router. - Confirm that
bindPortis omitted or matches the intended port. The documented recommendation is generally to omit it so it automatically usespublicPort. - Remove obsolete field names from older guides and replace them with
bindPortandpublicAddress.
If the public address changes frequently, a previously working configuration can fail without any game update. Recheck the address after an ISP reconnect, router replacement or VPN installation.
Separate browser visibility from direct connectivity
There are two related but distinct symptoms:
The server is absent from the browser
First verify UDP 17777 through the host firewall and router. Then verify that the server has registered the intended public address and port. A missing query rule can hide an otherwise reachable server.
The server appears, but joining ends with Server Unreachable
Focus on UDP 2001, the registered game port and the destination private IP in the forwarding rule. A browser listing proves that a query response was seen; it does not prove that the game socket is reachable.
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The server process is likely healthy. Recheck the WAN forwarding rule, CGNAT status, public address and any upstream firewall supplied by the ISP or a second router.
Both LAN and Internet connections fail
Check that the dedicated server is actually running, that it is listening on the expected port, that the current configuration uses supported field names and that the host firewall allows UDP traffic.
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RCON is optional and should be isolated
RCON is a remote-administration channel, not a requirement for ordinary gameplay or browser discovery. The documented default is UDP 19999. If you do not administer the server remotely, leave that port closed. If you do use RCON, forward only UDP 19999, protect it with a strong credential and limit source addresses where possible. A custom convention that calculates RCON from the game port is not the game’s default; verify the actual configuration before opening any additional port.
What to do about TCP rules
One guide may recommend a TCP 2001 firewall rule while another says Reforger uses UDP exclusively. The official default-port information identifies UDP for the game and query paths but does not establish a general TCP requirement. Begin with UDP only. If a current server log or a specific network appliance documents a TCP dependency, add the narrowest rule necessary and test it independently; do not forward an entire range or enable both protocols as a blind fix.
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- Process: Is the dedicated server running continuously, without a crash or immediate shutdown?
- Configuration: Are
bindPortandpublicAddressthe current names, and do the values match the intended public endpoint? - Local reachability: Can another LAN device connect to the host’s private IP?
- Firewall: Are inbound UDP 2001 and, when needed, UDP 17777 allowed on the host?
- Router: Do the forwarding rules target the correct private IP and remain present after reboot?
- ISP path: Is the router receiving a real public IPv4 address rather than CGNAT?
- Backend: Do multiple clients fail after all local checks pass, or do server listings show inconsistent registration?
This order prevents a common mistake: changing backend fields when the host firewall is blocking traffic, or changing router settings when the server is bound to the wrong port.
Backend outages and intermittent failures
Occasionally, players report backend errors even when their local configuration is correct. If the server passes the LAN test, the UDP rules are correct, the public address is valid, CGNAT is not present and several unrelated clients fail at the same time, the remaining cause may be an official backend incident. Check the game’s current official service notices and retry after the incident is resolved. Do not delete a working configuration or rotate ports repeatedly while the backend is unavailable.
Common mistakes that waste time
- Forwarding TCP only and leaving UDP 2001 closed.
- Opening 2001 but forgetting UDP 17777, then assuming the server process is broken because it is absent from the browser.
- Entering a private LAN address in
publicAddress. - Setting
bindPortto one value while forwarding and registering another. - Following a pre-build-0.9.8.73 guide that uses renamed fields.
- Testing the public IP from inside a router that lacks NAT hairpinning.
- Forwarding to a DHCP address that changed after a reboot.
- Opening RCON even though nobody needs remote administration.
- Trusting an online port checker as the only evidence. UDP checkers can report failure even when a service is reachable, so use an actual LAN and external game-connection test.
- Running an unknown forum PowerShell script that changes firewall policy globally.
A clean rebuild procedure
If the configuration has accumulated conflicting entries, use this controlled reset rather than editing random values:
- Record the server’s current private IPv4 address and stop the server.
- Back up the configuration, then remove obsolete fields and retain current names.
- Leave
bindAddress,bindPortandpublicAddressabsent or empty unless a specific problem requires them. - Set
publicPortto 2001, or to one deliberate custom UDP port that you will use consistently. - Create only the required host-firewall rules: UDP 2001 and, for discovery, UDP 17777.
- Reserve the private IP in DHCP and create matching router-forwarding rules.
- Start the server and perform a LAN private-IP test.
- After LAN success, test from a genuinely external connection, such as a friend’s network or a mobile connection that is not on the same Wi‑Fi.
- Add RCON only after gameplay connectivity works.
Changing one layer at a time leaves a clear cause-and-effect trail. If the LAN test fails, stop there; Internet testing cannot repair a local bind or firewall problem.
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Contact the ISP when the router is behind CGNAT, the WAN address is not publicly routable or upstream filtering is suspected. Contact game support with the build number, the exact error text, whether LAN direct connection works, the configured public and bind ports, and whether independent external clients fail. Do not include RCON credentials or expose a private address unnecessarily.
For most installations, the fix is straightforward: allow UDP 2001 on the host and router, allow UDP 17777 for browser queries, keep the current configuration field names, register a reachable IPv4 address and verify the path with a LAN test before troubleshooting the Internet side.
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