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Players try the direct path first. If that path is unavailable, the game falls back to Steam, but the official warning says a closed direct port can severely affect performance. A successful Steam listing therefore does not prove that the server’s preferred connection path is working.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsDefault Project Zomboid ports at a glance
| Port | Protocol | Default role | Forwarding requirement |
|---|---|---|---|
| 16261 | UDP | Game port used for Steam queries | Forward the configured value to the server computer when players connect from outside your network. |
| 16262 | UDP | Additional port used for the direct client connection | Forward the configured value as well; this is the preferred path for direct traffic. |
These are defaults, not permanent assignments. The server options can change either value. Your running server’s generated .ini file or startup output is authoritative; router rules, host-firewall rules, container mappings and hosting-panel settings must all use those active values.
What each port does
UDP 16261: game and Steam-query traffic
The default game port is UDP 16261. It handles Steam queries, which helps the game and Steam determine that the server is available and obtain its connection information. A forwarding rule for this port is necessary when remote players need to discover or reach a server behind your router.
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UDP 16262: the direct connection
The additional default port is UDP 16262. It carries the direct client connection that Project Zomboid prefers when a player joins. Direct UDP traffic normally avoids the extra dependency of a relay or fallback path, so this port should not be treated as optional simply because the server appears in a list.
How Project Zomboid chooses a connection path
- Direct attempt: the client first tries to reach the server through the direct port, normally UDP 16262.
- Fallback attempt: if the direct path fails, the client tries to connect through Steam, using the game/query arrangement associated with UDP 16261.
- Warning and degraded behavior: when the direct port is unreachable, the client can display
WARNING: SERVER HAS PORT %1 CLOSED. PERFORMANCE MAY BE SEVERELY AFFECTED. The server may still be joinable through Steam, but that does not restore the preferred direct route.
A listing that appears in Steam is therefore only a partial test. For consistent performance, make both UDP paths reachable from the internet.
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Check the generated server configuration
After the dedicated server has started at least once, open the generated server .ini file and identify the configured game port and additional port. File names and locations depend on the installation method, so use the configuration directory created by your server rather than assuming that the defaults are still active.
Check startup output
Server startup output can also show the listening values. Compare those values with the entries in the .ini file. If they disagree, stop the server, correct the configuration that the launcher actually reads, and start it again before changing your router.
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Treat custom values as a complete set
If you changed either port, update every place that refers to it:
- Router or gateway port-forwarding rules.
- Windows, Linux or other host-firewall rules.
- Container publish mappings, if the server runs in a container.
- Managed-hosting control-panel mappings.
- Saved server entries on every player’s client.
Do not assume that changing the first port automatically changes the second. Read both active values and map both explicitly.
Forward both UDP ports on a home router
The labels differ by router manufacturer, but the required information is the same: protocol UDP, the server computer’s local IP address, and the two active port numbers.
- Give the server a stable local address. Create a DHCP reservation for the server computer or configure a static address. A forwarding rule aimed at a changing address will eventually point to the wrong device.
- Open the router administration page. Look for Port Forwarding, NAT, Virtual Server or a similarly named section.
- Create the game-port rule. Set the protocol to UDP, enter the active game port (16261 by default) as the external and internal port, and select the server computer’s local IP address.
- Create the direct-port rule. Add a second UDP rule for the active additional port (16262 by default), again pointing to the same local IP address.
- Save and apply. Some routers require an apply action or restart before the rules become active. Avoid creating TCP-only rules; the documented defaults are UDP.
- Check for duplicate or stale entries. Remove old rules that point to a previous computer or obsolete custom port, especially if you experimented with UPnP.
- Restart or reload the server if necessary. Confirm from its startup output that it is listening on the same values you entered in the router.
- Test from outside the LAN. Have a player on a different internet connection join. A test from the same home network can succeed through local routing even when internet forwarding is broken.
If remote connections fail even though the rules and firewall are correct, determine whether your internet service uses carrier-grade NAT. With carrier-grade NAT, the router may not receive a publicly reachable address, so ordinary inbound forwarding cannot work; your internet provider or network administrator must supply a reachable address or an alternative arrangement.
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Allow the ports through the server computer’s firewall
Port forwarding only moves packets to the host. The operating system must also permit unsolicited UDP traffic on both active ports.
Windows Defender Firewall
- Open Windows Defender Firewall with Advanced Security.
- Select Inbound Rules, then New Rule.
- Choose Port, select UDP, and enter the game port, 16261 by default.
- Choose Allow the connection, apply the rule to the profiles that the server uses, and give it a descriptive name.
- Repeat the process for UDP 16262, or for both active custom values.
Administrators who prefer PowerShell can create equivalent rules (run an elevated shell):
New-NetFirewallRule -DisplayName 'Project Zomboid UDP 16261' -Direction Inbound -Protocol UDP -LocalPort 16261 -Action Allow
New-NetFirewallRule -DisplayName 'Project Zomboid UDP 16262' -Direction Inbound -Protocol UDP -LocalPort 16262 -Action AllowReplace the numbers when the server configuration uses custom ports.
Linux with UFW
On a host using UFW, allow each UDP port and then verify the rules:
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sudo ufw allow 16261/udp
sudo ufw allow 16262/udp
sudo ufw statusOn systems using another firewall manager, create equivalent inbound UDP rules there. Opening a port in UFW does not override a separate cloud, hypervisor or security appliance policy.
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Check locally first
Use the operating system’s socket or process tools to confirm that the dedicated server is running and bound to the expected UDP ports. If no process is listening, a router rule cannot fix the problem; inspect the server startup output and configuration first.
Perform a real remote join test
Have a player outside your local network use the server’s public address and the configured port. Watch the client for the closed-port warning and watch the server console for an incoming connection. UDP port-check websites often produce inconclusive results because UDP services may not answer a generic probe; an actual Project Zomboid join is the meaningful test.
Test after every change
Change one layer at a time—server configuration, firewall, router or client entry—then test again. This prevents a successful result from hiding which rule was actually required and makes rollback easier.
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UPnP: automatic forwarding is not automatic verification
Project Zomboid’s newer port arrangement includes UPnP changes intended to create the needed forwarding rules automatically when the router supports working UPnP. Automatic creation is convenient, but it is not proof that the correct rules exist. UPnP may be disabled, unsupported, blocked by another network device or pointed at an old local address.
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- Check the router’s UPnP table for both UDP ports.
- Confirm that the destination address is the current server computer.
- Compare the listed numbers with the server’s active configuration.
- Remove stale mappings and resolve conflicts with manually created rules.
- If automatic rules are unreliable, create explicit manual UDP forwards and retest.
Troubleshoot by symptom
| Symptom | Likely cause | What to check |
|---|---|---|
| Players on the same LAN can join, but internet players cannot. | Router forwarding, public-address or host-firewall problem. | Stable local IP, two UDP forwards, operating-system firewall and possible carrier-grade NAT. |
| The server appears in Steam, but the client reports the direct port closed. | UDP 16262, or its custom replacement, is blocked or mapped to the wrong host. | Direct-port router rule, host-firewall rule and listening output. |
| The client shows the severe-performance warning. | The preferred direct path could not be reached. | Open the configured additional port and test from a genuinely external connection. |
| A port scanner says the UDP port is closed while a player can join. | Generic UDP probes may not understand the game protocol. | Use a real remote join and server logs as the deciding test. |
| Connections stopped after changing ports. | One layer still uses the previous values. | Reconcile the .ini, startup output, router, firewall, container or panel mapping and saved client entry. |
| UPnP created rules that do not work. | UPnP is disabled, stale or targeting a different local address. | Inspect the router table, delete stale entries and add explicit forwards if needed. |
| A containerized server is unreachable. | The host ports were not published to the container, or the protocol was set to TCP. | Publish both active ports as UDP and verify the container’s internal listening values. |
Running more than one server or changing defaults
Every server instance needs a distinct reachable port assignment. When you add another instance, choose unused values in its configuration and create matching UDP mappings to the correct machine or container. Never send one external port to two different destinations; the router cannot decide which server should receive the packet.
Players who saved the old address and port must edit their server entry or create a new one. A server can be healthy while an individual client continues trying the obsolete value.
Self-hosting versus managed hosting
The port requirements remain the same, but responsibility changes depending on where the server runs.
| Consideration | Self-hosted server | Managed hosting |
|---|---|---|
Control over .ini and firewall settings |
Full control; you edit the file and operating-system rules directly. | Often mediated by a control panel; available settings depend on the host. |
| Ability to forward UDP ports | You configure the home or office router and host firewall. | The provider normally supplies the public mapping; verify both UDP values in the panel. |
| Setup effort | Higher: install, configure, forward, secure and maintain the machine. | Lower initial network work, but you still need to configure the game and test access. |
| Direct-connection reliability | Depends on your router, public address, firewall and upload connection. | Depends on the provider’s network and whether the assigned ports are reachable. |
| Ongoing maintenance | You handle updates, backups, operating-system patches and troubleshooting. | The provider may handle infrastructure, while you remain responsible for game settings and access testing. |
Whichever model you choose, verify the actual listening ports rather than relying on a generic defaults list. A panel that displays a public port can still be forwarding to the wrong internal value, and a self-hosted server can still be blocked by an upstream network.
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Final setup checklist
- Read both active UDP values from the server configuration or startup output.
- Forward the game port, UDP 16261 by default, to the server host.
- Forward the additional direct port, UDP 16262 by default, to the same host.
- Allow both values through the operating-system firewall.
- Verify UPnP-created rules or replace them with explicit mappings.
- Update container, hosting-panel and saved-client settings when values change.
- Test with a player outside the local network and investigate any direct-port warning.
The practical answer is simple: forward UDP 16261 and UDP 16262 for a default installation, but trust the ports shown by the running server whenever they differ. The first supports Steam queries, the second provides the preferred direct connection, and both must agree across the server, router, firewall and client.
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