How to Fix the Connection Refused Error on the MU Online ConnectServer

The "connection refused" error when trying to log into the server is, by far, the most commonly reported problem among MU Online private server admins — and also the most poorly diagnosed, because the message on the client is generic and doesn't say whether the problem lies in the process, the firewall, the router, or the configuration the player typed in. This tutorial walks through the entire path of the packet, from the client's login screen to the ConnectServer process, isolating each layer where the connection can fail. By the end, you'll know how to test each step in isolation and fix the real cause, instead of blindly restarting the server.

How the connection from client to server works

The MU Online client follows a two-step flow. First, it connects to the ConnectServer (usually TCP port 44405) using the IP configured in the IGCN.ini file or main.exe/registry, depending on the launcher version. The ConnectServer responds with the list of available servers, and when the player picks one, it returns the IP and port of the corresponding GameServer (typically 55901, 55902, etc., one per server). The client then opens a second connection, this time directly to the GameServer. If either of these two ends is blocked or misconfigured, the player sees "connection refused" or gets stuck on the server selection screen.

Typical symptoms and what each one indicates

Step 1 — Confirm the processes are running

Before touching anything network-related, confirm that ConnectServer.exe, JoinServer.exe, and GameServer.exe (names vary by emulator: IGCN, MuEMU, X-Team) are actually running without errors in the console. A ConnectServer that silently crashes on boot is cause number one of this error, and it's easy to mistake for a network issue.

Get-Process | Where-Object { $_.ProcessName -match "ConnectServer|GameServer|JoinServer" }

If the process doesn't show up, open the executable manually from the console and read the error message — it's usually a failed database connection (DataServer/MySQL) or the port already being used by another process.

Step 2 — Test the port locally

With the processes running, test whether the port responds on the server machine itself:

Test-NetConnection -ComputerName 127.0.0.1 -Port 44405
Test-NetConnection -ComputerName 127.0.0.1 -Port 55901

If TcpTestSucceeded returns False even locally, the problem isn't external networking — it's that the process isn't listening on that port (check the ConnectServer's configuration file, usually ServerList.dat or ConnectServerInfo.dat, where the port is defined).

Step 3 — Open the port in Windows Firewall

If the local test worked but it fails from outside, the next suspect is Windows Firewall. Create explicit inbound rules for TCP and UDP on the ConnectServer and GameServer ports:

New-NetFirewallRule -DisplayName "MU ConnectServer TCP" -Direction Inbound -Protocol TCP -LocalPort 44405 -Action Allow
New-NetFirewallRule -DisplayName "MU GameServer TCP" -Direction Inbound -Protocol TCP -LocalPort 55901-55910 -Action Allow

Port range rules (55901-55910) cover multiple GameServers without needing to create a rule for each one.

Step 4 — Check third-party antivirus and firewalls

Software like Avast, Kaspersky, and Norton maintain their own firewall, separate from Windows, and often block inbound traffic by default on ports not used by "known" applications. Add explicit exceptions for ConnectServer.exe and GameServer.exe in these programs' network/firewall settings, or temporarily disable their firewall module to isolate the test.

Step 5 — Configure port forwarding (NAT) on the router

If the server is behind a home router or an ISP NAT, you need to configure port forwarding pointing port 44405 and the GameServer range to the server machine's local IP. Without this, the external packet never reaches Windows, even with the system firewall fully open.

Step 6 — Detect CGNAT (Carrier-Grade NAT)

Some residential ISPs don't hand out a real public IP, but rather a shared one (CGNAT) — in this case, no port forwarding on the router will fix anything, because the block happens one level up, in the provider's infrastructure. To confirm, compare the IP shown in the router panel (WAN) with the public IP returned by an external service; if they differ, you're behind CGNAT and need a VPN with a dedicated IP, a VPS server, or to contact your provider for a public IP.

Step 7 — Fix the IP configuration on the client

The client file (IGCN.ini, ServerInfo.dat, or the equivalent launcher configuration) needs to point to the correct external IP of the server — not 127.0.0.1 and not a local internal-network IP, unless the player is on the same network. A common mistake is distributing the client with the server owner's local IP, which only works for that person.

[Server]
IP = 203.0.113.10
Port = 44405

Step 8 — Test with an external tool

After all adjustments, validate from outside your network using an open-port test service (for example, an online "port checker") pointed at the public IP and port 44405. If the external test confirms the port is open but the game still fails, the problem has gone back to being a client or ConnectServer configuration issue, not networking.

Common errors and fixes

Diagnostic checklist

• ConnectServer/JoinServer/GameServer processes confirmed running.
• Port successfully tested locally (Test-NetConnection).
• Windows Firewall rule created for TCP/UDP on the right ports.
• Exception added in third-party antivirus/firewall.
• Port forwarding configured on the router to the correct local IP.
• CGNAT ruled out (router IP matches public IP).
• Client configured with the server's correct external IP.
• External open-port test confirmed before launch.

Once you've eliminated the connection refused error, it's worth reviewing your project's full network architecture to prevent recurrences — especially if you're migrating from a home environment to a dedicated provider. See the MU Online server setup tutorial for a complete view of the recommended infrastructure.

Frequently asked questions