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Troubleshooting

Running into issues with your server or client? This guide covers common problems and their solutions.

Server Connection Issues​

"Failed to connect to server. Are you sure it is up?"​

If you're experiencing this error message, it's usually related to firewall or port configuration issues.

Solution:

Make sure that both ports are open in your firewall:

  • Port 7777 (or whatever port you set in your config as the port field)
  • Port 7778 (or your configured port + 1)

The server uses two ports:

  • The main port (default 7777) for player connections
  • Port + 1 (default 7778) for the HTTP server that serves server information and mods

To check if your ports are open:

  1. Windows Firewall:

    • Open Windows Defender Firewall
    • Click "Advanced settings"
    • Create inbound rules for both TCP ports (your port and port+1)

  2. Linux (iptables/ufw):

    # For ufw
    sudo ufw allow 7777/tcp
    sudo ufw allow 7778/tcp

    # For iptables
    sudo iptables -A INPUT -p tcp --dport 7777 -j ACCEPT
    sudo iptables -A INPUT -p tcp --dport 7778 -j ACCEPT

  3. Router/Network Configuration:

    • If you're hosting from home, make sure your router forwards both ports to your server's local IP address
    • Check that your ISP isn't blocking these ports

  4. Cloud Hosting:

    • Verify that your cloud provider's security groups/firewall rules allow both ports
    • Some providers require you to explicitly open ports in their control panel
Port Configuration

If you've changed your server's port in config.json, remember to open both the new port AND port+1. For example, if your server uses port 8888, you'll need to open ports 8888 and 8889.

"Invalid address. IPv6 is not supported"​

If you see this error message, it means your machine is using IPv6, but JC4MP servers require IPv4 connectivity. You'll need to configure your system or network to use IPv4.

Solution:

JC4MP servers only support IPv4 addresses. Here are common ways to resolve this issue:

For Linux Cloud Hosting​

If you're hosting on a cloud provider (AWS, DigitalOcean, Linode, etc.):

Reserve a Public IPv4 Address

  • Most cloud providers assign IPv6 by default or require you to explicitly request an IPv4 address
  • In your cloud provider's control panel, look for networking settings
  • Request or allocate a public IPv4 address for your server instance
  • Make sure your server is binding to the IPv4 address (usually 0.0.0.0 or your specific IPv4 address)

For Home/Residential Setup​

If you're hosting from home:

  1. Check Router Settings

    • Log into your router's admin panel (usually 192.168.1.1 or 192.168.0.1)
    • Look for IPv6 settings and disable IPv6 if it's causing issues
    • Ensure your router is forwarding IPv4 traffic properly

  2. Update Port Forwarding

    • Make sure your router's port forwarding rules are configured for IPv4
    • Verify that your server's local IPv4 address is being used (not IPv6)

  3. ISP Configuration

    • Some ISPs may provide IPv6-only connections
    • Contact your ISP to request IPv4 connectivity or a dual-stack connection
    • You may need to request a static IPv4 address

For Windows Servers​

  1. Disable IPv6 (if needed)

    • Open Network and Sharing Center
    • Go to your network adapter properties
    • Uncheck "Internet Protocol Version 6 (TCP/IPv6)"
    • Restart your network adapter

  2. Verify IPv4 Binding

    • Ensure your server is binding to IPv4 addresses (check your server configuration)

Testing Your Configuration​

To verify you're using IPv4:

# Check your IP address (should show IPv4)
ip addr show    # Linux
ipconfig        # Windows

# Test connectivity using IPv4
ping -4 google.com    # Linux
ping -4 google.com    # Windows (PowerShell)
IPv6 Support

JC4MP currently only supports IPv4. If you're on an IPv6-only network, you'll need to configure IPv4 connectivity or use a tunnel service that provides IPv4 access.

Other Common Issues​

Server Not Appearing in Server List​

If your server isn't showing up in the JC4MP server list:

  1. Check your announce field - Make sure it's set to true in your config.json
  2. Verify your server key - Ensure you have a valid key from the JC4MP Server Dashboard
  3. Check your update_url - Should be set to https://servers.jc4mp.com/api/v1/servers
  4. Wait a few moments - Server list updates may take a few moments to propagate

Version Mismatch Errors​

If players can't connect and see version mismatch errors:

  • Server version must match client version exactly
  • Make sure both your server and clients are using the latest version
  • Check the Servers page to ensure you have the latest server build

Authentication Issues​

If players are having trouble authenticating:

  1. Verify your Steam Web API Key - Make sure your steam_web_api_key in config.json is valid
  2. Check Steam API Status - Visit Steam's API status page to ensure Steam services are operational
  3. Regenerate your API key - If issues persist, try generating a new Steam Web API key from Steam's Web API Key page

Connecting Directly via IP​

If your server isn't appearing in the server list, or if you want to connect quickly, you can connect directly using the IP address:

How to connect:

  1. Open the JC4MP launcher
  2. Type the server's IP address at the top of the launcher (include the port if not using default 7777, e.g., 192.168.1.100:7777)
  3. Press Enter to connect

For local servers: If you're hosting locally at home and want to connect from the same machine:

  • Use localhost (or 127.0.0.1) to connect to your local server
  • Or find your local IP address:
    • Windows: Open Command Prompt and run ipconfig - look for "IPv4 Address" under your network adapter
    • Linux/Mac: Open Terminal and run ifconfig or ip addr show - look for your local IP (usually starts with 192.168. or 10.)

Example: If your local IP is 192.168.1.100, type 192.168.1.100:7777 in the launcher to connect.

Need more help? Check out our other guides or visit the JC4MP Discord for community support!