Learn how to fix “Nginx Error 99: Cannot assign requested address”. Our Nginx Support team is here to help you with your questions and concerns.

Nginx Error 99: Cannot assign requested address” | Fix

Many of our customers have had trouble with the following error message:

nginx: [emerg] bind() to IP failed (99: Cannot assign requested address)

According to our Experts, it is a common issue when starting or restarting Nginx. This error indicates that Nginx cannot bind to the specified IP address, often due to configuration or network-related issues.

Today, we are going to explore the causes, impacts, and solutions for this error, along with tips to prevent it in the future.

In short, the error means that Nginx is trying to bind to an IP address that is either incorrect, not assigned to a network interface, or unavailable for use.

An Overview:

• Impacts of the Error
• Common Causes and Fixes
• 1. Incorrect IP Address Configuration
• 2. Network Interface Not Up
• 3. Binding to a Non-Local Address
• 4. Port Already in Use
• 5. Firewall Rules Blocking Access
• 6. Misconfigured DNS Settings
• 7. IPv6 Issues When Disabled
• Preventing Future Errors

Impacts of the Error

• Nginx fails to start, resulting in downtime for websites or applications relying on it.
• Users experience errors while trying to access hosted sites.
• Requests intended for Nginx may redirect to other services, causing them to overload.
• Persistent errors can fill up log files, complicating troubleshooting.

Common Causes and Fixes

1. Incorrect IP Address Configuration

The IP address specified in the Nginx configuration does not exist on any network interface.

Fix:

• Verify the server’s IP addresses:

  ip addr show
• Update the listen directive in the Nginx configuration:

  listen <valid_IP>:<PORT<;
• Test and restart Nginx:

  sudo nginx -t
sudo systemctl restart nginx

2. Network Interface Not Up

The network interface associated with the IP address is down.

Fix:

• Check interface status:

  ip link show
• Bring the interface up:

  sudo ip link set <interface> up

3. Binding to a Non-Local Address

Nginx may be trying to bind to an IP address not local to the server.

Fix:

• Enable binding to non-local addresses in /etc/sysctl.conf:

  net.ipv4.ip_nonlocal_bind = 1
• Then, apply changes:

  sudo sysctl -p

4. Port Already in Use

Another process is using the same port Nginx is trying to bind to.

Fix:

• Identify the conflicting process:

  sudo netstat -tuln | grep :<PORT>
• Terminate the process or change the port in Nginx.

5. Firewall Rules Blocking Access

Firewall settings may block the specified IP or port.

Fix:

• Check firewall rules:

  sudo ufw status verbose
• Allow the port:

  sudo ufw allow <PORT>

6. Misconfigured DNS Settings

If a domain name resolves incorrectly to an invalid IP, Nginx will fail to bind.

Fix:

• Verify DNS resolution:

  nslookup <your_domain>
• Correct DNS records with your provider if needed.

7. IPv6 Issues When Disabled

Nginx tries to bind to an IPv6 address when IPv6 is disabled.

Fix:

Modify the configuration to listen only on IPv4:

listen <IP>:<PORT> ipv4only=on;

Preventing Future Errors

• Validate Nginx configuration before restarting services using sudo nginx -t.
• Use tools like ip monitor to track interface statuses and prevent unexpected downtime.
• Bind Nginx to all available interfaces with:

  listen *:<PORT>;
• Implement monitoring solutions like Nagios or Zabbix to detect and alert binding issues.
• Maintain records of network and server configuration changes to aid future

  troubleshooting.

• Validate configurations in non-production environments before deployment.
• Keep Nginx and the operating system updated to ensure compatibility and fix known bugs.

[Need assistance with a different issue? Our team is available 24/7.]

Conclusion

The “bind() to IP failed” error in Nginx can disrupt web services but is often straightforward to fix with the right approach. By understanding the causes, applying targeted solutions, and adopting best practices, we can minimize downtime and maintain a robust web server environment.

In brief, our Support Experts demonstrated how to fix “Nginx Error 99: Cannot assign requested address”.