Cannot assign requested address [SOLVED]

The "Cannot Assign Requested Address" error is quiet common in the network community and can be seen in various network-related and application specific contexts. Here are some of the common areas where this error is seen more often:

1. Web Servers:
   • Nginx: When Nginx tries to bind to an IP address not present on the server, or if the port is already in use.
   • Apache: Similar to Nginx, trying to bind to an unavailable IP or a busy port.
2. Database Servers:
   • Redis: Occurs when Redis is configured to bind to a specific IP that isn’t available.
   • MySQL: If MySQL is set up to listen on an IP not assigned to the server.
3. Networking Applications:
   • SSH: Attempting to bind to an IP address for listening or forwarding ports that isn’t available.
   • FTP Servers: Similar issues when they are set to bind to specific IPs or ports.
4. DNS Services:
   • BIND: The DNS server attempting to bind to an IP address that does not exist on the local machine.
5. Mail Servers:
   • Postfix: When trying to bind to a non-existent IP address for receiving or sending emails.
6. VPN Services:
   • OpenVPN: Trying to use an IP address for the VPN server that isn’t configured on the server.
7. Containers and Virtualization:
   • Docker: When a Docker container tries to bind to an IP not available on the host machine.
   • Kubernetes: Similar issues when pods/services are configured with specific IPs.
8. Development Tools:
   • Local development servers (like those started by web frameworks such as Django or Flask) trying to bind to an IP address that the development machine does not have configured.
9. Gaming Servers:
   • Game servers (like Minecraft, Counter-Strike) that are set to bind to a specific IP address or port which might be restricted or already in use.
10. Peer-to-Peer Applications:
    • Applications that try to bind to a port for incoming connections which might already be in use or blocked by a firewall.

In this tutorial we will try to cover most of these areas and cover the cause of getting "Cannot Assign Requested Address" error and how to solve the same in individual application:

 

Troubleshooting "cannot assign requested address" Error

1. Validate Configuration

The "cannot assign requested address" error often occurs if application is configured to bind to an IP address that isn't assigned to any network interface on the server. You need to check the configuration file based on your application:

• Nginx: Typically found at /etc/nginx/nginx.conf and /etc/nginx/conf.d/*.conf for additional server block configurations. Look out for listen directive for IP and port settings.
• Apache: Commonly located at /etc/httpd/conf/httpd.conf for CentOS/RHEL or /etc/apache2/apache2.conf and /etc/apache2/ports.conf for Debian/Ubuntu systems. Look out for Listen for IP and port configurations.
• Redis: Usually /etc/redis/redis.conf. Look out for bind and port.
• MySQL: Typically /etc/my.cnf, /etc/mysql/my.cnf, or contained within /etc/mysql/mysql.conf.d/. Look out for bind-address and port.
• SSH: Check in /etc/ssh/sshd_config and look out for ListenAddress and Port.
• FTP Servers: Depends on the software; for vsftpd it's /etc/vsftpd.conf. Look out for listen and listen_port.
• BIND: Main configuration file is /etc/named.conf or /etc/bind/named.conf. Look out for listen-on.
• Postfix: Main configuration file is /etc/postfix/main.cf. Look out for inet_interfaces and smtp_bind_address.
• OpenVPN: Configuration file usually found in /etc/openvpn/server.conf. Look out for local for IP address binding.

Consider Nginx as an example, open the Nginx configuration file (usually located at /etc/nginx/nginx.conf or under /etc/nginx/sites-available/) and verify the listen directive:

server {
    listen 192.168.1.100:80;
    server_name example.com;
}

Make sure the IP address in the listen directive is correct and available on your server.

Check if the IP address (e.g., 192.168.1.100) is assigned to the server:

ip addr show

This command lists all IPs assigned to your server. If 192.168.1.100 is not listed, that's likely the cause of your error. If the IP address is not on your machine, either assign that IP to the server through your network settings or change the IP in the Nginx configuration to one that is available on your server.

If the listen directive in your Nginx configuration does not specify an IP address and is simply set to listen on a port across all interfaces, like this:

server {
    listen 80;
    server_name example.com;
}

Restart Nginx to ensure all settings are correctly applied:

sudo systemctl restart nginx

Similarly you can check your application's Listen directive to make sure it is listening on proper interface address.

 

2. Check for Port conflict

It is possible that the port which your application is using is already in use by some other application service. You can use tools like netstat or ss command to check for port conflicts.

For example using netstat command:

sudo netstat -tulpn | grep :<port>

If this gives an output then it would mean that the port is already in use. Similarly you can also use ss command:

ss -tuln | grep :<port>

If the port is already in use then you can either stop the service which is using your application port or alternatively you can configure your application to run on a different port number.

The configuration file details are provided in previous section for different services, after making the changes you can restart your application service.

 

3. Troubleshoot SELinux Issues

If you suspect that SELinux is causing issues (like preventing application service from binding to a port), you can check the audit logs to see the SELinux denials:

sudo ausearch -m avc -ts recent

If there are no hints in the log file then you can also plan to change the mode of SELinux temporarily (until the next reboot) using:

sudo setenforce 1  # Set to enforcing
sudo setenforce 0  # Set to permissive

When SELinux is in permissive mode, it continues to log violations to its policies as it would in enforcing mode, but it does not enforce the policies—meaning it allows actions that would otherwise be blocked.

After executing the above commands the changes will be applied immediately and a reboot is not required. You can e-verify your application status to see if this fixes "cannot assign requested address" error. Once you've replicated the issue in permissive mode, you can check the SELinux logs to see what would have been blocked. These logs are typically found in /var/log/audit/audit.log. You can use tools like audit2why to analyze these logs:

sudo grep AVC /var/log/audit/audit.log | audit2why

This command will show you the SELinux denials that occurred, along with explanations of why each action was denied under normal enforcing mode. This information is crucial for understanding what policies need to be adjusted.

To change the SELinux mode permanently, you will need to edit the SELinux configuration file:

sudo nano /etc/selinux/config

In this file, change the SELINUX= line to either enforcing, permissive, or disabled. For example:

SELINUX=enforcing

After making this change, you need to reboot your system for the changes to take effect. You can also read selinux changes to be persistent for more information.