How to correctly set the subnet mask installing Linux Ubuntu 20.04 server? ERROR: '172.16.182.216' is not contained in '255.255.255.0/24'

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20-10-2024

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When installing Linux Ubuntu 20.04 Server, you may encounter an error message like this:

ERROR: '172.16.182.216' is not contained in '255.255.255.0/24'

This error indicates that the IP address you are attempting to assign to your server is not compatible with the given subnet mask. In this article, we will explore how to correctly set the subnet mask to avoid such issues during installation and ensure your server is configured for optimal network performance.

Understanding the Problem

In the example above, the IP address 172.16.182.216 cannot be associated with the subnet mask 255.255.255.0/24. The subnet mask 255.255.255.0 corresponds to the CIDR notation /24, which means that only the IP addresses from 172.16.182.0 to 172.16.182.255 are valid within that network segment. However, 172.16.182.216 is actually within the range specified by this subnet mask, which indicates a different issue.

The Real Issue

The error arises because the IP address you are trying to use might belong to a different subnet. For example, if your network uses the 172.16.182.0/24 subnet and you have defined your network configuration incorrectly, this can lead to conflicting setups that cause the installation process to fail.

Setting the Subnet Mask Correctly

To set the correct subnet mask during the installation of Ubuntu Server, follow these steps:

1. Determine the Network Address Range: Before installation, you need to know the range of IP addresses available in your network. This can be done by consulting your network administrator or checking the existing configurations of your network devices.

2. Choose an Appropriate IP Address: Ensure that the IP address you wish to assign to your server falls within the correct subnet range. For example, if your network is 172.16.182.0/24, you can assign an IP between 172.16.182.1 and 172.16.182.254 (with the .0 reserved for the network address and .255 typically reserved for broadcast).

3. Set the Correct Subnet Mask: During the installation process, when prompted to configure the network settings, make sure to enter a subnet mask that corresponds to your chosen IP address. For example, if you are using 172.16.182.1, set the subnet mask to 255.255.255.0.

Example of Network Configuration

Here is an example of how you should configure your network settings:

• IP Address: 172.16.182.10
• Subnet Mask: 255.255.255.0
• Gateway: 172.16.182.1
• DNS: 8.8.8.8 (Google's public DNS server)

Additional Considerations

• VLANs and Subnets: If your network uses VLANs or multiple subnets, be sure that your chosen IP and subnet mask align with the configured settings of your other devices.
• DHCP Configuration: If your network uses DHCP, it’s often simpler to allow the server to obtain an IP address automatically. Ensure that the DHCP server is configured to provide a valid IP address to the server during installation.

Troubleshooting Tips

1. Check IP Address Conflicts: Use tools like ping or nmap to ensure the IP address is not already in use.
2. Verify Subnet Configuration: Double-check the subnet mask and IP address range using ipcalc or a similar tool to avoid errors.
3. Review Logs: If you encounter issues after installation, check system logs like /var/log/syslog for network-related errors.

Useful Resources

• Ubuntu Official Documentation
• Understanding IP Addresses and Subnet Masks
• DigitalOcean Networking Basics

By following the guidance above and understanding the importance of correct subnet configuration, you will enhance your Linux Ubuntu Server installation experience. Configuring your server with the right settings ensures stable network communication and avoids common pitfalls associated with IP addressing. Happy server configuring!