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Fixing the Installation Error: Server Does Not Accept Subnet CIDR in Ubuntu 18.04

Ubuntu 10

In this article, we will delve into the intricacies of resolving the installation error: “Server Does Not Accept Subnet CIDR in Ubuntu 18.04”. This error typically occurs when you are attempting to install a server with a fixed IP address using the provided ISO of Ubuntu 18.04.3, but the specified subnet CIDR and IP address are not correctly set.

Quick Answer

To fix the "Server Does Not Accept Subnet CIDR" error in Ubuntu 18.04, you need to enter the correct subnet CIDR and IP address during the installation process. Make sure the IP address is within the specified subnet, and remember that the subnet CIDR is not the same as the subnet mask.

Understanding the Subnet CIDR

Before we jump into the solution, it’s crucial to understand what a Subnet CIDR is. CIDR stands for Classless Inter-Domain Routing. It is a method for allocating IP addresses and routing Internet Protocol packets. The subnet CIDR represents the network segment your device is on, along with its gateway.

The error message you received indicates that the IP address is not contained within the specified subnet CIDR. It’s important to note that the subnet CIDR is not the same as the subnet mask.

Calculating the Correct Subnet CIDR

To calculate the correct subnet CIDR, you can use a subnet calculator or follow the steps below:

  1. Convert the subnet mask 255.255.252.0 to binary: 11111111.11111111.11111100.00000000.
  2. Count the number of fixed bits in the binary representation. In this case, there are 22 fixed bits.
  3. Write the IP address and the subnet CIDR in CIDR notation, separated by a slash. For example, 10.16.192.252/22.

Alternatively, you can specify the subnet CIDR separately from the IP address. In this case, the subnet CIDR would be 10.16.192.0/22.

Resolving the Installation Error

To fix the issue, you need to enter the correct subnet CIDR and IP address during the installation process. This ensures that the IP address is within the specified subnet. Here’s how:

  1. During the installation process, when prompted, enter the subnet CIDR as 10.16.192.0/22.
  2. Next, enter the IP address as 10.16.192.252.

Please note that the subnet field refers to the network segment and gateway, not the subnet mask.

By following these steps, you should be able to resolve the “Server Does Not Accept Subnet CIDR” error in Ubuntu 18.04.

Conclusion

Understanding the concept of subnet CIDR and how to calculate it correctly is crucial when setting up a server on Ubuntu 18.04. By ensuring that the IP address is within the specified subnet, you can avoid the “Server Does Not Accept Subnet CIDR” error during installation.

Remember that the subnet CIDR is not the same as the subnet mask, and the subnet field during installation refers to the network segment and gateway, not the subnet mask.

For more in-depth information on subnet CIDR and IP addressing, you can refer to the official Ubuntu documentation.

What is the difference between subnet CIDR and subnet mask?

Subnet CIDR and subnet mask serve similar purposes, but they are different. Subnet CIDR represents the network segment and gateway in CIDR notation, while the subnet mask is used to determine the network and host portions of an IP address. Subnet CIDR is written as an IP address followed by a slash and the number of fixed bits, while the subnet mask is written as four sets of numbers separated by periods (e.g., 255.255.255.0).

Can I use a subnet calculator to calculate the correct subnet CIDR?

Yes, you can use a subnet calculator to calculate the correct subnet CIDR. Subnet calculators are online tools that help you determine the network address, broadcast address, and other subnet details based on the IP address and subnet mask. They can simplify the process of calculating the subnet CIDR, especially for complex networks.

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