using System;

using System.Net;

public class Program

{

    public static void Main()

    {

        string ipAddressString = "173.160.21.227"; // Example IPv6 address

        string subnetMaskCIDR = "/30";

        string ipAddressStringCIDR = "173.140.21.21/30";

​

        string networkAddress = GetCorrectCIDR(ipAddressStringCIDR);

        //string test = GetNetworkAddress(ipAddressString, subnetMaskCIDR);

        //Console.WriteLine("GetNetworkAddress:" + test);

​

        if (networkAddress != null)

        {

            Console.WriteLine($"IP Address: {ipAddressString}");

            Console.WriteLine($"Subnet Mask (CIDR): {subnetMaskCIDR}");

            Console.WriteLine($"Network Address CIDR: {networkAddress}");

        }

        else

        {

            Console.WriteLine("Invalid IP address format.");

        }

    }

     public static string GetCorrectCIDR(string cidr)

 {

     var result = cidr;

     var cidrParts = cidr.Split('/');

​

     if (cidrParts.Length == 2)

     {

         var networkAddress = GetNetworkAddress(cidrParts[0], int.Parse(cidrParts[1])); 

         result = $"{networkAddress}/{cidrParts[1]}";

     }

     return result;

 }

​

 static string GetNetworkAddress(string ipAddressString, int prefixLength)

 {

     try

     {

         IPAddress ipAddress = IPAddress.Parse(ipAddressString);

​

         // Parse CIDR notation to get prefix length

         //int prefixLength = int.Parse(subnetMaskCIDR.Substring(1));

​

         // Calculate subnet mask based on prefix length

         byte[] subnetMaskBytes = ipAddress.GetAddressBytes();

​

         for (int i = prefixLength; i < subnetMaskBytes.Length * 8; i++)

         {

             int byteIndex = i / 8;

             int bitOffset = i % 8;

             subnetMaskBytes[byteIndex] &= (byte)~(1 << (7 - bitOffset));

         }

​

         IPAddress subnetMask = new IPAddress(subnetMaskBytes);

​

         // Perform bitwise AND to get the network address

         byte[] ipAddressBytes = ipAddress.GetAddressBytes();

         byte[] networkBytes = new byte[ipAddressBytes.Length];

​

         for (int i = 0; i < ipAddressBytes.Length; i++)

         {

             networkBytes[i] = (byte)(ipAddressBytes[i] & subnetMaskBytes[i]);

         }

​

         IPAddress networkAddress = new IPAddress(networkBytes);

         return networkAddress.ToString();

     }

     catch (FormatException)

     {

         return null; // Invalid IP address format

     }

 }

}