4. Write a program to demonstrate subnetting and find the subnet masks.

Download The write up here

import java.io.*;
import java.net.InetAddress;
public class Subnet1 {

    public static void main(String[] args) throws IOException {
   
        System.out.println("ENTER IP:");
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String ip = br.readLine();
        String checkclass = ip.substring(0, 3);



        int cc = Integer.parseInt(checkclass);
        String mask = null;
        if(cc>0)
        {
            if(cc<=127)
            {
                mask = "255.0.0.0";
        System.out.println("Class A IP Address");
        System.out.println("SUBNET MASK:\n"+mask);
            }
            if(cc>=128 && cc<=191)
            {
                mask = "255.255.0.0";
        System.out.println("Class B IP Address");
        System.out.println("SUBNET MASK:\n"+mask);
            }
            if(cc>=192 && cc<=223)
            {
                mask = "255.255.255.0";
        System.out.println("Class C IP Address");
        System.out.println("SUBNET MASK:\n"+mask);
            }
        if(cc>=224 && cc<=239)
            {
        mask = "255.0.0.0";
                System.out.println("Class D IP Address Used for multicasting");
            }
            if(cc>=240 && cc<=254)
            {
        mask = "255.0.0.0";
                System.out.println("Class E IP Address Experimental Use");
            }
        }
      

        String networkAddr="";
    String lastAddr="";
        String[] ipAddrParts=ip.split("\\.");
        String[] maskParts=mask.split("\\.");

        for(int i=0;i<4;i++){
        int x=Integer.parseInt(ipAddrParts[i]);
        int y=Integer.parseInt(maskParts[i]);
        int z=x&y;
        networkAddr+=z+".";
    int w=z|(y^255);
    lastAddr+=w+".";
        }
   
    System.out.println("First IP of block: "+networkAddr);
    System.out.println("Last IP of block: "+lastAddr);
   }

}

/*OUTPUT
iotlab@iotlab-Veriton-M200-B360:~$ javac Subnet1.java
iotlab@iotlab-Veriton-M200-B360:~$ java Subnet1
ENTER IP:
226.35.65.23
Class D IP Address Used for multicasting
First IP of block: 226.0.0.0.
Last IP of block: 226.255.255.255.
iotlab@iotlab-Veriton-M200-B360:~$ java Subnet1
ENTER IP:
192.168.100.5
Class C IP Address
SUBNET MASK:
255.255.255.0
First IP of block: 192.168.100.0.
Last IP of block: 192.168.100.255.
iotlab@iotlab-Veriton-M200-B360:~$
*/