# Subnetting (Java)

Problem Definition: Write a program to implement subnetting and find the subnet masks.

import java.util.Scanner;
class Subnet{
public static void main(String args[]){
Scanner sc = new Scanner(System.in);
String ip = sc.nextLine();
String split_ip[] = ip.split(“\\.”); //SPlit the string after every .
String split_bip[] = new String; //split binary ip
String bip = “”;
for(int i=0;i<4;i++){
split_bip[i] = appendZeros(Integer.toBinaryString(Integer.parseInt(split_ip[i]))); // “18” => 18 => 10010 => 00010010
bip += split_bip[i];
}
System.out.println(“IP in binary is “+bip);
System.out.print(“Enter the number of addresses: “);
int n = sc.nextInt();

int bits = (int)Math.ceil(Math.log(n)/Math.log(2)); /*eg if address = 120, log 120/log 2 gives log to the base 2 => 6.9068, ceil gives us upper integer */
System.out.println(“Number of bits required for address = “+bits);

int fbip[] = new int;
for(int i=0; i<32;i++) fbip[i] = (int)bip.charAt(i)-48; //convert cahracter 0,1 to integer 0,1
for(int i=31;i>31-bits;i–)//Get first address by ANDing last n bits with 0
fbip[i] &= 0;
String fip[] = {“”,””,””,””};
for(int i=0;i<32;i++)
fip[i/8] = new String(fip[i/8]+fbip[i]);
for(int i=0;i<4;i++){
System.out.print(Integer.parseInt(fip[i],2));
if(i!=3) System.out.print(“.”);
}
System.out.println();

int lbip[] = new int;
for(int i=0; i<32;i++) lbip[i] = (int)bip.charAt(i)-48; //convert cahracter 0,1 to integer 0,1
for(int i=31;i>31-bits;i–)//Get last address by ORing last n bits with 1
lbip[i] |= 1;
String lip[] = {“”,””,””,””};
for(int i=0;i<32;i++)
lip[i/8] = new String(lip[i/8]+lbip[i]);
for(int i=0;i<4;i++){
System.out.print(Integer.parseInt(lip[i],2));
if(i!=3) System.out.print(“.”);
}
System.out.println();
}
static String appendZeros(String s){
String temp = new String(“00000000”);
return temp.substring(s.length())+ s;
}
}

/*Output