Is there a way to calculate a CIDR
given a Sub net mask
using any Java lib
/function/trick?? I have been looking for a while and all I can find is from CIDR -> Netmask
and I need it the other way arround Netmask -> CIDR
... Im not that handy on Java
, but im willing to read a lot =) thnx guys
PzP =)
Whipped up a quick example. This converts an InetAddress
into a cidr value, it also validates that the InetAddress
represents a valid netmask.
The test input is 255.255.128.0
. The output cidr is 17
.
package com.stackoverflow._19531411;
import java.net.InetAddress;
public class NetmaskToCIDR {
public static int convertNetmaskToCIDR(InetAddress netmask){
byte[] netmaskBytes = netmask.getAddress();
int cidr = 0;
boolean zero = false;
for(byte b : netmaskBytes){
int mask = 0x80;
for(int i = 0; i < 8; i++){
int result = b & mask;
if(result == 0){
zero = true;
}else if(zero){
throw new IllegalArgumentException("Invalid netmask.");
} else {
cidr++;
}
mask >>>= 1;
}
}
return cidr;
}
public static void main(String[] args) throws Exception {
InetAddress netmask = InetAddress.getByName("255.255.128.0");
System.out.println(convertNetmaskToCIDR(netmask));
}
}
Credit for psuedocode @ https://stackoverflow.com/a/10090956/260633