In this tutorial, we will demonstrate you on how to convert IP address ranges into CIDR format.
What is CIDR
CIDR, which stands for Classless Inter-Domain Routing, is a method used for efficiently allocating and routing IP addresses on the internet. It was introduced to overcome some limitations of the original IP addressing system, which relied on fixed-size address classes (Class A, B, and C) and led to inefficient use of address space. An example of CIDR notation, 8.8.8.0/24, which represents the IP ranges from 8.8.8.0 to 8.8.8.255.
CIDR allows for a more flexible allocation of IP addresses by using a prefix notation. In CIDR notation, an IP address is followed by a forward slash (“/”) and a number representing the length of the network prefix. The notation looks like this: IP_address/prefix_length. For example, 192.168.1.0/24 indicates a network with a 24-bit prefix, meaning the first 24 bits represent the network address, and the remaining 8 bits are available for host addresses.
Please take note that this tutorial only for the conversion of IPv4 to CIDR format. We will not display you a complete project, but the core function of how the conversion work.
This function, iprange2cidr, takes 2 input parameters, namely the ipStart and ipEnd, the starting and the ending of an IP address respectively. You can either supply the IP address in dotted format, for example, 202.186.13.4, or IP number, for example, 3401190660, as the input parameters. The function will convert them into IP number if the dotted IP address format was supplied and perform the calculation.
Below are the sample codes of the function written in several programming languages, such as PHP, VB.NET, C#, Java and Ruby.
<?php
function iprange2cidr($ipStart, $ipEnd){
if (is_string($ipStart) || is_string($ipEnd)){
$start = ip2long($ipStart);
$end = ip2long($ipEnd);
}
else{
$start = $ipStart;
$end = $ipEnd;
}
$result = array();
while($end >= $start){
$maxSize = 32;
while ($maxSize > 0){
$mask = hexdec(iMask($maxSize - 1));
$maskBase = $start & $mask;
if($maskBase != $start) break;
$maxSize--;
}
$x = log($end - $start + 1)/log(2);
$maxDiff = floor(32 - floor($x));
if($maxSize < $maxDiff){
$maxSize = $maxDiff;
}
$ip = long2ip($start);
array_push($result, "$ip/$maxSize");
$start += pow(2, (32-$maxSize));
}
return $result;
}
function iMask($s){
return base_convert((pow(2, 32) - pow(2, (32-$s))), 10, 16);
}
?>
Public Function IPrange2cidr(ByVal ipStart As String, ipEnd As String) As List(Of String)
Dim startIP As Long = IP2Long(ipStart)
Dim endIP As Long = IP2Long(ipEnd)
Dim result As List(Of String) = New List(Of String)
While (endIP >= startIP)
Dim maxSize As Byte = 32
While (maxSize > 0)
Dim mask As Long = IMask(maxSize - 1)
Dim maskBase As Long = startIP And mask
If maskBase <> startIP Then
Exit While
End If
maxSize -= 1
End While
Dim x As Double = Math.Log(endIP - startIP + 1) / Math.Log(2)
Dim maxDiff As Byte = (32 - Math.Floor(x))
If maxSize < maxDiff Then
maxSize = maxDiff
End If
Dim ip As String = Long2IP(startIP)
result.Add(ip + "/" + Convert.ToString(maxSize))
startIP += Math.Pow(2, (32 - maxSize))
End While
Return result
End Function
Public Function IPrange2cidr(ByVal ipStart As Integer, ipEnd As Integer) As List(Of String)
Dim startIP As Long = ipStart
Dim endIP As Long = ipEnd
Dim result As List(Of String) = New List(Of String)
While (endIP >= startIP)
Dim maxSize As Byte = 32
While (maxSize > 0)
Dim mask As Long = IMask(maxSize - 1)
Dim maskBase As Long = startIP And mask
If maskBase <> startIP Then
Exit While
End If
maxSize -= 1
End While
Dim x As Double = Math.Log(endIP - startIP + 1) / Math.Log(2)
Dim maxDiff As Byte = (32 - Math.Floor(x))
If maxSize < maxDiff Then
maxSize = maxDiff
End If
Dim ip As String = Long2IP(startIP)
result.Add(ip + "/" + Convert.ToString(maxSize))
startIP += Math.Pow(2, (32 - maxSize))
End While
Return result
End Function
Private Function IMask(ByVal s As Integer) As Long
Return Math.Pow(2, 32) - Math.Pow(2, (32 - s))
End Function
Private Function IP2Long(ByVal ipAddress As String) As Long
Dim ip As System.Net.IPAddress = Net.IPAddress.Parse(ipAddress)
Return (CLng(ip.GetAddressBytes(0)) << 24) Or (CInt(ip.GetAddressBytes(1)) << 16) Or (CInt(ip.GetAddressBytes(2)) << 8) Or ip.GetAddressBytes(3)
End Function
Private Function Long2IP(ByVal ipAddress As Long) As String
Dim tmpIP As New Net.IPAddress(ipAddress)
Dim bytes() As Byte = tmpIP.GetAddressBytes()
Array.Reverse(bytes)
Dim addr As Long = CLng(BitConverter.ToUInt32(bytes, 0))
Return New Net.IPAddress(addr).ToString()
End Function
public static List<string> iprange2cidr(string ipStart, string ipEnd)
{
long start = ip2long(ipStart);
long end = ip2long(ipEnd);
var result = new List<string>();
while (end >= start)
{
byte maxSize = 32;
while (maxSize > 0)
{
long mask = iMask(maxSize - 1);
long maskBase = start & mask;
if (maskBase != start)
{
break;
}
maxSize--;
}
double x = Math.Log(end - start + 1) / Math.Log(2);
byte maxDiff = (byte)(32 - Math.Floor(x));
if (maxSize < maxDiff)
{
maxSize = maxDiff;
}
string ip = long2ip(start);
result.Add(ip + "/" + maxSize);
start += (long)Math.Pow(2, (32 - maxSize));
}
return result;
}
public static List<string> iprange2cidr(int ipStart, int ipEnd)
{
long start = ipStart;
long end = ipEnd;
var result = new List<string>();
while (end >= start)
{
byte maxSize = 32;
while (maxSize > 0)
{
long mask = iMask(maxSize - 1);
long maskBase = start & mask;
if (maskBase != start)
{
break;
}
maxSize--;
}
double x = Math.Log(end - start + 1) / Math.Log(2);
byte maxDiff = (byte)(32 - Math.Floor(x));
if (maxSize < maxDiff)
{
maxSize = maxDiff;
}
string ip = long2ip(start);
result.Add(ip + "/" + maxSize);
start += (long)Math.Pow(2, (32 - maxSize));
}
return result;
}
private static long iMask(int s)
{
return (long)(Math.Pow(2, 32) - Math.Pow(2, (32 - s)));
}
private static string long2ip(long ipAddress)
{
System.Net.IPAddress ip;
if (System.Net.IPAddress.TryParse(ipAddress.ToString(), out ip))
{
return ip.ToString();
}
return "";
}
private static long ip2long(string ipAddress)
{
System.Net.IPAddress ip;
if (System.Net.IPAddress.TryParse(ipAddress, out ip))
{
return (((long)ip.GetAddressBytes()[0] << 24) | ((long)ip.GetAddressBytes()[1] << 16) | ((long)ip.GetAddressBytes()[2] << 8) | ip.GetAddressBytes()[3]);
}
return -1;
}
public static List<String> iprange2cidr( String ipStart, String ipEnd ) {
long start = ip2long(ipStart);
long end = ip2long(ipEnd);
ArrayList<String> result = new ArrayList<String>();
while ( end >= start ) {
byte maxSize = 32;
while ( maxSize > 0) {
long mask = iMask( maxSize - 1 );
long maskBase = start & mask;
if ( maskBase != start ) {
break;
}
maxSize--;
}
double x = Math.log( end - start + 1) / Math.log( 2 );
byte maxDiff = (byte)( 32 - Math.floor( x ) );
if ( maxSize < maxDiff) {
maxSize = maxDiff;
}
String ip = long2ip(start);
result.add( ip + "/" + maxSize);
start += Math.pow( 2, (32 - maxSize) );
}
return result;
}
public static List<String> iprange2cidr( int ipStart, int ipEnd ) {
long start = ipStart;
long end = ipEnd;
ArrayList<String> result = new ArrayList<String>();
while ( end >= start ) {
byte maxSize = 32;
while ( maxSize > 0) {
long mask = iMask( maxSize - 1 );
long maskBase = start & mask;
if ( maskBase != start ) {
break;
}
maxSize--;
}
double x = Math.log( end - start + 1) / Math.log( 2 );
byte maxDiff = (byte)( 32 - Math.floor( x ) );
if ( maxSize < maxDiff) {
maxSize = maxDiff;
}
String ip = long2ip(start);
result.add( ip + "/" + maxSize);
start += Math.pow( 2, (32 - maxSize) );
}
return result;
}
private static long iMask(int s) {
return Math.round(Math.pow(2, 32) - Math.pow(2, (32 - s)));
}
private static long ip2long(String ipstring) {
String[] ipAddressInArray = ipstring.split("\\.");
long num = 0;
long ip = 0;
for (int x = 3; x >= 0; x--) {
ip = Long.parseLong(ipAddressInArray[3 - x]);
num |= ip << (x << 3);
}
return num;
}
private static String long2ip(long longIP) {
StringBuffer sbIP = new StringBuffer("");
sbIP.append(String.valueOf(longIP >>> 24));
sbIP.append(".");
sbIP.append(String.valueOf((longIP & 0x00FFFFFF) >>> 16));
sbIP.append(".");
sbIP.append(String.valueOf((longIP & 0x0000FFFF) >>> 8));
sbIP.append(".");
sbIP.append(String.valueOf(longIP & 0x000000FF));
return sbIP.toString();
}
require 'ipaddr'
def iprange2cidr(ipstart, ipend)
if ipstart.kind_of?(String) || ipend.kind_of?(String)
startR = ip2long(ipstart)
endR = ip2long(ipend)
else
startR = ipstart
endR = ipend
end
result = Array.new
while endR >= startR do
maxSize = 32
while maxSize > 0 do
mask = (iMask(maxSize - 1))
maskBase = startR & mask
if maskBase != startR
break
end
maxSize-=1
end
x = Math.log(endR - startR + 1)/Math.log(2)
maxDiff = (32 - x.floor).floor
if maxSize < maxDiff
maxSize = maxDiff
end
ip = long2ip(startR)
cidr = [ip, maxSize].join('/')
result.push cidr
startR += 2**(32-maxSize)
end
return result
end
def iMask(s)
return (2**32 - 2**(32-s))
end
def long2ip(num)
return IPAddr.new(num, Socket::AF_INET).to_s
end
def ip2long(ip)
return IPAddr.new(ip).to_i
end
The result that return by the iprange2cidr function is an Array that contains the list of CIDR formatted IP address. Looping has to be done to get all the CIDR formatted IP address from the return result. The following figure shows the sample output with ipStart:192.168.1.0 and ipEnd:192.168.1.9 of the converting IP address ranges into CIDR format.
192.168.1.0/29 192.168.1.8/31
The CIDR Calculator
A CIDR calculator is a tool used in networking to facilitate the efficient management of IP addresses. It allows users to perform calculations related to Classless Inter-Domain Routing (CIDR), a method for allocating and routing IP addresses.
With a CIDR calculator, users can easily subnet IP address ranges, determine network and broadcast addresses, and aggregate multiple IP ranges into a single CIDR notation. These calculators are valuable for network administrators and engineers in planning and optimizing IP address allocations, enhancing routing efficiency, and ensuring the scalability of network designs. Additionally, CIDR calculators serve as educational tools for learning and practicing subnetting and IP address management concepts.
Get free IP address tool to translate IPv4 address range into CIDR or visit the IP2Location.io CLI tool for more usage examples. You can also use the IP2Location.io CLI tool to obtain IP address information.
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