Validate an IP Address (with Mask)

Question

I have ip addresses and a mask such as 10.1.1.1/32. I would like to check if 10.1.1.1 is inside that range. Is there a library or utility that would do

Answer 1

Thanks to John Kugelman--I used his code snippets to create this class.

package bs;

import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.UnknownHostException;

/**
 * Represents an IP range based on an address/mask.
 * @author Scott Plante, using code snippets by John Kugelman.
 */
public class IPMask
{
  public static void main(String args[]) 
      throws UnknownHostException
  {
    IPMask ipmask;

    ipmask = IPMask.getIPMask("192.168.20.32/24");
    System.out.println("Checking "+ipmask+"...");

    test(ipmask, "192.168.20.31 ", true);
    test(ipmask, "192.168.20.32 ", true);
    test(ipmask, "192.168.20.33 ", true);
    test(ipmask, "192.168.20.34 ", true);
    test(ipmask, "192.168.20.35 ", true);
    test(ipmask, "192.168.20.36 ", true);
    test(ipmask, "192.168.20.254", true);
    test(ipmask, "192.168.20.157", true);
    test(ipmask, "192.168.21.1  ", false);
    test(ipmask, "192.168.19.255", false);
    test(ipmask, "192.168.24.1  ", false);

    ipmask = IPMask.getIPMask("192.168.20.32/31");
    System.out.println("Checking "+ipmask+"...");

    test(ipmask, "192.168.20.31 ", false);
    test(ipmask, "192.168.20.32 ", true);
    test(ipmask, "192.168.20.33 ", true);
    test(ipmask, "192.168.20.34 ", false);
    test(ipmask, "192.168.20.35 ", false);
    test(ipmask, "192.168.20.36 ", false);
    test(ipmask, "192.168.20.254", false);
    test(ipmask, "192.168.20.157", false);
    test(ipmask, "192.168.21.1  ", false);
    test(ipmask, "192.168.19.255", false);
    test(ipmask, "192.168.24.1  ", false);

    ipmask = IPMask.getIPMask("192.168.20.32/23");
    System.out.println("Checking "+ipmask+"...");

    test(ipmask, "192.168.20.31 ", true);
    test(ipmask, "192.168.20.32 ", true);
    test(ipmask, "192.168.20.33 ", true);
    test(ipmask, "192.168.20.254", true);
    test(ipmask, "192.168.21.254", true);
    test(ipmask, "192.168.19.255", false);
    test(ipmask, "192.168.24.1  ", false);

  }

  public static void test(IPMask ipmask, String addr, boolean expect) 
      throws UnknownHostException
  {
    boolean got = ipmask.matches(addr);
    System.out.println(addr + "\t(" + expect + ") ?\t"+got
        + "\t" + (got==expect?"":"!!!!!!!!"));
  }

  private Inet4Address i4addr;
  private byte maskCtr;

  private int addrInt;
  private int maskInt;

  public IPMask(Inet4Address i4addr, byte mask)
  {
    this.i4addr = i4addr;
    this.maskCtr = mask;

    this.addrInt = addrToInt(i4addr);
    this.maskInt = ~((1 << (32 - maskCtr)) - 1);
  }

  /** IPMask factory method. 
   * 
   * @param addrSlashMask IP/Mask String in format "nnn.nnn.nnn.nnn/mask". If 
   *    the "/mask" is omitted, "/32" (just the single address) is assumed.
   * @return a new IPMask
   * @throws UnknownHostException if address part cannot be parsed by 
   *    InetAddress
   */
  public static IPMask getIPMask(String addrSlashMask) 
      throws UnknownHostException
  {
    int pos = addrSlashMask.indexOf('/');
    String addr;
    byte maskCtr;
    if (pos==-1)
    {
      addr = addrSlashMask;
      maskCtr = 32;
    }
    else
    { 
      addr = addrSlashMask.substring(0, pos);
      maskCtr = Byte.parseByte(addrSlashMask.substring(pos + 1));
    }
    return new IPMask((Inet4Address) InetAddress.getByName(addr), maskCtr);
  }

 /** Test given IPv4 address against this IPMask object.
   * 
   * @param testAddr address to check.
   * @return true if address is in the IP Mask range, false if not.
   */  
  public boolean matches(Inet4Address testAddr)
  {
    int testAddrInt = addrToInt(testAddr);   
    return ((addrInt & maskInt) == (testAddrInt & maskInt));
  }

/** Convenience method that converts String host to IPv4 address.
   * 
   * @param addr IP address to match in nnn.nnn.nnn.nnn format or hostname.
   * @return true if address is in the IP Mask range, false if not.
   * @throws UnknownHostException if the string cannot be decoded.
   */
  public boolean matches(String addr) 
      throws UnknownHostException
  {
    return matches((Inet4Address)InetAddress.getByName(addr));
  }

/** Converts IPv4 address to integer representation.
   */
  private static int addrToInt(Inet4Address i4addr)
  {
    byte[] ba = i4addr.getAddress();  
    return (ba[0]       << 24) 
        | ((ba[1]&0xFF) << 16) 
        | ((ba[2]&0xFF) << 8) 
        |  (ba[3]&0xFF);
  }

  @Override
  public String toString()
  {
    return "IPMask(" + i4addr.getHostAddress() + "/" + maskCtr + ")";
  }

  @Override
  public boolean equals(Object obj)
  {
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    final IPMask that = (IPMask) obj;    
    return (this.addrInt == that.addrInt && this.maskInt == that.maskInt);
  }

  @Override
  public int hashCode()
  {
    return this.maskInt + this.addrInt;
  }

}

I did have to add a mask to the int conversion in his code:

Inet4Address a = (Inet4Address) InetAddress.getByName("192.192.192.192");
byte[]       b = a.getAddress();
int          i = (b[0] << 24) | (b[1] << 16) | (b[2] << 8) | (b[3] << 0);
System.out.println(Integer.toHexString(i));
System.out.println(Integer.toHexString(addrToInt(a)));

Produced:

ffffffc0
c0c0c0c0

On my system:

$> uname -a
Linux guin 2.6.37.6-0.5-desktop #1 SMP PREEMPT 2011-04-25 21:48:33 +0200 x86_64 x86_64 x86_64 GNU/Linux
$> java -version
java version "1.6.0_25"
Java(TM) SE Runtime Environment (build 1.6.0_25-b06)
Java HotSpot(TM) 64-Bit Server VM (build 20.0-b11, mixed mode)
$> 

You can remove the main and test methods from the above class. They're adapted from the unit test code and added here for simplicity.