Check whether the ipAddress is in private range

Question

How would I check to see whether the ip address is in private category ?

    if(isPrivateIPAddress(ipAddress)) {
                


        

Answer 1

First of all, Private networks can use IPv4 addresses anywhere in the following ranges:

• a) 192.168.0.0 - 192.168.255.255 (65,536 IP addresses)
• b) 172.16.0.0 - 172.31.255.255 (1,048,576 IP addresses)
• c) 10.0.0.0 - 10.255.255.255 (16,777,216 IP addresses)

As we can see from method isSiteLocalAddress in Inet4Address.java :

 public boolean isSiteLocalAddress() {
    // refer to RFC 1918
    // 10/8 prefix
    // 172.16/12 prefix
    // 192.168/16 prefix
    int address = holder().getAddress();
    return (((address >>> 24) & 0xFF) == 10)
        || ((((address >>> 24) & 0xFF) == 172)
            && (((address >>> 16) & 0xF0) == 16))
        || ((((address >>> 24) & 0xFF) == 192)
            && (((address >>> 16) & 0xFF) == 168));
}

So case b) 172.16.0.0 - 172.31.255.255 (1,048,576 IP addresses) is not satisfied. But you can easily write you own version of how to tell whether a address is private address.Here is my version:

import com.google.common.net.InetAddresses;

private static boolean isPrivateV4Address(String ip) {
    int address = InetAddresses.coerceToInteger(InetAddresses.forString(ip));
    return (((address >>> 24) & 0xFF) == 10)
            || ((((address >>> 24) & 0xFF) == 172) 
              && ((address >>> 16) & 0xFF) >= 16 
              && ((address >>> 16) & 0xFF) <= 31)
            || ((((address >>> 24) & 0xFF) == 192) 
              && (((address >>> 16) & 0xFF) == 168));
}