Does anyone know a java component to check if IP address is from particular network/netmask?

Question

I need to determine if given IP address is from some special network i must authenticate automatically.

Answer 1

You can use the java network interface like so:

Enumeration<NetworkInterface> nets = NetworkInterface.getNetworkInterfaces();
    for (NetworkInterface netint : Collections.list(nets)){
        Enumeration<InetAddress> inetAddresses = netint.getInetAddresses();
        for (InetAddress inetAddress : Collections.list(inetAddresses)) {
            //check if inetAddress is from particular address
        }
    }

Answer 2

Jakarta Commons Net has org.apache.commons.net.util.SubnetUtils that appears to satisfy your needs. It looks like you do something like this:

SubnetInfo subnet = (new SubnetUtils("10.10.10.0", "255.255.255.128")).getInfo();
boolean test = subnet.isInRange("10.10.10.10");

Note, as carson points out, that Jakarta Commons Net has a bug that prevents it from giving the correct answer in some cases. Carson suggests using the SVN version to avoid this bug.

Answer 3

You can also try

boolean inSubnet = (ip & netmask) == (subnet & netmask);

or shorter

boolean inSubnet = (ip ^ subnet) & netmask == 0;