How to check if an IP address is from a particular network/netmask in Java?

Question

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

Answer 1

I know this is very old question, but I stumbled upon this when I was looking to solve the same problem.

There is commons-ip-math library that I believe does a very good job. Please note that as of May 2019, there hasn't been any updates to the library (Could be that its already very mature library). Its available on maven-central

It supports working with both IPv4 and IPv6 addresses. Their brief documentation has examples on how you can check if an address is in a specific range for IPv4 and IPv6

Example for IPv4 range checking:

        String input1 = "192.168.1.0";
        Ipv4 ipv41 = Ipv4.parse(input1);

        // Using CIDR notation to specify the networkID and netmask
        Ipv4Range range = Ipv4Range.parse("192.168.0.0/24");
        boolean result = range.contains(ipv41);
        System.out.println(result); //false

        String input2 = "192.168.0.251";
        Ipv4 ipv42 = Ipv4.parse(input2);

        // Specifying the range with a start and end.
        Ipv4 start = Ipv4.of("192.168.0.0");
        Ipv4 end = Ipv4.of("192.168.0.255");
        range = Ipv4Range.from(start).to(end);

        result = range.contains(ipv42); //true
        System.out.println(result);