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

The open-source IPAddress Java library will do this in a polymorphic manner for both IPv4 and IPv6 and handles subnets. Disclaimer: I am the project manager of that library.

Example code:

contains("10.10.20.0/30", "10.10.20.3");
contains("10.10.20.0/30", "10.10.20.5");
contains("1::/64", "1::1");
contains("1::/64", "2::1");
contains("1::3-4:5-6", "1::4:5");       
contains("1-2::/64", "2::");
contains("bla", "foo");

static void contains(String network, String address) {
    IPAddressString one = new IPAddressString(network);
    IPAddressString two = new IPAddressString(address);
    System.out.println(one +  " contains " + two + " " + one.contains(two));
}

Output:

10.10.20.0/30 contains 10.10.20.3 true
10.10.20.0/30 contains 10.10.20.5 false
1::/64 contains 1::1 true
1::/64 contains 2::1 false
1::3-4:5-6 contains 1::4:5 true
1-2::/64 contains 2:: true
bla contains foo false