Matching an ip address to a table of subnet masks... What is the best approach in Java?

Question

Here's the scenario... I have a table of subnets. (see below) I have an ip address. I would like to find out what subnet the ip address belongs to based on a lookup in the table. This association will then be used to determine what location the user is at. It's a private network space so the standard internet to location lookups wouldn't apply. What would be the best approach? Would I need to break the ip address into it's numeric parts and to a bitwise comparison against all the subnets.. or are there built-in tools in Java API that could make my life easier for comparing IP address to subnet mask?

I'm mainly looking for best way to compare ipaddress to a given subnetmask and determining yes this matches, or no it doesn't.. Optionally. Any tips on how to store the list and search with minimal operations would be appreciated also.

Ideally I'd be doing something similar to this:

List subnetInfo = null;

subnetInfo = findSubnet('192.168.0.1');  //value null if nothing found

....

//return null if nothing found
List findSubnet(String ipaddress) {
   List subnetDetails = null;
   .... code here ...
   return subnetDetails;
}

Table 1: Sample list of subnets

dk-ballerup-gen-off-v411        10.172.80.0/21  NANR-denmark-ballerup-metallbuen66-ground-first-floors-incl-dhcp-(sr14585203)
ae-dubai-ofssl-gen-off-v410  10.172.88.0/24  NANR-arab-emirates-ofssl-iflex-general-office-v410-(sr12781477)
ru-stpetersburg-gen-off-v411    10.172.89.0/24  NANR-russia-stpetersburg-general-office-incl-dhcp (bsteinba)

Answer 1

Apache Commons Net has a SubnetUtils for this sort of thing, including determining if a given IP address is within a given subnet.

Trivial example:

    String[] subnetsMasks = { ... };
    Collection<SubnetInfo> subnets = new ArrayList<SubnetInfo>();
    for (String subnetMask : subnetsMasks) {
        subnets.add(new SubnetUtils(subnetMask).getInfo());
    }

    String ipAddress = ...;
    for (SubnetInfo subnet : subnets) {
        if (subnet.isInRange(ipAddress)) {
            System.out.println("IP Address " + ipAddress + " is in range " + subnet.getCidrSignature());
        }
    }