SOLVED Re: finding netmask for "arbitrary" ip address

[jasonl]

Here's what I ended up doing; it does require Socket.pm, but from what I've seen so far that looks pretty standard. It uses inet_aton to convert ip, net, and mask to structs, &s them to compare, then returns the mask when it finds a hit.

use Socket;
sub findMask {
    my ($ip, $nets) = @_;

    my ($net, $mask) = ();

    foreach my $i (@$nets) {
        ($net, $mask) = split(m[/], $i);

        my $netBin = inet_aton($net);
        my $maskBin = inet_aton($mask);

        my $maskedNet = ($netBin & $maskBin);

        if (((inet_aton($ip)) & $maskBin) eq $maskedNet) {
            return "$mask";
        }
    }

    ## no match
    return -1;
}