use Socket;

sub next_subnet {
  my ($network, $subnet) = @_;

  my $inet = unpack('N', inet_aton($network));
  my $mask = unpack('N', inet_aton($netmask));
  my $ones = unpack('N', inet_aton('255.255.255.255'));

  my $size = ($ones ^ $mask) + 1;
  my $next = $inet + $size;

  return inet_ntoa(pack('N', $next));
}