sub isValidIP {
    my $ip = shift;
    if ( ($a,$b,$c,$d) = $ip =~ m/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/ ) {
        if (($a|$b|$c|$d) < 256 ) {
            return 1;
        }
    }
    return 0;
}