sub octets2num {
    my $val= 0;
    for(  split /\./, shift(@_)  ) {
        $val= 0x100*$val + $_;
    }
    return $val;
}
sub num2octects {
    my $val= shift(@_);
    my @bytes;
    while(  0 < $val  ) {
        unshift @bytes, $val%0x100;
        $val= int( $val / 0x100 );
    }
    return ! @bytes ? "0" : join ".", @bytes
}