Question

I’m trying to develop a script which will, in part, generate a list of MAC addresses from a given starting base. What I have as input is a list of MAC addresses, and need to increment by 1.

Examples:

00:1D:FE:12:37:1A (need to generate 00:1D:FE:12:37:1B)
00:1D:FE:12:37:49 (need to generate 00:1D:FE:12:37:4A)
00:1D:FE:12:37:4F (need to generate 00:1D:FE:12:37:50)

The restriction here is that I need to run this script on a machine that has no “extra” perl modules neither installed nor available, so the code would need to be included within the script. This means Net::MAC is out as a module, but I could potentially cannibalize some useful bits and include it but I’m thinking what I’m trying to do shouldn’t be entirely complex to implement in a small function utilizing pack(?) or something of the like.

I’ve found various threads around on forums like PerlMonks, but no one seems to have a conclusive answer. Any input would be appreciated!

Answer 1

It’s a 48-bit number. Parse it, increment it, format it.

Many Perl builds only support 32-bit numbers as integers, so I’ll avoid forming larger ints.

my $mac_str = '00:1D:FE:12:37:1A';

( my $mac_hex = $mac_str ) =~ s/://g;
my ($mac_hi, $mac_lo) = unpack("nN", pack('H*', $mac_hex));

if ($mac_lo == 0xFFFFFFFF) {
    $mac_hi = ($mac_hi + 1) & 0xFFFF;
    $mac_lo = 0;
} else {
    ++$mac_lo;
}

$mac_hex = sprintf("%04X%08X", $mac_hi, $mac_lo);
$mac_str = join(':', $mac_hex =~ /../sg);