my $pre = '00:96:14:';
my ($minhex,$maxhex) = qw(0 2fffff);

# Randomize a number between $minhex and $maxhex, inclusive
# Accounts for a min value other than 0
my $hostiddec = int(rand(hex($maxhex) - hex($minhex) + 1)) + hex($minhex);

# Convert to hex again
$hostidhex = unpack("H*",pack("i",$hostiddec));

# Format, getting rid of leading 0's and adding colons
$hostidhex =~ s/^0*(\w{2})(\w{2})(\w{2})$/$1:$2:$3/;

# Output (return here rather than print if you're in a subroutine)
print $pre . $hostidhex;