Edit: /usr/local/bin/iptab (982B)
#!/usr/bin/perl
eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
if 0; # not running under some shell
use Net::IP;
use strict;
print "+----------------------------------------------+
| addrs bits pref class mask |
+----------------------------------------------+
";
my ($ip,$size,$class,$bits,$len);
my $ip = new Net::IP('0');
for my $len (reverse (0..32))
{
$ip->set("0.0.0.0/$len");
$size = $ip->size();
if ($size >=1048576) # 1024*1024
{
$size /= 1048576;
$size .= 'M';
}
elsif ($size >= 1024)
{
$size /= 1024;
$size .= 'K';
};
$len = $ip->prefixlen();
$bits = 32 - $len;
if ($bits >= 24)
{
$class = 2**($bits-24);
$class.= 'A';
}
elsif ($bits >= 16)
{
$class = 2**($bits-16);
$class.= 'B';
}
elsif ($bits >= 8)
{
$class = 2**($bits-8);
$class.= 'C';
}
printf ("| %5s %6s %6s %7s %-15s |\n",
$size,$bits,'/'.$len,$class,$ip->mask());
};
print "+----------------------------------------------+\n";