Linux - IP Address Allocation Table script

If you need a tabular representation of relationships and source of the various variables representing a chunk from /32 to /0 subnets use iptab command. This is useful if you are allocating IPs to end users.

$ iptab
Sample output:

+----------------------------------------------+
| addrs bits pref class mask |
+----------------------------------------------+
| 1 0 /32 255.255.255.255 |
| 2 1 /31 255.255.255.254 |
| 4 2 /30 255.255.255.252 |
| 8 3 /29 255.255.255.248 |
| 16 4 /28 255.255.255.240 |
| 32 5 /27 255.255.255.224 |
| 64 6 /26 255.255.255.192 |
| 128 7 /25 255.255.255.128 |
| 256 8 /24 1C 255.255.255.0 |
| 512 9 /23 2C 255.255.254.0 |
| 1K 10 /22 4C 255.255.252.0 |
| 2K 11 /21 8C 255.255.248.0 |
| 4K 12 /20 16C 255.255.240.0 |
| 8K 13 /19 32C 255.255.224.0 |
| 16K 14 /18 64C 255.255.192.0 |
| 32K 15 /17 128C 255.255.128.0 |
| 64K 16 /16 1B 255.255.0.0 |
| 128K 17 /15 2B 255.254.0.0 |
| 256K 18 /14 4B 255.252.0.0 |
| 512K 19 /13 8B 255.248.0.0 |
| 1M 20 /12 16B 255.240.0.0 |
| 2M 21 /11 32B 255.224.0.0 |
| 4M 22 /10 64B 255.192.0.0 |
| 8M 23 /9 128B 255.128.0.0 |
| 16M 24 /8 1A 255.0.0.0 |
| 32M 25 /7 2A 254.0.0.0 |
| 64M 26 /6 4A 252.0.0.0 |
| 128M 27 /5 8A 248.0.0.0 |
| 256M 28 /4 16A 240.0.0.0 |
| 512M 29 /3 32A 224.0.0.0 |
| 1024M 30 /2 64A 192.0.0.0 |
| 2048M 31 /1 128A 128.0.0.0 |
| 4096M 32 /0 256A 0.0.0.0 |
+----------------------------------------------+

iptab is nothing but a perl script and part of perl-Net-IP package. Here is script listing :

#!/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";