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Display IP Address Allocation Table According to Subnet Mask

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. Following information is displayed with the command:
=> CIDR notation

=> Network Mask

=> Available Networks

=> Available Hosts per network

=> Total usable hosts

$ 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 (download link):

#!/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";

Sysadmin because even developers need heroes!!!

Linux Iptables Avoid IP Spoofing And Bad Addresses Attacks

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