How to obtain CIDR IP notation from IP and subnet using Perl

Question

Is there a Perl function that, given an IP address and subnet mask, can return the CIDR notation of the subnet the IP belongs to?

For example, assuming I have the IP 192.168.1.23 with subnet mask 255.255.255.0 , I want to obtain the value 192.168.1.0/24 .

Or if I have 192.168.1.23 with subnet mask 255.255.255.224 I want 192.168.1.0/27 and so on.

I could eventually build a function that does so, but I find hard to believe there isn't something that does this already.

Answer 1

I recommend that you use the NetAddr::IP module. It's a simple matter of constructing an object with the required IP address and net mask and calling the network method on it

It looks like this

use strict;
use warnings 'all';
use feature 'say';

use NetAddr::IP;

say make_cidr(qw/ 192.168.1.23  255.255.255.0 /);
say make_cidr(qw/ 192.168.1.23  255.255.255.224 /);

sub make_cidr {
    my ($addr, $mask) = @_;
    my $net = NetAddr::IP->new($addr, $mask);
    $net->network;
}

output

192.168.1.0/24
192.168.1.0/27

Answer 2

If you want a prepackaged solution, you can use the addrandmask2cidr function from Net::CIDR .

If you want to roll your own, the basic algorithm is to count the number of set bits in the mask to get the value after the slash (eg, 255.255.255.0 is 11111111.11111111.11111111.00000000 in binary, 24 bits set, therefore CIDR /24) and do a logical-and ( & ) of the address with the mask to get the network's base address.