I used in the past NetAddr::IP that understands cidrs and has the useful within method.

Example fragment:

 my $ip = new NetAddr::IP($address_given);
 my %nets;
 
 map { $nets{$_}= new NetAddr::IP($_),} qw( 192.168.0.0/29 10.10.10.0/
+24);
 foreach  my $k (keys %nets){

        if ($ip->within($nets{$k})) {
[download]

L*

I know there are modules out there, like Net::Netmask for instance, but I wonder if it could be achieved from core ?

Everything can be achieved from core. If you know a module (like Net::Netmask) which does what you want, simply inspect the source (and the source of its dependencies) and do it that way yourself.

FWIW, I like Net::CIDR::Lite.

I wonder if it could be achieved from core ? This is not a constraint, I'd like to have a discussion on this matter.

If there is a module, and it seems like there is, then what advantage would you gain from not using it? With a module, you get already tested code, with the possibility of updating the module independently, and so on...