Yes, using a regular expression is "much more efficient", but yours is in some cases, as you point out, incorrect. And using Net::IP::Match::Regexp you can still do more than sixty seven thousand comparisons per second (on my old and rusty laptop, anyway) if the regexp is initialized once only. So what do you want: 
$ cat 791149.pl
use strict;
use warnings;

use Net::IP::Match::Regexp qw( create_iprange_regexp match_ip );
use Benchmark qw / cmpthese /;

my $regexp_init_once =
  create_iprange_regexp( qw( 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 )
+ );

sub netip {
  my $regexp =
    create_iprange_regexp( qw( 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16
+ ) );
  return ( match_ip( $_[0], $regexp ) );
}

sub netip_init_once {
  return match_ip( $_[0], $regexp_init_once );
}

sub regexp {
  return $_[0] =~ /^(10\.\d+|172\.(1[6-9]|2\d|3[0-1])|192\.168)(\.\d+)
+{2}$/;
}

cmpthese(
  -1,
  {
    'netip'           => sub { netip('1.2.3.4') },
    'netip_init_once' => sub { netip_init_once('1.2.3.4') },
    'regexp'          => sub { regexp('1.2.3.4') },
  }
);

__END__
$ perl 791149.pl
                     Rate           netip netip_init_once          reg
+exp
netip              2438/s              --            -96%           -1
+00%
netip_init_once   67622/s           2674%              --            -
+95%
regexp          1390157/s          56918%           1956%             
+ --

[download]
--
No matter how great and destructive your problems may seem now, remember, you've probably only seen the tip of them. [1]

In reply to Re^3: Regexp: Private IP Addresses by andreas1234567
in thread Regexp: Private IP Addresses by Anonymous Monk

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