use Regexp::Common qw( net );

my %interesting_ips;
while( <IPS> ) {
  chomp;
  $interesting_ips{ $_ } = 1;
}

while( my $fw_line = <RULES> ) {
  while( my( $addr ) = $fw_line =~ m{($RE{net}{IPv4})}g ) {
    say qq{$.: found interesting address '$addr'} 
      if exists $interesting_ips{ $addr };
  }
}