if (
   my ($pairs) = $entry =~
      /^ \s* permit \s+ ip \s+ (?: host \s+ \S+ \s+ )? (.*)/x
) {
   while ( $pairs =~ /(\S+) \s+ (\S+)/xg ) {
      my ($ip, $mask) = ($1, $2);
      ... $ip ... $mask ...
   }
}