$re = '/(?<!^\h)(?<!^\h\h)(?<!^\h\h\h)(?<!\h\h\h\h)\b(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\b/m';
$str = '
1.blah
1.1 blah blah
1.1.1 blah blah blah my ip address is 192.168.1.1
1.1.1.1 blah blah blah blah (DLP thinks this is an IP Address and block the document)
On the 1. January the profit rate was 3.5 %, and by article 3.1.4. in the agreement we sent that information to 127.0.0.1
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php