Drupal Installation running without settings.php (multisite)
Have a look at sites.php in your sites folder.

 $sites = array(
   'devexample.com' =&gt; 'example.com',
   'localhost.example' =&gt; 'example.com',
 );



  The above array will cause Drupal to look for a directory named 
  "example.com" in the sites directory whenever a request comes from 
  "example.com", "devexample.com", or "localhost/example".


So in your case you should have 'drupal.abcd.com' =&gt; 'default'

The reason why its picking up settings file from abcd.com is because when a request comes for drupal.abcd.com it looks for folder drupal.abcd.com since that folder is not there it will look for next match like abcd.com and it picks it up from there.

I am not sure about Drupal 7 site set up but playing around with sites.php should fix it.