--- a/services/univention-s4-connector/conffiles/etc/univention/s4connector/s4/mapping.py	
+++ a/services/univention-s4-connector/conffiles/etc/univention/s4connector/s4/mapping.py	
@@ -1103,7 +1103,7 @@ 
 ignore_filter = ''
 for dns in configRegistry.get('connector/s4/mapping/dc/ignorelist', '').split(','):
 	if dns:
-		ignore_filter += '(%s)' % (dns)
+		ignore_filter += '(cn=%s)' % (dns)
 if ignore_filter:
 	print "			ignore_filter='(|%s)'," % ignore_filter
 @!@