Discovery filters are inclusive-type filters, which mean that an autodiscovery candidate system must match an IP address of a discovery filter before it is eligible for discovery. Thus, you must create at least one discovery filter to use autodiscovery.
To prevent specific systems from being discovered, you can use the ipExcludeList parameter in the BASEDIR/smarts/conf/discovery/discovery.conf file to create exclude-type filters. The ability to create exclude-type filters simplifies the creation of the discovery filters.