As far as I can tell the default blocking method in current builds is NXDOMAIN. You can read the details directly from the PiHole official page [0]. Short versi

As far as I can tell the default blocking method in current builds is NXDOMAIN. You can read the details directly from the PiHole official page [0]. Short version, it just returns a no such domain. More info on blocking modes [1]. This says the default (and recommended) blocking mode is NULL but it wasn't the case when I recently did my last install. Not sure if it was something with my build or maybe the docs need to be updated. You will find that failing to access the resource on the other side will make many clients try and try again. On my PiHole I see Philips Hue, Microsoft, or Sonos with tens of thousands of retries triggered by previous failures to contact their destinations. [0] https://pi-hole.net/2018/05/18/nxdomain-and-null-blocking-with-ftldns/ https://pi-hole.net/2018/05/18/nxdomain-and-null-blocking-wi... [1] https://docs.pi-hole.net/ftldns/blockingmode/ https://docs.pi-hole.net/ftldns/blockingmode/