Over the weekend, I updated my wireless router to the latest revision of ASUSWRT-Merlin. I also decided to update my DietPi Pi-hole to their latest builds. Due to a full code rewrite of Dietpi, it meant a complete rebuild for that system. The release of ASUSWRT-Merlin also suggested resetting to factory defaults due to some major changes. Everything was about to be new again.
Once I got everything rebuilt and running, I noticed requests coming from my firewall to my dietpi every 10 seconds or so for dns.msftncsi.com. I immediately assumed this was some Microsoft telemetry noise on my network from MS NLA. However, the queries were coming directly from my firewall which seemed odd. Another search led me to a post on the Pi-hole discourse. After I ran nvram show | grep dns_probe, it was clear I found the culprit.
admin@gw:/tmp/home/root# nvram show | grep dns_probe dns_probe_host=dns.msftncsi.com dns_probe_content=18.104.22.168 fd3e:4f5a:5b81::1
I ran the following three lines and confirmed the traffic stopped. No reboot was necessary. The first post I read recommended setting dns_probe_content to 0.0.0.0 and dns_probe_host to “” (effectively blank). I later found a post by RMerlin that explains setting dns_probe_content to blank disables the watchdog service but effectively disables the dual WAN feature. It would make sense that dual WAN would require a watchdog service. So, if you use dual WAN, don’t do this. Otherwise, you should be fine.
admin@gw:/tmp/home/root# nvram set dns_probe_content= admin@gw:/tmp/home/root# nvram set dns_probe_host= admin@gw:/tmp/home/root# nvram commit