149.112.112.112 is the secondary address.
Quad9 is run by a Swiss non-profit and doesn't log users' IP addresses. Its blocking comes from threat-intelligence feeds: a blocked name returns NXDOMAIN, so the browser shows an error like DNS_PROBE_FINISHED_NXDOMAIN. If a legitimate site fails only with Quad9, it may be a false positive; Quad9 has a form to report it.
Facts
- Address
- 9.9.9.9
- Owner
- Quad9 Foundation (Switzerland)
On a Mac
Add 9.9.9.9 and 149.112.112.112 (IPv6 2620:fe::fe) in System Settings › Network › Details › DNS. For an unfiltered version, use 9.9.9.10.
Frequently asked questions
What is 9.9.9.9?
Quad9's public DNS resolver, which blocks known malicious domains. It's run by a Swiss non-profit foundation.
Does Quad9 block ads?
No. It blocks malware, phishing and similar threats, not ads or trackers.
Why does a site not work with 9.9.9.9?
Quad9 may have it on a threat list. Check with dig @9.9.9.10 (unfiltered); if that works, report the false positive to Quad9.