2001:4860:4860::8888 is the IPv6 address of Google Public DNS — the IPv6 equivalent of 8.8.8.8. Google's DNS resolver accepts queries over both IPv4 and IPv6. Systems configured to use Google DNS with IPv6 connectivity will use this address for DNS queries.
Privacy note
Seeing 2001:4860:4860::8888 in a DNS leak test means your system is using Google DNS over IPv6. Like the IPv4 version, this is a common cause of DNS leaks on VPNs that don't handle IPv6 DNS properly.
Frequently asked questions about 2001:4860:4860::8888
Who owns 2001:4860:4860::8888?
2001:4860:4860::8888 is operated by Google LLC. The ASN is AS15169.
Where is 2001:4860:4860::8888 located?
Based on geolocation data, 2001:4860:4860::8888 is associated with Mountain View, California, United States. IP geolocation is approximate and may differ from the physical server location.