What Primary, Secondary, and IPv6 DNS Addresses Mean on Public DNS Server

Updated

On publicdns.xyz, each provider is listed with a primary DNS server (sometimes called the preferred DNS server), a secondary DNS server (sometimes called the alternate DNS server), and, for many providers, one or more IPv6 addresses. The primary is the address your device queries first; the secondary is a fallback used when the primary is unreachable or too slow to respond. IPv6 addresses do the same job as the IPv4 addresses but are reached over IPv6 networks, so they only matter if your device and network actually support IPv6. The page also notes that primary and secondary servers can be "mixed and matched" to add another layer of redundancy — meaning you are not required to use two addresses from the same provider.

Primary vs. secondary: what actually changes

Role Also called When it is used Practical effect
Primary Preferred DNS First for every lookup Determines normal resolution speed and behavior
Secondary Alternate DNS Only when the primary fails or times out Keeps resolution working during an outage

The key point is that the secondary is not a load-balancer or a second opinion. Your device sends queries to the primary and only falls back to the secondary when the primary does not answer. So if you care about a specific provider's filtering or privacy policy, put that provider in the primary slot — the secondary only takes over in failure cases.

Because the two slots are independent, you can pair, for example, Cloudflare's primary (1.1.1.1) with Google's secondary (8.8.4.4). The page explicitly supports this: "Primary and secondary DNS servers can be 'mixed and matched' to provide another layer of redundancy." The trade-off is that your fallback traffic then goes to a different operator with a different privacy policy and different filtering, which may or may not be what you want.

IPv6 addresses: same role, different network

IPv6 DNS addresses appear in the same list because a device on an IPv6-capable network needs a DNS resolver it can reach over IPv6. If you enter only IPv4 DNS addresses on an IPv6-only or dual-stack connection, resolution may still work through translation, but native IPv6 DNS avoids that dependency.

Examples from the page:

  • Google Public DNS: 2001:4860:4860::8888 / 2001:4860:4860::8844
  • Cloudflare: 2606:4700:4700::1111 / 2606:4700:4700::1001
  • Quad9: 2620:fe::fe / 2620:fe::9

Some providers list only IPv4 (Level 3, Comodo Secure DNS, Norton ConnectSafe, SmartViper, Freenom World, Dyn, FreeDNS, Alternate DNS, 114DNS, OneDNS, DNSpai), and some list only IPv6 (CFIEC IPv6 Public DNS: 240c::6666 / 240c::6644). That is a property of what the provider publishes, not a ranking of quality.

Why some providers list both

Listing both IPv4 and IPv6 addresses lets you configure a dual-stack device so that DNS resolution works over whichever protocol is available. It also means the same provider can serve you if your network switches between IPv4 and IPv6. If your device or router has no IPv6 connectivity, the IPv6 entries are simply unused — entering them does no harm, but they will not help either.

How to use this in practice

  1. Decide which provider you want as your main resolver (based on speed, filtering, or privacy — the page itself does not rank them).
  2. Enter that provider's primary address in the preferred DNS field.
  3. Enter either the same provider's secondary address, or a different provider's address, in the alternate DNS field.
  4. If your device supports IPv6, add the matching IPv6 addresses in the IPv6 DNS fields.
  5. Save and reconnect, then verify resolution still works.

A concrete example: choosing Cloudflare as primary and Google as secondary gives you 1.1.1.1 (preferred) and 8.8.4.4 (alternate), with 2606:4700:4700::1111 and 2001:4860:4860::8844 for IPv6. This keeps resolution alive if Cloudflare is unreachable, at the cost of fallback queries going to Google.

Common points of confusion

  • "Secondary" does not mean slower or lower priority for normal traffic. It is idle until the primary fails.
  • Mixing providers is allowed but changes your privacy and filtering profile during failover.
  • IPv6 addresses are not "better" addresses. They are only usable on IPv6-capable connections.
  • A provider missing an IPv6 entry is not a defect. It reflects what that operator publishes.

The page's own summary covers the naming: primary DNS servers are sometimes called preferred DNS servers, secondary DNS servers are sometimes called alternate DNS servers, and DNS servers in general are referred to as DNS server addresses, internet DNS servers, DNS IP addresses, and similar terms — all describing the same two-slot configuration.