Recursive Resolver
A recursive resolver is the DNS server your computer asks when it needs to convert a name like example.com to an IP address. The resolver walks the DNS hierarchy on your behalf: querying the root, then the TLD nameservers, then the authoritative nameservers for the domain: and returns the final answer.
Recursive vs authoritative
- Recursive resolvers answer queries from end-users. They cache aggressively. Examples:
1.1.1.1,8.8.8.8, your ISP's DNS, your home router's DNS. - Authoritative nameservers hold the actual records for a zone. They answer "yes I'm authoritative for example.com, here's the record" and never cache other zones. Examples:
ns1.cloudflare.com, AWS Route 53 nameservers.
Walking the recursion manually
A recursive lookup for www.example.com from a cold cache takes roughly:
- Resolver asks a root server ("a.root-servers.net"): "where is
.com?" Root returns: "ask one of these 13 .com nameservers." - Resolver asks a .com nameserver: "where is example.com?" The TLD nameserver returns: "ask one of these nameservers (NS records for example.com)."
- Resolver asks one of example.com's authoritative nameservers: "what is the A record for www?" Authoritative returns the IP.
That's three round-trips for a cold lookup. The resolver caches each step, so the next query for anything under .com skips step 1, and the next query for anything under example.com skips step 2.
Why this matters for troubleshooting
When you change a DNS record, the change happens at the authoritative nameserver immediately. But the world doesn't see it immediately, because every recursive resolver in between is still serving its cached copy until the TTL expires. A "DNS propagation problem" is almost always a recursive-cache problem, not an authoritative-update problem.
Choosing a public resolver
If you're picking one for personal use, the trade-offs are roughly: Cloudflare 1.1.1.1 is fastest in most regions and doesn't log queries to disk; Quad9 9.9.9.9 blocks known malicious domains; Google 8.8.8.8 has the broadest ECS support (better GeoDNS results) but logs more aggressively; NextDNS and ControlD let you customize blocklists. WhereIsDNS queries all 14 in parallel so you can see how they differ for any given lookup.
What WhereIsDNS does
WhereIsDNS sends a DNS-over-HTTPS (DoH) query to each of 14 well-known recursive resolvers in parallel. Comparing their answers tells you whether the change has reached most of the world, or whether it's still being served stale by some operators. The per-resolver latency column shows you which ones are fastest from the perspective of the Cloudflare edge that runs the queries.
Related: DNS caching · TTL · anycast.