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.
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.
What WhereIsDNS does
WhereIsDNS queries 12 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.
Related: DNS caching · TTL · anycast.