Recursive Resolver
A recursive resolver (also known as a DNS recursor) is a DNS server that acts as a middleman between a client and DNS nameservers. When you try to visit a website, the recursive resolver receives your request and takes full responsibility for tracking down the IP address by querying multiple DNS servers as needed. It handles the entire lookup process on your behalf and caches the results for faster future lookups.
How it works
A recursive DNS resolver is the first stop in a DNS query. It receives domain name requests from client devices and takes full responsibility for resolving them into IP addresses. The resolver queries multiple DNS servers if necessary, following the DNS hierarchy from root servers through TLD servers to authoritative servers, all without requiring any additional action from the client.
The recursive resolution process works as follows:
**1. Client Query:**
Your device sends a DNS query for
www.example.com to your configured recursive resolver (typically provided by your ISP or services like Google DNS 8.8.8.8 or Cloudflare 1.1.1.1)
**2. Cache Check:**
The resolver first checks its cache to see if it recently resolved this domain. If found and not expired (based on TTL), it returns the cached IP address immediately. This is the fastest path and happens in milliseconds.
**3. Root Server Query (if cache miss):**
If no cached answer exists, the resolver queries one of the 13 root DNS servers, asking for www.example.com. The root server responds with the IP addresses of the .com TLD nameservers.
**4. TLD Server Query:**
The resolver then queries a .com TLD server, which responds with the IP addresses of the authoritative nameservers for example.com.
**5. Authoritative Server Query:**
Finally, the resolver queries example.com's authoritative nameserver, which provides the IP address for www.example.com.
**6. Response and Caching:**
The resolver returns the IP address to your device and caches it for the duration specified by the record's TTL. The entire process typically completes in milliseconds.
**Key Difference - Recursive vs. Iterative:**
In recursive queries, the resolver does all the work - clients ask once and get a final answer. In iterative queries, the resolver would instead return referrals, making the client responsible for following up with each server.Key Points
- Recursive resolvers perform the entire DNS lookup process on behalf of clients
- They query root servers, TLD servers, and authoritative servers in sequence
- Results are cached based on TTL to improve performance for subsequent queries
- Common public recursive resolvers include Google DNS (8.8.8.8), Cloudflare (1.1.1.1), and Quad9 (9.9.9.9)
- Most users automatically use their ISP's recursive resolver unless they manually configure a different one
Common Use Cases
- Internet Browsing: Every time you visit a website, your browser uses a recursive resolver to convert domain names into IP addresses needed to load the page
- DNS Performance Optimization: Large recursive resolvers with extensive caches can provide faster DNS responses than small local resolvers with limited caching capacity
- Content Filtering and Security: Some recursive resolvers (like OpenDNS or Quad9) provide content filtering, blocking malicious domains, and parental controls
- Privacy Enhancement: Privacy-focused recursive resolvers (like Cloudflare 1.1.1.1) don't log queries and may use DNS over HTTPS (DoH) to prevent ISP snooping
code Example Recursive DNS Lookup Flow
| Type | Host / Name | Value / Points to | TTL |
|---|---|---|---|
| Step 1 | Client → Resolver | Query: www.example.com | — |
| Step 2 | Resolver → Root Server | Where is .com? | — |
| Step 3 | Resolver → TLD Server | Where is example.com? | — |
| Step 4 | Resolver → Auth Server | What is www.example.com? | — |
| Step 5 | Resolver → Client | 192.0.2.1 | 3600 |
* This example shows how a recursive resolver queries multiple servers to resolve www.example.com.
Frequently Asked Questions
What is the difference between a recursive resolver and an authoritative nameserver?expand_more
A recursive resolver is a middleman that performs DNS lookups on behalf of clients by querying other servers. An authoritative nameserver is the final source of truth that actually stores and provides the official DNS records for a domain. Think of it this way: recursive resolvers ask questions and search for answers, while authoritative nameservers provide the definitive answers. Recursive resolvers are at the beginning of the DNS query, authoritative servers are at the end.
Can I change my recursive resolver?expand_more
Yes, you can configure your device or router to use different recursive resolvers instead of your ISP's default. Popular options include Google DNS (8.8.8.8 and 8.8.4.4), Cloudflare (1.1.1.1 and 1.0.0.1), and Quad9 (9.9.9.9). Each offers different features - some focus on speed, others on privacy, blocking malware, or content filtering. You can change this in your network settings or router configuration.
Why would someone use a public recursive resolver instead of their ISP's?expand_more
People switch to public recursive resolvers for several reasons: faster performance (large providers have better caching and infrastructure), improved privacy (some ISPs log or monetize DNS queries), security features (blocking malware and phishing domains), reliability (redundant infrastructure with better uptime), and access (some ISPs use DNS-based censorship that public resolvers bypass). However, using non-ISP resolvers may route traffic differently and potentially increase latency to CDN content.
How does caching work in recursive resolvers?expand_more
When a recursive resolver successfully resolves a domain, it stores (caches) the answer for the duration specified by the record's TTL (Time to Live). If another client queries the same domain before the TTL expires, the resolver returns the cached answer immediately without querying other servers again. This dramatically improves performance and reduces load on authoritative servers. Popular domains may stay cached for hours, while less-visited domains might have shorter TTLs.
What happens if a recursive resolver goes down?expand_more
If your primary recursive resolver becomes unavailable, your device will typically try the secondary resolver you've configured (if any). Most operating systems and routers let you configure multiple DNS servers for redundancy. If all configured resolvers are unreachable, you'll be unable to access websites by domain name (though you could still access them by IP address if you know it). This is why it's recommended to configure at least two recursive resolvers in your network settings.