What is a Recursive Query?

Updated on June 3, 2025

DNS queries link domain names like google.com to IP addresses. A key type is the recursive query, which resolves domain names step-by-step. This article explains how it works and why it matters.

Definition and Core Concepts

A recursive query is a type of DNS query where the DNS resolver (usually provided by an Internet Service Provider (ISP) or your operating system) is tasked with fully resolving the requested domain name. This means the resolver will communicate with other DNS servers to fetch the authoritative answer and return the final result (e.g., an IP address) to the client.

To better understand this mechanism, let’s break down some essential concepts:

• DNS Resolver: A server or software responsible for handling client-initiated DNS queries. It performs recursive tasks to provide the requested result.
• DNS Name Server: A server that holds DNS records and responds to queries by providing relevant information.
• Recursive Query (vs Iterative Query): A recursive query delegates the resolution responsibility entirely to the resolver. An iterative query, on the other hand, requires the client to request data from each DNS server step-by-step.
• Root Name Servers: The starting point for DNS resolution, helping locate Top-Level Domain (TLD) servers.
• Top-Level Domain (TLD) Servers: Name servers responsible for domains like .com, .org, or .edu.
• Authoritative Name Servers: Servers providing final answers for specific domain names.
• Caching: A technique used by DNS resolvers to store previously resolved queries for faster future responses.

Recursive Query Versus Iterative Query

The key difference between recursive and iterative queries lies in how the resolution process is managed:

• Recursive Query: The resolver handles all steps, communicating with multiple DNS servers until the final answer is reached, then returning it to the client.
• Iterative Query: The client receives partial answers and must query each subsequent DNS server directly until the resolution is complete.

How It Works

Now that we’ve covered the core concepts, let’s explore the step-by-step process of how a recursive query works:

1. The Client Sends a Recursive Query to the Resolver

When a user enters a domain name in their browser (e.g., example.com), a recursive query is sent to a DNS resolver. This is typically managed by an ISP or a public resolver like Google DNS (8.8.8.8) or Cloudflare (1.1.1.1).

2. The Resolver Queries the Root Server

The DNS resolver begins by contacting one of the 13 Root Name Servers globally available. These servers help direct queries to the appropriate TLD servers. For example, if the domain is “example.com,” the root server points the resolver to the .com TLD server.

3. The Resolver Queries the TLD Server

The resolver sends a query to the .com TLD server. This server provides the location of the Authoritative Name Server for the requested domain, in this case, “example.com.”

4. The Resolver Queries the Authoritative Server

Finally, the resolver queries the authoritative name server for “example.com.” This server contains the DNS records needed to resolve the domain’s IP address.

5. The Authoritative Server Responds to the Resolver

The authoritative server responds with the definitive IP address for “example.com,” such as 192.0.2.1.

6. The Resolver Caches the Response

To improve efficiency, the resolver stores (or caches) the resolved IP address locally. This caching reduces latency for future queries for the same domain.

7. The Resolver Responds to the Client

The cached or freshly resolved IP address is sent back to the client, allowing the requested website to load in the browser.

This seamless process typically takes milliseconds, ensuring speedy internet browsing.

Key Features and Components

Recursive queries come with unique features that distinguish them from other types of DNS operations:

• Client Delegation of Resolution: The client offloads all resolution responsibilities to the resolver.
• Single Client Query: Only one query is required from the client.
• Multiple Resolver Queries: Behind the scenes, the resolver performs multiple queries across DNS servers.
• Guaranteed Final Answer (if resolvable): The resolver guarantees to return either the requested IP address or an error message.
• Heavy Load on Resolvers: Recursive resolvers often handle high traffic loads, making them critical to DNS infrastructure.

Use Cases and Applications

Recursive queries play a significant role in various real-world scenarios:

• Web Browsing: Every time you type a URL like example.com, a recursive query ensures your browser connects to the correct IP address within seconds. 
• Email Communication: When sending an email, mail servers use recursive DNS queries to locate the recipient’s mail server by querying MX (Mail Exchange) records. 
• Application Connectivity: Modern applications use recursive DNS queries to connect with APIs, external servers, or third-party services, ensuring seamless performance for users.

Key Terms Appendix

Below is a glossary of technical terms discussed in this article:

• Recursive Query (DNS): A type of DNS query where the resolver fully resolves the client’s request.
• DNS Resolver: The entity responsible for handling client DNS queries and performing recursive tasks.
• DNS Name Server: A server that stores DNS records and responds to queries.
• Iterative Query (DNS): A query where the client sequentially requests data from each DNS server.
• Root Name Server: The first step in DNS resolution, pointing resolvers to TLD servers.
• Top-Level Domain (TLD) Server: DNS servers responsible for domains like .com or .org.
• Authoritative Name Server: The server that holds the definitive answer for a particular domain.
• Caching: The process of storing DNS responses for future use.