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Difficulty: MediumDNS Infrastructure and Record Types

A client workstation attempts to resolve the domain name `www.example.com`, which is not stored in any local cache. Arrange the steps of the un-cached recursive DNS resolution process in the correct chronological order from first to last.

  1. 1The client stub resolver sends a recursive query for `www.example.com` to its configured local recursive DNS resolver.
  2. 2The local recursive resolver queries a Root Name Server to obtain the referral IP address for the `.com` Top-Level Domain (TLD) name server.
  3. 3The local recursive resolver queries the `.com` TLD Name Server to get the authoritative name server IP address for `example.com`.
  4. 4The local recursive resolver queries the authoritative name server of `example.com` to retrieve the `A` record for `www.example.com`.
  5. 5The local recursive resolver caches the resource record and returns the resolved IP address to the client stub resolver.

Answer

The correct chronological sequence begins with the client stub resolver querying the local recursive resolver, followed by iterative queries from the recursive resolver to the Root Name Server, the TLD Name Server, and the Authoritative Name Server, ending with the recursive resolver caching the record and sending the IP address back to the client.
The standard DNS resolution flow follows a strict top-down traversal when host cache is empty: Stub Resolver → Recursive Resolver → Root Name Server → TLD Name Server → Authoritative Name Server → Recursive Resolver (cache & reply) → Client.

Step-by-Step Solution

1
Client initiates lookup
The client stub resolver sends a recursive request for `www.example.com` to the local recursive DNS server.
Client operating systems offload full resolution tasks to designated recursive DNS servers.
2
Query Root Name Server
The recursive resolver sends an iterative query to a root server and receives a referral to the `.com` TLD server.
Root servers direct resolvers to the appropriate Top-Level Domain servers based on the domain suffix.
3
Query TLD Name Server
The recursive resolver sends an iterative query to the `.com` TLD server and receives a referral to `example.com` authoritative name servers.
TLD servers maintain delegation records pointing to domain-level authoritative servers.
4
Query Authoritative Name Server
The recursive resolver queries the authoritative name server for `example.com` and retrieves the requested `A` host record.
Authoritative servers store the master zone data and yield definitive record responses.
5
Respond to client and cache
The recursive resolver stores the host mapping in local cache according to TTL and returns the IP address to the client.
Caching minimizes network latency for subsequent queries while delivering the final answer to the requesting application.

Key Concept

Recursive DNS Resolution Hierarchy
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Topics

DNS Infrastructure and Record Types

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