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Difficulty: Very hardDNS Infrastructure and Record Types

A client workstation needs to connect to an external server via FQDN. The workstation's local DNS cache is empty. Sequence the complete recursive and iterative DNS resolution steps in the exact order they occur, from the client's initial request to the receipt and caching of the final IP address response.

  1. 1The stub resolver on the client workstation sends a recursive DNS query over UDP port 53 to its configured local recursive DNS resolver.
  2. 2The recursive DNS resolver sends an iterative query to a root DNS name server using root hints to locate the authoritative servers for the Top-Level Domain (TLD).
  3. 3The root name server responds with a referral containing the NS and glue records for the TLD name servers.
  4. 4The recursive DNS resolver queries the TLD name server, which returns NS records pointing to the authoritative name servers for the requested domain.
  5. 5The recursive DNS resolver queries the domain's authoritative name server and receives an answer containing the requested resource record.
  6. 6The recursive DNS resolver sends the IP address back to the stub resolver, and both components store the answer in their local DNS caches according to the record's TTL.

Answer

The correct sequence starts with the stub resolver sending a recursive query to the local recursive resolver, followed by iterative queries up the DNS hierarchy (Root server referral to TLD server, TLD server referral to Authoritative server, Authoritative server response), ending with the response returned to the stub resolver and cached locally.
The correct order follows the standard DNS resolution model: a client stub resolver initiates a recursive query to its local resolver. The local resolver then performs iterative lookups descending the hierarchy starting at the Root server, moving to the TLD server, and finally contacting the Authoritative server. Once the authoritative answer is retrieved, it is returned to the client and cached by both the local resolver and the client stub resolver.

Step-by-Step Solution

1
Initiate query from client
The client stub resolver sends a recursive query to the designated local recursive resolver.
The client operating system delegates full resolution responsibility to the recursive resolver.
2
Query Root Name Server
The local recursive resolver sends an iterative query to a Root DNS server.
With an empty cache, the recursive resolver must start at the DNS root.
3
Receive TLD Referral
The Root DNS server responds with NS and glue records pointing to the TLD servers.
Root servers only provide referrals to TLD servers rather than final IP mapping.
4
Query TLD Name Server
The local recursive resolver queries the TLD server and receives NS records for the authoritative server.
TLD servers maintain records pointing to the authoritative servers for registered domain names.
5
Query Authoritative Name Server
The local recursive resolver queries the authoritative server and receives the final resource record (A/AAAA).
Authoritative servers host the actual DNS zone data and supply definitive answers.
6
Return Response & Cache
The recursive resolver delivers the IP address to the stub resolver, and the entry is cached.
Caching prevents repetitive full tree traversal for subsequent requests during the TTL period.

Key Concept

DNS Resolution Hierarchy & Iterative vs Recursive Query Flow
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Topics

DNS Infrastructure and Record Types

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