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Difficulty: MediumDNS Lookup and Name Resolution Roles in Enterprise Networks

An internal host in an enterprise network queries the corporate DNS server to resolve the Fully Qualified Domain Name (FQDN) of an external cloud service. The internal DNS server does not hold the authoritative zone file for the requested external domain. Assuming standard recursive resolution is enabled on the server, which action does the internal DNS server take to resolve the query for the client?

  1. It queries external DNS servers on behalf of the host by following the DNS hierarchy until it receives the answer and returns it to the host.Answer
  2. B
    It converts the client's query into TCP transport mode before forwarding it to ensure reliability when contacting root name servers.
  3. C
    It sends a DHCP relay message containing the IP address of an external public DNS server so the client can query the internet directly.
  4. D
    It rejects the query immediately because non-authoritative domain lookups are blocked by implicit deny rules unless a CNAME record exists.

Answer

The internal DNS server queries external DNS servers on behalf of the host by traversing the DNS hierarchy until it receives the answer and returns it to the host.
In enterprise networks, an internal DNS server configured for recursion acts as a recursive resolver for LAN clients. When a host requests resolution for a domain that the server is not authoritative for, the server performs the iterative lookups across external DNS servers (Root, TLD, and Authoritative) on behalf of the client and returns the resolved IP address.

Step-by-Step Solution

1
Analyze the role of a recursive DNS server in enterprise name resolution.
A recursive DNS resolver accepts queries from local host clients and resolves names for domains outside its local authority.
Internal hosts are generally configured to point to an internal recursive resolver rather than querying root internet DNS servers directly.
2
Trace the recursive DNS lookup flow for non-authoritative external domains.
The internal DNS server queries the DNS hierarchy (Root →\rightarrow Top-Level Domain →\rightarrow Authoritative Server) on behalf of the requesting host.
Recursion delegates the responsibility of traversing the global DNS tree to the DNS server rather than forcing the client to issue iterative queries.
3
Return the final response to the host client.
Once the authoritative answer is returned to the enterprise DNS server, it caches the record and sends the IP resolution back to the host.
This process provides seamless name resolution and allows the enterprise server to cache records locally for future requests.

Key Concept

Recursive DNS Query Resolution Flow and Server Roles
Estimated Time:1m 0s
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Topics

DNS Lookup and Name Resolution Roles in Enterprise Networks

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