Question

Difficulty: MediumDNS Infrastructure and Record Types

A network systems engineer is configuring name resolution for a newly deployed dual-stack web server. Workstations on the corporate network can successfully connect to the server over IPv4 using the hostname `app.finance.net`. However, IPv6 connectivity attempts fail because the hostname does not resolve to an IPv6 address.

To troubleshoot, the engineer executes the following diagnostic query from a workstation:

text
$ dig AAAA app.finance.net +short

The command produces no output, whereas running `dig A app.finance.net +short` returns `172.16.40.25`.

Which resource record type must be configured in the authoritative DNS zone file to enable host name resolution to the server's IPv6 address?

  1. An AAAA record mapping app.finance.net to the server's 128-bit IPv6 addressAnswer
  2. B
    A PTR record mapping the IPv4 address 172.16.40.25 to the server's IPv6 address
  3. C
    A CNAME record mapping app.finance.net to port 53 on the IPv6 host
  4. D
    A TXT record defining the socket transport protocol for IPv6 DNS queries

Answer

An AAAA record mapping the hostname directly to the server's 128-bit IPv6 address must be added to the zone file.
In DNS infrastructure, forward name resolution for IPv6 endpoints requires an AAAA (Quad-A) record, which maps a fully qualified domain name (FQDN) to a 128-bit IPv6 address. Because `dig AAAA app.finance.net` returned no answer, creating an AAAA record in the authoritative zone file directly resolves the issue.

Step-by-Step Solution

1
Analyze the diagnostic command output
The dig AAAA query returned an empty response, confirming no Quad-A record exists for app.finance.net.
When a DNS server has an A record but lacks an AAAA record for a hostname, IPv6-capable clients cannot resolve the IPv6 endpoint address.
2
Determine the appropriate DNS record type required for IPv6 forward lookup
An AAAA (quad-A) record is required to map a domain hostname to a 128-bit IPv6 address.
Standard IPv4 forward resolution uses A records (32-bit), whereas IPv6 forward resolution requires AAAA records (128-bit).

Key Concept

DNS Record Types for Dual-Stack (IPv4/IPv6) Name Resolution
Estimated Time:1m 15s
Rate this question