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Question

Difficulty: MediumDNS Infrastructure and Record Types

A network administrator is deploying a web application server that operates exclusively on an IPv6 address (`2001:db8:85a3::8a2e:370:7334`). While workstations can access the application using the raw IPv6 address, attempting to connect using the hostname `app.corp.contoso.com` fails. The administrator inspects the internal authoritative DNS zone file and finds the following resource record entry:

text
app.corp.contoso.com. 3600 IN A 2001:db8:85a3::8a2e:370:7334

Which of the following configuration changes is required to resolve the hostname resolution issue?

  1. Replace the existing A record with an AAAA record mapping the hostname to the IPv6 address.Answer
  2. B
    Change the A record to a CNAME record with the canonical target set to the IPv6 address string.
  3. C
    Update the DNS server firewall rules to force all client hostname lookup queries to transmit over TCP instead of UDP.
  4. D
    Modify the DNS resource record parameter to redirect queries from port 53 to HTTP port 80.

Answer

Replace the existing A record with an AAAA record mapping the hostname to the IPv6 address.
Replacing the incorrect A record with an AAAA record allows the DNS server to return a valid 128-bit IPv6 address response to client queries requesting hostname resolution for `app.corp.contoso.com`. Standard A records are designed solely for 32-bit IPv4 addresses.

Step-by-Step Solution

1
Identify the host address family required for name resolution.
The server uses a 128-bit IPv6 address (`2001:db8:85a3::8a2e:370:7334`).
Different DNS resource record types are designed for specific network protocols and address formats.
2
Analyze the existing zone file configuration.
The zone contains an A record attempting to store an IPv6 address string.
Standard A records only accept 32-bit IPv4 dotted-decimal addresses and fail to parse or serve IPv6 addresses.
3
Select the correct DNS record type for IPv6 resolution.
Configure an AAAA record for `app.corp.contoso.com` pointing to the IPv6 address.
AAAA records are specifically designated in RFC 3596 for mapping hostnames to IPv6 addresses.

Key Concept

DNS Record Types for Host Address Resolution (A vs AAAA)
Estimated Time:1m 0s
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Topics

DNS Infrastructure and Record Types

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