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Difficulty: MediumDNS Infrastructure and Record Types

A network administrator is configuring DNS records for an enterprise web service. The administrator needs to map the alias hostname `portal.corp.example.com` to the primary canonical domain name `webserver01.corp.example.com`, which ultimately resolves to IPv4 address `10.50.10.15`.

Review the DNS lookup query output below:

text
$ dig portal.corp.example.com

;; QUESTION SECTION:
;portal.corp.example.com. IN A

;; ANSWER SECTION:
portal.corp.example.com. 300 IN ???? webserver01.corp.example.com.
webserver01.corp.example.com. 300 IN A 10.50.10.15

Which DNS record type is represented by `????` in the lookup response?

  1. CNAMEAnswer
  2. B
    PTR
  3. C
    SRV
  4. D
    NS

Answer

The CNAME record type is used to map an alias domain name (portal.corp.example.com) to a canonical domain name (webserver01.corp.example.com).
A CNAME (Canonical Name) record is used in DNS to create an alias pointing one domain name to another true (canonical) domain name. In the provided dig output, portal.corp.example.com points to webserver01.corp.example.com, which subsequently resolves to IP address 10.50.10.15.

Step-by-Step Solution

1
Analyze the query output structure
The query requests an A record for portal.corp.example.com, but the first entry in the answer section maps portal.corp.example.com directly to another domain name (webserver01.corp.example.com).
Understanding how DNS chains resolutions requires examining the record relationship between the requested name and target name.
2
Identify the record type function
The record type that aliases one fully qualified domain name (FQDN) to another canonical FQDN is a Canonical Name (CNAME) record.
CNAME records allow multiple alias hostnames to point to a single canonical record without needing separate A/AAAA records for each host.

Key Concept

DNS Record Types and Functionality (CNAME vs. PTR/SRV/NS)
Estimated Time:1m 0s
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Topics

DNS Infrastructure and Record Types

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