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Difficulty: HardDNS Infrastructure and Record Types

A network systems administrator is auditing the public DNS zone configuration for an enterprise domain (enterprise.exampleenterprise.example) to support a new email server deployment. The administrator runs the following diagnostic command to inspect existing records:

text
; <<>> DiG 9.16.1-Ubuntu <<>> enterprise.example TXT
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41209
;; QUESTION SECTION:
;enterprise.example. IN TXT

;; ANSWER SECTION:
enterprise.example. 3600 IN TXT "v=spf1 ip4:198.51.100.25/28 -all"

To complete the setup for receiving inbound email and ensuring valid domain authentication, which TWO DNS resource records must be properly configured in the forward lookup zone?

  1. An MX record mapping the domain apex to the mail server's FQDN alongside an assigned preference number.Answer
  2. A TXT record at the domain apex containing the Sender Policy Framework (SPF) string identifying authorized sending IP addresses.Answer
  3. C
    A PTR record in the forward lookup zone mapping the mail server hostname to its public IPv4 address.
  4. D
    An SRV record configured on TCP port 25 specifying the target hostname and priority for incoming SMTP traffic.
  5. E
    A TXT record requiring DNS query traffic to use TCP port 53 exclusively for all SPF verification requests.

Answer

The correct records to configure are an MX record directing mail traffic to the server's FQDN with a preference value, and a TXT record containing the SPF policy string.
To establish email services, an enterprise requires an MX record to specify the receiving mail server's FQDN along with a preference value. Additionally, domain authentication relies on a TXT record at the zone apex containing SPF specifications (v=spf1...v=spf1...) to declare authorized sending IP addresses.

Step-by-Step Solution

1
Identify the record type required for inbound email routing.
Inbound SMTP servers are discovered by querying Mail Exchanger (MX) records, which point to an A/AAAA record target and include a preference priority.
External sending mail servers query MX records for the destination domain to determine where to deliver message payloads.
2
Identify the record type required for email authentication and SPF policy publication.
Sender Policy Framework (SPF) policies are published using TXT resource records placed at the domain apex.
Receiving mail servers retrieve TXT records containing the 'v=spf1' prefix to evaluate whether the sending server's IP is permitted to send mail for that domain.
3
Evaluate why alternative options are invalid for forward zone email configuration.
PTR records belong in reverse lookup zones, SRV records are not used for standard SMTP host discovery, and DNS TXT queries operate normally over UDP port 53.
Correct DNS design requires matching record functionality and zone types to protocol standards.

Key Concept

DNS Infrastructure and Resource Record Functions (MX and TXT/SPF)
Estimated Time:2m 0s
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Topics

DNS Infrastructure and Record Types

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