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Zorluk: ZorDNS Infrastructure and Record Types

A network engineer is deploying a new dual-stack email gateway (mail.corp.example.commail.corp.example.com) for the domain corp.example.comcorp.example.com. External mail servers are failing to deliver messages to the organization, and secondary DNS servers fail to synchronize large zone files from the primary authoritative DNS server. The engineer runs diagnostic queries and receives the following output:

text
$ dig +noall +answer mail.corp.example.com AAAA
mail.corp.example.com. 3600 IN AAAA 2001:db8:85a3::8a2e:370:7334

$ dig +noall +answer corp.example.com MX
(no output returned)

Which TWO of the following DNS infrastructure and record configuration actions must be taken to resolve mail delivery and DNS synchronization issues?

  1. Add an MX record for corp.example.com pointing to mail.corp.example.com with an appropriate preference value.Cevap
  2. Ensure firewall rules permit TCP traffic on port 53 between primary and secondary DNS servers for zone transfers.Cevap
  3. C
    Create a CNAME record at the zone apex (corp.example.com) pointing directly to 2001:db8:85a3::8a2e:370:7334.
  4. D
    Replace the AAAA record with a PTR record in the primary forward lookup zone file.
  5. E
    Reconfigure DNS zone transfer traffic to use UDP port 25 to match mail delivery protocols.

Cevap

To resolve mail routing and DNS zone synchronization failures, an MX record must be added pointing to mail.corp.example.com, and firewall security rules must allow TCP traffic on port 53 for zone transfers.
Mail delivery requires an explicit MX (Mail Exchanger) resource record mapping the domain to the mail gateway hostname (mail.corp.example.com). Furthermore, DNS zone transfers between primary and secondary DNS servers rely on reliable TCP transport over port 53 because zone data transfers involve multi-packet payloads.

Adım Adım Çözüm

1
Analyze the MX lookup diagnostic output.
The dig query for MX records returned no answer, indicating external sending servers cannot identify the designated mail exchanger for corp.example.com.
Creating an MX record pointing to the mail gateway hostname with a preference integer enables external MTA routing.
2
Analyze the zone transfer failure requirement.
Standard DNS queries use UDP port 53, but zone transfers (AXFR/IXFR) and oversized DNS payloads require connection-oriented TCP port 53 transport.
Firewalls blocking TCP port 53 prevent secondary name servers from synchronizing zone updates from primary authoritative servers.

Anahtar Kavram

DNS Record Types and Transport Protocols
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DNS Infrastructure and Record Types

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