312-50V13 Question #87: Real Exam Question with Answer & Explanation

Question

Under what conditions does a secondary name server request a zone transfer from a primary name server?

Options

• AWhen a primary SOA is higher that a secondary SOA
• BWhen a secondary SOA is higher that a primary SOA
• CWhen a primary name server has had its service restarted
• DWhen a secondary name server has had its service restarted
• EWhen the TTL falls to zero

Explanation

A secondary name server requests a zone transfer from a primary name server when it detects that the primary's Start of Authority (SOA) record indicates a newer version of the zone data.

Common mistakes.

• B. If a secondary's SOA serial number is higher than the primary's, it implies the secondary might have newer data, which is an anomalous situation in a typical primary-secondary setup and would not trigger a transfer from the primary.
• C. While a primary name server restart might be followed by zone changes, the direct condition that triggers a secondary to request a transfer is the serial number difference in the SOA record, not the restart itself.
• D. When a secondary name server restarts, it will check the primary's SOA record to determine if a zone transfer is needed, but the actual condition for the request is the primary having a higher SOA serial number, not just the restart.
• E. The TTL (Time To Live) value applies to individual resource records and dictates how long clients should cache a record, it does not directly trigger zone transfers between DNS servers.

Concept tested. DNS zone transfer triggers (SOA serial)

Reference. https://learn.microsoft.com/en-us/windows-server/networking/dns/deploy/zone-transfers

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