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

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

• A. When a primary SOA is higher than a secondary SOA
• B. Never; zone transfers are manual
• C. Only during startup
• D. When a secondary SOA is higher than a primary SOA

Answer: (A)

The key idea here is how DNS zone transfers are triggered by the serial numbers in the SOA record. In a master/slave DNS setup, the primary (master) holds the authoritative zone data and marks changes by increasing the serial number in its SOA record. The secondary (slave) keeps its own copy and periodically checks whether its serial is up to date. If the primary’s serial is higher than the secondary’s, the secondary knows its copy is out of date and requests a zone transfer (to fetch the latest records). This automatic synchronization keeps all servers consistent without manual intervention. That’s why the correct condition is when the primary SOA is higher than the secondary SOA. The other options don’t fit: zone transfers aren’t manual by default, they aren’t limited to startup, and transfers don’t occur because the secondary’s serial is higher.

The key idea here is how DNS zone transfers are triggered by the serial numbers in the SOA record. In a master/slave DNS setup, the primary (master) holds the authoritative zone data and marks changes by increasing the serial number in its SOA record. The secondary (slave) keeps its own copy and periodically checks whether its serial is up to date. If the primary’s serial is higher than the secondary’s, the secondary knows its copy is out of date and requests a zone transfer (to fetch the latest records). This automatic synchronization keeps all servers consistent without manual intervention.

That’s why the correct condition is when the primary SOA is higher than the secondary SOA. The other options don’t fit: zone transfers aren’t manual by default, they aren’t limited to startup, and transfers don’t occur because the secondary’s serial is higher.