You updated your primary server with new hosts. However, you notice that the
secondary server has not updated its contents. Which value must you increment on your
primary server so that the secondary server will update its contents?

A.
Expire

B.
Retry

C.
Refresh

D.
Serial

Explanation:
We need a zone transfer not updates of individual records. By upping
the serial number, the secondary will see that its copy is old, and will request a new
copy of the zone. This causes a zone transfer and all the records would be sent to the
secondary server.
Incorrect Answers:
A: The Expire value determines the life time of the DNS records. Changing this valuewould not
cause a zone transfer.
B: The retry is how often the cache needs to check back if it can’t contact the server for arefresh.
Changing this setting would not cause a zone transfer.
C: The refresh time is how often the cache needs to check for any changes. Configuringthis value
would not cause a transfer.