To securely use dynamic DNS updates, the use of TSIG is recommended. Which TWO statements
about TSIG are true?

A.
TSIG is used for zone data encryption

B.
TSIG is a signal to start a zone update

C.
TSIG is used in zone files

D.
TSIG is used only in server configuration

E.
Servers using TSIG must be in sync (time zone!)

Explanation:
See http://tools.ietf.org/html/rfc2845
To defend against attackers resending old messages the time of the message is used in the hashing
of the message, which means that servers must be synced.