You issue the show ntp associations detail command on Router2 and receive the following output:
Router2#show ntp associations detail
10.0.12.1 configured, authenticated, our_master, sane, valid, stratum 3
ref ID 127.127.1.1, time BF6C06E0.55040FD5 (09:02:04.717 UTC Thu Jul 25 2013) <output omitted>
Which of the following is true? (Select the best answer.)

A.
Router2 has successfully authenticated the NTP clients connected to Router2.

B.
NTP on Router2 is synchronized with a master on another device.

C.
NTP on Router2 is synchronized with itself.

D.
Router2 has been configured with an NTP stratum level of 3.

Explanation:
Network Time Protocol (NTP) on Router2 is synchronized with an NTP master on another device. Specifically,
NTP on Router2 is synchronized with the NTP peer that has the IP address of 10.0.12.1. The show ntp
associations command displays both the address of the NTP server from which the client obtains its time and
the address of the reference clock to which the NTP server is synchronized. When issued with the detail
keyword, you can additionally determine the IP address of the NTP peer from which time was synchronized, the
NTP source authentication status, the NTP hierarchical status of the server from which time was obtained,
whether the NTP peer passes basic sanity checks, whether NTP believes the time is valid, and the stratum of
the NTP peer.
NTP on Router2 is not synchronized with itself. If Router2 were the NTP master in this scenario, the output of
the show ntp associations detail command would display the peer’s IP address as 127.127.1.1. The IP address
of 127.127.1.1 typically indicates the local NTP server. Furthermore, the presence of our_master in the output
indicates the status of the device at the NTP peer IP address of 10.0.12.1, not the status of the local device.
Finally, the ref ID field in the output in this scenario indicates a reference clock of 127.127.1.1. The ref ID field
contains the IP address of the NTP peer’s source of time, not the local device. Therefore, the device with the IP
address of 10.0.12.1 has obtained its time from its own local NTP server.
There is no information in this scenario that indicates whether Router2 has successfully authenticated the NTP
clients connected to Router2. The presence of the term authenticated in the output of the show ntp associations
detail command in this scenario indicates that the time source has been authenticated, not the client.
Router2 has not been configured with an NTP stratum level of 3. The stratum field in the output specifies the
NTP stratum level of the NTP peer, not the local device. NTP uses stratum to establish a hierarchy of
authoritative time sources. The stratum value is typically a representation of the difference in accuracy, or
network delay, between the NTP client and Universal Coordinated Time (UTC). An NTP client that receives its
time from an NTP server is usually operating with a higher stratum value, and thus lower accuracy, than the
NTP server from which the client obtained the time.

Cisco: Cisco IOS Basic System Management Command Reference: show ntp associations