Which of the following is NOT a potential reason for th…

You have a router that is not syncing with its configured time source. Which of the following is NOT a potential reason for this problem?

A.
The reported stratum of the time source is 12

B.
The IP address configured for the time source is incorrect

C.
NTP authentication is failing

D.
There is an access list that blocks port 123

Explanation:
A reported stratum of 12 will not cause a router’s inability to synchronize with its configured time source. The stratum value describes the device’s distance from the
clock source, measured in NTPserver hops. When a router reports a stratum value over 15, it is considered unsynchronized. Therefore, a report of 12 could be
normal.
The other options describe potential reasons for a lack of synchronization.

When you are configuring the local router with a time source, if the IP address configured for the time source is incorrect, then no synchronization will occur.
If NTP authentication is configured between the local router and its time source, and that process is failing (for example, due to a non-matching key or hashing
algorithm), then synchronization will not occur.
If there were an access list applied to any interface in the path between the local router and its time source that blocks port 123 (the port used for NTP), then
synchronization will not occur.
Objective:
Infrastructure Services
Sub-Objective:
Configure and verify NTP operating in client/server mode

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus6000/sw/system_management/7x/b_6k_System_Mgmt_Config_7x/configuring_ntp.html