Hi,
NTP uses the concept of a stratum to describe how many NTP hops away a machine is from an authoritative time source.
The stratum is a number between one and 15 that indicates how far removed the server is from a precision reference (atomic) clock.
Generally systems that are directly synchronized to an atomic clock report their stratum as one.
A host that is synced to a stratum one NTP server but also serves as an NTP server for other hosts reports its stratum as two to those hosts,
with each successive layer of servers having a stratum that is one higher than its parent.
The "Strata too high - too many indirections from sensor to master NTP server" error message appears when the sensor attempts
to sync to a server that reports its stratum as 15. This is because a server stratum value of 15 makes the sensor stratum value 16,
which is illegal. As a result, the sensor instead rejects the server and displays the error message you are seeing.
If your Core switch is configured as NTP master, you can change it's stratum level using the below command:
Rack1R1(config)#ntp master ?
<1-15> Stratum number
Hope this helps,
Stijn