Ntp string disappear after specifying "prefer" on it - Nexus 9K

[Simone C]

Hello all,

I noticed a weird behaviour during the ntp configuration of a server into a Nexus 9K device.
basically if I launch the command "ntp server test use-vrf management" it's all good and the string is visible in the running config:

SWITCH(config)# ntp server test use-vrf management
SWITCH(config)# exi
SWITCH#
SWITCH# sho run | i ntp
ntp server test use-vrf management

But if i go back and add the "prefer" condition on this string, then it disappear:

SWITCH(config)# ntp server test use-vrf management
SWITCH(config)# exi
SWITCH#
SWITCH# sho run | i ntp
ntp server test use-vrf management
SWITCH#
SWITCH#
SWITCH# conf t
SWITCH(config)# ntp server test prefer use-vrf management
SWITCH(config)# exi
SWITCH#
SWITCH#
SWITCH# sho run | i ntp
SWITCH#
If i delete the entry of this string and write it again with the "prefer" status from the beginning, then it works properly and it shows up into the running config.

I did not find any bug related to this behaviour, so I cannot actually tell if it is just a cosmetic one or not. Current Nexus Software release is 10.2(6) and model is N9K-C93180YC-FX3.

Thanks for any advice or tip!

[MHM Cisco World]

did you config multi NTP server ? I think this command use only when there are multi NTP server 
try add dummy one and use prefer 

MHM

[Simone C]

Yes sorry I did not specify that i configured two other NTP servers beside the test one (both dummies to try that) and the behaviour is the same. If i configure all the three NTPs without specify a preferred one everything goes fine and all the three strings are showing in the configuration. But if i decide to change and set one of them as the prefer, and launching the command "ntp server DUMMY prefer use-vrf management" when the string "ntp server DUMMY use-vrf management" is present, then it deletes the string. I always need to first negate the previous command and then launch the one with the "prefer" specification.