What are these?
HW: Cisco Catalyst 3560X (12.2(58r)SE1)
Log file:
1612160: Nov 26 07:39:05.935: NTP Core (NOTICE): frequency error nan PPM exceeds tolerance 0. PPM
1612161: Nov 26 07:39:21.924: NTP Core (NOTICE): frequency error nan PPM exceeds tolerance 0. PPM
1612162: Nov 26 07:39:39.918: NTP Core (NOTICE): frequency error -0. PPM exceeds tolerance 0. PPM
1612163: Nov 26 07:39:55.907: NTP Core (NOTICE): frequency error -0. PPM exceeds tolerance 0. PPM
Config:
ntp master
ntp server 10.255.0.1 prefer
ntp server 91.240.0.5