Is it possible to confuse ntpd's freq error measurement procedure?



Hello.

I have two ntpd peers which exchange time between themselves and also
receive time from external server.
I believe that at some moment connection to external server was lost and
time on these two peers drifted a bit.

When connection to external server was restored both ntpd on both peers
logged something like:
Jun 5 13:21:09 peer0 ntpd[5052]: frequency error 18158 PPM exceeds
tolerance 500 PPM

After that there were a lot of messages with not so big freq error:
Jun 5 13:23:18 DIG ntpd[5052]: frequency error 608 PPM exceeds tolerance
500 PPM

When an operator saw time difference with external server about 30sec he
just restarted ntpd on both nodes and surprisingly freq error messages
disappeared. Now difference is about 1ms and stability stays about 0.021

So my question is: is it possible to confuse ntpd's freq error measurement
with some wrong settings?


My config is:
-----------------------------------------
driftfile /var/lib/ntp/drift
keys /etc/ntp/keys

restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict -6 ::1

server 127.127.1.0 noselect
fudge 127.127.1.0 stratum 10

restrict 192.168.0.240 mask 255.255.255.240

tinker step 0
tos minclock 1 minsane 1

peer 192.168.0.241 burst iburst minpoll 4 maxpoll 6 prefer true
server **external-server-ip** burst iburst minpoll 4 maxpoll 6 true
-------------------------------
.