check_ntp -- need a little bit help

[Schimpke, Dr. Thomas / bhn]

Hi all,

I've a couple of ntp servers/clients running. I wanted to check them with
check_ntp, but got (almost always) the message "UNKNOWN: Dispersion too
high". The dispersion is hard coded in the plugin to 15 (ms), the actual
dispersion was much below. I was a little bit curios about this issue, so I
looked at the source code and found, that check_ntp basically parses the
output of the command xntpdc/ntpdc -s. Running "xntpdc -s hostname" resulted
in an error message: "*** Server reports a format error in the received
packet (shouldn't happen)". 

According to Dave Mills (see google...) there is *no gurantee* that xntpdc
is interoperable between two releases of the ntp package. He recommands
useing ntpq instead (xntpdc seems to exist mainly for debugging purposes). 

I've patched the plugin to use ntpq (basically I run ntpq -p, the dispersion
is reported in the 10th field). This seems to work fine (if someone is
intrested in a patch, drop me a note). The problem is, which peer to take
from the output (you normally have several peers on a server/client running
the ntp process). This  is not a ntpq issue -- you have the same problem, if
you use xntpdc: you get a list of peers. If you do nothing about it, you get
the dispersion of the last peer reported in the list (not good), in my case
it's the LOCAL peer, which is unintresting. Instead the list should be
processed according to the tally codes (the value in the first column of the
list). But even then: do I take the sys.peer/pps.peer or the mean value of
all peers used in the combine algorithm...

I'm not even sure, if the dispersion is a good measure of the ntp "state"
for ntp configured as a client on a local network. The "offset" of the clock
sems to be more appropriate, but I'm not a ntp specialist.

Any comments ?

Greetings,

Thomas
 


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