check_ping oddities

[Mascardo, Erwin]

>-----Original Message-----
>From: nagios-users-admin at lists.sourceforge.net 
>[mailto:nagios-users-admin at lists.sourceforge.net] On Behalf Of 
>Dale Blount
>Sent: Thursday, 29 September, 2005 13:53
>To: nagios-users at lists.sourceforge.net
>Subject: [Nagios-users] check_ping oddities
>
>
>Hi,
>
>My check_ping is defined like this:
>
>define command{
>        command_name                    check_ping
>        command_line                    $USER1$/check_ping -H
>$HOSTADDRESS$ -w $ARG1$ -c $ARG2$ -p 6 -t 20
>}
>
>Yet I get output at times like:
>
>PING WARNING - Packet loss = 71%, RTA = 89.44 ms
>(warn is 60%, crit is 80%, so WARNING is correct).
>
>and
>
>PING WARNING - Packet loss = 25%, RTA = 17.44 ms
>(warn is 20% and crit is 40%, so WARNING is correct).
>
>
>And now to the question.  How can 71% or 25% be a result when 6 packets
>are sent?
>
>Thanks,
>
>Dale

I've seen this happen on some of our WAN hosts. Near as I can tell,
check_ping (we use check_icmp, but I saw it happen in the check_ping
days as well) bases its success rate on the number of replies -- if you
use 5 packets as your standard, then it waits to hear the response from
packet #4 before reporting its result. And it sends out packets until it
gets that specified reply. (I know, I could read the source to get a
definitive answer...just feeling too lazy at the moment.)

In my situation, over an 800 ms WAN link, there was usually time to send
6 packets while waiting for the result on the 5th, so I'd get packet
losses of 16% when things were otherwise okay. What's puzzling me in
your situation is your latency -- what happened to me shouldn't be
happening to you with those kind of ping times.

--Erwin

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