How are packet loss and RTA Calculated?

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How are packet loss and RTA Calculated?

Postby silverbenz » Tue Dec 04, 2012 1:34 am

Hi all,

Trying to figure out how the host check packet loss/rta figures are calculated. I'd also like to know how the ping service check packet loss figure is calculated. I'm trying to tune our Nagios instance and, it appears to me at least, that the default host-based (check-host-alive) packet loss figure of Warning=80% seems surprisingly high. I know this is configurable, but there must be a reason why this is the default.

With regard to the ping service check (check_ping), the values are closer to what might seem reasonable (warning = 20% loss, etc). However, I'm getting Warning alerts in my config saying that I have a packet loss value of either 16%, 28%, 37% or 44%. All of these are actual examples. As far as I can tell the ping check sends 5 "pings". I can't reconcile how the packet loss percentages are arrived at, given that 1 packet lost should equal 20%, right?

Happy to be directed to documentation if that answers my questions, but I haven't been able to find any so far. All help appreciated.

Many thanks,
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Re: How are packet loss and RTA Calculated?

Postby slansing » Tue Dec 04, 2012 2:46 pm

Correct, I believe by default the ping check runs a ping echo 5 times, packet loss is derived from the amount of ping's which get through and echo back. So in reality if one ping was dropped that would equal roughly 20% packet loss as you stated. As far as RTA "round trip average" goes, that is the amount of time it took "ON AVERAGE" for those 5 pings to reach their destination and echo a return. So, packet loss calculates the amount of connection loss, and RTA calculates the time it took you to send and receive a ping echo.
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