[Nagios-devel] Nagios check_ping High RTA

Andreas Ericsson ae at op5.se
Thu May 21 11:02:35 UTC 2009


Muthurasu.Palsamy at slashsupport.com wrote:
> Hi
>  
> a) Whenever i do normal ping(from shell)of a host takes less than 1ms, but when 
> i do ping using check_ping plugin it gives me 20ms and some times its shows less 
> than 1ms.
> So there is an fluctuation happening in nagios check_ping plugin.
>  

Normal ping measures round trip time, whereas check_ping measures round trip time
*average*. Normally when a host that hasn't been connected to for some time is
about to receive a packet, routers and switches have to resolve the hosts ARP
address, which takes 5-20ms in a local network. Since check_ping only sends 5
ICMP ECHO requests by default, the (much) higher initial round trip time plays
a large relative role for it.

> b) Is there any way to avoid those fluctuation?  
> 

Increase the ARP cache size on your switches.

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

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