Re: [IPFIX] timestamps, exporters, and other animals

On Tue, Oct 11, 2011 at 05:49:13PM -0700, Josh Bailey wrote:
 
> I think it'd be good thing to specify an association between a
> timestamp, and an exported OID, flow, etc. When exporting an OID,
> for example, I would like a way to know within some limit of
> certainty when that OID value was actually sampled.
> 
> A problem I find with SNMP is that the client can only use its own
> timestamp of the server's reply to guess when the requested variable
> was sampled. If there is uncertainty in the server implementation
> that adds some delay between sampling and sending the response
> (without even addressing variable network delay), there's no way to
> know when the object was sampled with any certainty.

In SNMP land, you typically fetch sysUpTime together with the counters
(also to detect discontinuities). This means you get a timestamp that
is attached to the counter by the 'server' and this timestamp can take
care of the network delay part. That said, implementations sometimes
for efficiency reasons do not read out hardware registers on every
request if you poll very fast - so there might be some notable delay
in how counter changes are reported (but then typical SNMP poll cycles
are counted in minutes).

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1, 28759 Bremen, Germany
Fax:   +49 421 200 3103         <http://www.jacobs-university.de/>
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