Re: about sFlow instance

From: neil mckee <>
Date: 08/25/05
Message-Id: <>

Hello Kobayashi-san,

The purpose of these data-source instances is to allow two collectors
to monitor the same switch or router. It is unlikely that two
instances would ever be configured to send sFlow to the same
collector on the same UDP port. There would be no advantage in doing
that. That is why there is no instance field in the datagram. Were
you asking because you want to detect this as an error condition?

You are correct that the instances should operate in parallel and be
independent of one another. Ideally there would be a separate
hardware sampling engine for each instance (with a separate random
number generator). However, the reality is that most hardware
implementations have only one sampling engine available for each
interface. The discussion about cascading and sub-sampling was to
show how you can still make the instances operate independently and
in parallel, even when they are sharing the same hardware sampling
engine below (the hardware is configured to sample with a rate equal
to the highest-common-factor, and in software each instance uses sub-
sampling to get back to their desired sampling rate).

Does this answer your question?

Neil McKee

On Aug 24, 2005, at 8:29 PM, kobayashi atsushi wrote:

> Hi,
> I have some question about sFlow instance in sFlow version 5.
> I understood that the Data Source can have one or more sFlow instances
> that have their own Sampling Rate in sFlow version 5.
> But,the sFlow version 5 datagram doesn't contain the field of sFlow
> instance.I wonder that the sFlow Agent can't send the sampling rate of
> sFlow instance.
> For example,there are two sFlow instances in some Data source.Their
> Sampling Rate was different and these sFlow instances operate by
> parallel.
> I think that the Flow sample that is sampled by one instance should be
> distinguished in sFlow datagram.
> In page 10 of the sFlow version 5 document,it is described as a
> example
> that two sFlow instance operate by cascade(sub-sampling).
> I wonder that sFlow instances can't operate by parallel.
> I want to know in detail about sFlow instance.
> Any help will be appreciated.
> Regards,
> ---
> NTT Information Sharing Platform Lab.
Received on Thu Aug 25 12:58:00 2005

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