[j-nsp] Inline IPFIX sampling rate

Scott Granados scott at granados-llc.net
Tue Jul 25 09:44:05 EDT 2017

I would be interested in this as well.  My understanding was that the sampling rate in hardware was always set to 1:1 and the sample rate value was sent as the scaling factor for the sampling / reporting tool.  Changing the rate had no practical effect to the actual data.  If this has changed I’d be curious to know as well.

> On Jul 25, 2017, at 5:30 AM, Pavel Lunin <plunin at gmail.com> wrote:
> Hi list,
> It's been long time I didn't write here :)
> Does anyone know in details how sampling-rate works (if it does) for inline
> IPFIX on MX/Trio?
> AFAIR sampling rate config hadn't had any meaning for inline IPFIX until
> some version of JUNOS. It used to be always 1, no matter what you have in
> the config.
> Question 1: If correct, which version it was when it's changed?
> As of the 2nd edition of the MX book, "input rate" must follow the formula
> “input_rate=2^n-1”. But it's somewhat poorly explained what it means.
> Question 2: Do I correctly understand that the value, configured with
> ”sampling instance <blah> rate <x>”, must conform to this rule. Here <x> is
> not the index of power of two (aka n in the formula above), it is the
> actual sampling rate (result of the formula), right?
> Question 3. Given that I correctly understand the previous point, what if I
> configured something that does not conform to this rule e. g. "rate 100"? I
> suspect that it should lead to "rate 1" being programmed in the PFE but
> can't find a way to check this out. Anyone knows a uKernel command to
> verify what is actually applied at the PFE level? It seems that "show
> sample instance summary" just replicates the config values.
> Regards,
> Pavel
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