[j-nsp] Inline IPFIX sampling rate

Pavel Lunin plunin at gmail.com
Tue Jul 25 05:30:37 EDT 2017

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.


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