[c-nsp] A9K Netflow export drops

Wed May 25 11:05:32 EDT 2016

Chris - Thanks, I've not yet opened one, but would be curious to hear the outcome of yours as it may save doubling up.

Jimmy - If I take the sampling to 1:1 then yes I can achieve this event, however, we appear to be at the limit of the 'exporter' not the 'monitor/cache' so at present the cache is not being exceeded.

Cheers guys!

Robert Williams
Custodian Data Centre
Email: Robert at CustodianDC.com
http://www.CustodianDC.com

-----Original Message-----
From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jimmy
Sent: 23 May 2016 17:16
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] A9K Netflow export drops

Hi,
Just wondering,
Did you find something like this on your syslog ?
 %MGBL-NETFLOW-6-INFO_CACHE_SIZE_EXCEEDED : Cache size of 1000000 for monitor xxx has been exceeded

Regards,
Jimmy Hng.

On Tue, May 24, 2016 at 12:02 AM, Robert Williams <Robert at custodiandc.com>
wrote:

> Hi,
>
> Doing some more digging, found this from 2014:
>
> Netflow specific scale and Limitations are described below:
>   1. Supports configurable Sampling Rate 1:1 ~ 1: 65535
>   2. Supports only up to 4 Sampling Rates (or Intervals) per Ethernet
> LC LC; no such limit for Enhanced Ethernet LC.
>   3. Up to 4k interfaces/sub-interfaces (4K system limitation) can be
> configured with flow monitor per system.
>   4. Supports up to 8 flow exporters per flow monitor
>   5. Supports up to 1 million flow entries per LC
>   6. Supports up to 50k flows per second with LC CPU usage up to 50%
> per Ethernet LC LC
>   7. Supports upto 100K flows per second with LC CPU usage up to 50%
> per Enhanced Ethernet LC LC
>   8. Netflow scale is increased to 200Kpps on Enhanced Ethernet LC
> based LCs
>   9. Supports exporting packet rates up to 50k flows per second (100K
> flows per sec on Enhanced Ethernet LC based LCs) with LC CPU usage up
> to 50%
>
> "Irrespective of the rate at which the NP punts the records to CPU,
> exporter picks up a maximum of 2000 records at a time from the cache
> that are eligible for export (timers, network/TCP session events,
> etc). This is basically to avoid NetIO dropping the packets due to
> lack of b/w. When the exporter wakes up again, it repeats the same."
>
> So, it can collect 100k flows per second, but can only export 2k each
> time it runs the exporter. The interval for the exporter is unclear however.
>
> I've also found out why this is such an issue on our 9001 but not on
> any of our 900x larger chassis. Looks like on those the hardware punt
> is being limited to 25kpps per NP because we have some BVIs with Netflow on them.
> This causes it to distribute the rate limit for punting to ALL the NPs
> on the LC, even when only two ports are involved in Netflow. Thus,
> it's "sampled sampling" and so the rate of flow data is significantly
> lower than the 9001 which is allowing all 100kpps on one NP which has
> 4 x 10G interfaces punting into it.
>
> mmm...
>
>
>
> Robert Williams
> Custodian Data Centre
> Email: Robert at CustodianDC.com
> http://www.CustodianDC.com
>
> -----Original Message-----
> From: Dale W. Carder [mailto:dwcarder at wisc.edu]
> Sent: 23 May 2016 16:02
> To: Robert Williams <Robert at CustodianDC.com>
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] A9K Netflow export drops
>
> Thus spake Robert Williams (Robert at CustodianDC.com) on Sat, May 21,
> 2016 at 10:59:50AM +0000:
> >
> > I've got an issue on one of our smaller 9001 boxes which is puzzling me.
> > It suffers from a high rate of netflow export drops (not cache
> > drops)
> shown here:
> >
> > So from what I understand, it is capturing the flows OK but is
> > unable to
> get the flow data out, for some reason.
>
> I can confirm that our 9k's suffer from this also.
>
> The last I checked you can export at the rate of 2000 flows/sec.  I
> have not looked in 2 years or so to see if this limit was configurable
> yet.
>
> > So - what am I missing here? Surely with a cache capability of 1M it
> should be ok to export flows when were are only around 30,000 of them
> nicely ticking over?
>
> join the club.  :-(
>
> Dale
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