[ovs-discuss] Limitations of Mininet

[Nicholas Bastin]

On Mon, Jul 6, 2015 at 3:46 AM, Adil Ahmad <adilahmad17 at gmail.com> wrote:

> I was trying to get flow statistics and the implementation that I'm
> working on requires that I get flow stats in RTT timescales. But, the flow
> statistics show that the packet count counter is updated after almost a
> second for OF 1.0 swtiches using POX. I want the packet counters to be
> updated at every iteration around 1 ms. Is that a limitation with mininet
> or OF 1.0?
>

This is a limitation of mininet, although what mininet does (and OVS, by
extension) is much closer to what you want than any other OF device will do.

There is exactly zero chance that a real OF network (or any network) can
update packet counters on a per-ms basis.  Most hardware does so on a 1-10s
interval, and the shorter the interval the more sampling is used (and thus
the more inaccurate it may be).

This is not specific to OF - SNMP, NetFlow, sFlow, etc. also suffer from
this kind of update and sampling issue.  As a practical matter if you want
1ms accurate counters you will need to employ high-speed taps in your
network.

--
Nick
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