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Re: [bmwg] [answer to Bill Cerveny] RE: New Version Notification for draft-janovak-bmwg-ipflow-meth-00 [answer to Bill Cerveny]
Hi,
> I just think that making statements about a router's flow
> handling and
> reporting capabilities aren't complete if it can't be verified that
> the flow data reported is accurate.
The draft covers it to certain extent - checking the flow monitoring
counters to make sure that the expected flow conditions are met
- e.g. the network device reacts to and registers all the flows.
Something in terms of what you suggest is certainly possible, but the
biggest concern we always met was "what is flow monitoring performance
and where (which device in the network) can I afford to enable it".
The accuracy of the data comes always as second (when you know you
can actually do it :-) at all). It would be possible to check the
individual flows
counters on the network device in most of the cases described in the
draft (but not with cache overflow) but not as part of the performance
measurement since such a check would heavily load the CPU when
collecting
the necessary outputs. May be we can discuss this in Dublin ??
I am not in the position to suggest anything regarding external
collectors
since I am not familiar with them and never tested them and would like
to
keep this draft scope to just the network devices.
Jan
The climate of Edinburgh is such that the weak
succumb young .... and the strong envy them.
Dr. Johnson
> -----Original Message-----
> From: Bill Cerveny [mailto:bill at wjcerveny.com]
> Sent: 17 July 2008 03:53
> To: Jan Novak (janovak)
> Cc: bmwg at ietf.org
> Subject: Re: [bmwg] [answer to Bill Cerveny] RE: New Version
> Notification for draft-janovak-bmwg-ipflow-meth-00 [answer to
> Bill Cerveny]
>
> Comments below ...
>
> Bill
>
> On Jun 11, 2008, at 9:43 AM, Jan Novak (janovak) wrote:
>
> > Hi Bill,
> >
> > I am sorry, was on holidays and missed your answer ....
> >
> >> devices, the throughput measurement wouldn't be
> appropriate. Perhaps
> >> the scope of this document should be specifically on
> network devices
> >> that transit network traffic?
> >
> > Yes, the intention was to make it specific for only network devices.
> > Will review the text to make sure it is clear.
>
> OK
>
> >
> >
> >> Wouldn't a big consideration be the quality and accuracy
> of the flow
> >> data? How would the accuracy of the generated flow be
> evaluated?
> >> The
> >
> >> flow generating capabilities of a network device is certainly less
> >> useful if the device's flow accuracy degrades when it is transiting
> >> more traffic.
> >
> > I would consider this out of the scope since to check that
> the testing
> > would
> > have to involve some external collector and the way those
> handle data
> > is even more complex than what happens on the network devices when
> > just registering the traffic.
> > I will think about it yet, but based on the testing we have done I
> > don't
> > quite see how to do it.
>
> Couldn't you do something like send a known set of network traffic
> (defined by number of packets, types of packets, packet sizes, etc)
> across the router? If the collector's interpretation of of the flow
> data matches what was sent across the router, a statement could be
> made about flow accuracy. If the collector's interpretation of the
> flow data does not match what was sent across the router, then a
> statement of accuracy cannot be made. If the collector is unable to
> keep up with the flow data, perhaps another way of verifying the
> accuracy of the flow may be recording the flow data and playing it
> back at a rate that a collector could understand.
>
> I just think that making statements about a router's flow
> handling and
> reporting capabilities aren't complete if it can't be verified that
> the flow data reported is accurate.
>
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