[ovs-dev] [ovs-dev, PATCHv3] ofproto-dpif-sflow: Add snaplen for sample action and sFlow.

[William Tu]

Hi Wenyu and Daniel,

Thanks for your feedback.

On Mon, Jul 11, 2016 at 1:50 AM, Wenyu Zhang <wenyuz at vmware.com> wrote:
> Hi William,
>
> In your patch, no codes about supporting “snaplen" in IPFIX included. IPFIX
> still get the length of  packet as before, whatever the packet is truncated.
> If user put a non-zero ‘snaplen’ in IPFIX sample action, the IPFIX result
> should be incorrect. So the ‘snaplen’ in the flow-based IPFIX action may
> cause some issue without the complete supporting.

You're right. If IPFIX wants to use the snaplen feature, then the
IPFIX implementation needs to be aware of receiving a truncated packet
instead of the original packet. Much similar to the change I made in
ofprot-dpif-sflow.c.

>
> Considering that ‘snaplen’ may help reduce the cost to copy packets, it
> should help IPFIX too. We may work out a separated patch to support
> “snaplen” in IPFIX, including both bridge based IPFIX and flow based IPFIX.
>

Skimming through the IPFIX RFC, I don't have any concrete idea which
IPFIX configuration could translate to the snaplen, or how IPFIX could
use snaplen. For sFlow, it's straightforward because it has
"sFlowMaximumHeaderSize" which could directly translate to snaplen. Do
you have any suggestion?

Regards,
William